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Prior H1N1 Influenza Infection and Susceptibility of Cleveland Family Study Participants during the H2N2 Pandemic of 1957: An Experiment of Nature
Abstract
During a pandemic, influenza vaccines that rely on neutralizing antibodies to protect against matched viruses might not be
available early enough. Much broader (heterosubtypic) immune protection is seen in animals. Do humans also have cross-subtype
immunity? To investigate this issue, archival records from the Cleveland Family Study, which was conducted before and during
the 1957 pandemic (during which a shift from subtype H1N1 to H2N2 occurred), were analyzed. Only 5.6% of the adults who had
had symptomatic influenza A in earlier study years developed influenza during the pandemic, despite living in households with
participants who had influenza. In contrast, 55.2% of the children who had had symptomatic influenza A contracted it again.
These findings suggest an impact of accumulated heterosubtypic immunity during a pandemic. Such immunity, as well as its implications
for vaccination, should be further investigated
... During a pandemic, a rigorous question arises in the scientists' mind whether humans may possess the crosssubtype immunity in order to develop an appropriate vaccine [28]. Such a puzzle was nearly resolved through the analysis of the archival records of the Cleveland Family Study before and during the 1957 pandemic; i.e., during the shift from subtype H1N1 to H2N2 to investigate the development of the heterosubtypic immunity. ...
... The H1N1 subtype influenza A virus causing the 1918 pandemic outbreak caused the seasonal epidemics until 1957 when a new influenza A virus of the H2N2 subtype emerged [28]. This was referred to as the ''Asian'' influenza virus, causing the second pandemic after the Spanish flue as stated above [29]. ...
... The H2N2 kept continuing the dissemination of the seasonal influenza from 1957 to 1967; and in 1968 the third pandemic appeared with the new H3N2 subtype [29,30]. The H2N2 subtype, causing the pandemic in 1957, indeed continued to disseminate in humans till 1968 [28][29][30][31]. The antigenic diversity of human H2N2 viruses isolated between the intermittent 12 years (from 1957 to 1968) has been well characterized; and two amino acid substitutions, T128D and N139K, located in the head domain of the H2 hemagglutinin (HA) molecule, have been shown to be the functional determinants of the antigenic change during the evolution of H2N2 subtype [29]. ...
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently causing the respiratory illness termed as the coronavirus disease 2019 or the COVID-19 pandemic. Indeed, the significant increase in deaths in the current days due to influenza around the world started in 1889 is a continued public health threat because of its intermittent style of pandemic outbreaks. An array of research on the influenza viruses has been conducted especially pointing on (1) the development of the anti-viral drugs and the design of probable vaccines on trial basis, (2) the biochemical and genetic aspects underlying the viral pathogenicity, (3) the viral epidemiology, and on (4) the protective immunity against the influenza viruses. Current review briefly discussed the epidemic/ pandemic history of influenza and correlated with the current epidemiology, the possible preventive measures that may be taken by the public health professionals as well as to increase the protective awareness among the general people. The viral reassortments during the initiation of pandemics have also been focused based on the previous literatures.
... Influenza viruses undergo continual genetic mutations and punctuated antigenic changes, which allow them to escape prior immunity and cause new epidemics [3][4][5][6]. In addition, currently two influenza A subtypes, A(H1N1) and A(H3N2), and influenza B co-circulate in humans; and infection of a certain type/subtype can result in partial immunity to influenza strains of the same type/subtype as well as strains across subtypes [7][8][9][10][11][12][13][14][15] and types [16][17][18]. The latter cross-reactive immunity-termed cross-immunity-leads to epidemiological interactions among influenza viruses that, along with viral antigenic changes, shape influenza phylodynamics and epidemic dynamics [19][20][21][22][23][24][25][26][27][28][29][30][31]. ...
... Multiple lines of evidence have suggested cross protection offered by infection of influenza viruses of the same type/subtype as well as across types/subtypes [7][8][9][10][11][12][13][14][15][16][17][18]. However, some studies have reported weak or no heterosubtypic and/or heterotypic cross-immunity [47,53]. ...
... For the immunity period L i , given the wide range reported in the literature (from months to~8 years [76,77]), we tested prior ranges from 1 to 9 years, divided into four 2-year segments (i.e., [1,3], [3,5], [5,7], and [7,9] years) for each type/subtype; this resulted in 4 3 = 64 combinations for the three type/subtypes. Cross-immunity has been observed for influenza strains of the same subtype as well as across types/subtypes [7][8][9][10][11][12][13][14][15] and types [16][17][18]; however, the strength has rarely been reported. We thus tested prior ranges from 0% to 80% of the strength of specific immunity, divided into two levels: [0%, 40%] (low) and [40%, 80%] (high); this resulted in 2 6 = 64 combinations for 6 virus-pairs (c ij , i = H1N1, H3N2, or B and j6 ¼i). ...
Influenza epidemics cause substantial morbidity and mortality every year worldwide. Currently, two influenza A subtypes, A(H1N1) and A(H3N2), and type B viruses co-circulate in humans and infection with one type/subtype could provide cross-protection against the others. However, it remains unclear how such ecologic competition via cross-immunity and antigenic mutations that allow immune escape impact influenza epidemic dynamics at the population level. Here we develop a comprehensive model-inference system and apply it to study the evolutionary and epidemiological dynamics of the three influenza types/subtypes in Hong Kong, a city of global public health significance for influenza epidemic and pandemic control. Utilizing long-term influenza surveillance data since 1998, we are able to estimate the strength of cross-immunity between each virus-pairs, the timing and frequency of punctuated changes in population immunity in response to antigenic mutations in influenza viruses, and key epidemiological parameters over the last 20 years including the 2009 pandemic. We find evidence of cross-immunity in all types/subtypes, with strongest cross-immunity from A(H1N1) against A(H3N2). Our results also suggest that A(H3N2) may undergo antigenic mutations in both summers and winters and thus monitoring the virus in both seasons may be important for vaccine development. Overall, our study reveals intricate epidemiological interactions and underscores the importance of simultaneous monitoring of population immunity, incidence rates, and viral genetic and antigenic changes.
... The first evidence of heterosubtypic protection against a pandemic strain was described by Epstein in the Cleveland family study during the 1957 H2N2 pandemic [90]. The results showed that adults who had laboratory-confirmed H1N1 seasonal influenza virus infections between 1950 and 1957 were three times less likely to have symptomatic laboratory-confirmed pandemic H2N2 influenza virus compared to those who were not previously infected with the seasonal H1N1 influenza virus [90]. ...
... The first evidence of heterosubtypic protection against a pandemic strain was described by Epstein in the Cleveland family study during the 1957 H2N2 pandemic [90]. The results showed that adults who had laboratory-confirmed H1N1 seasonal influenza virus infections between 1950 and 1957 were three times less likely to have symptomatic laboratory-confirmed pandemic H2N2 influenza virus compared to those who were not previously infected with the seasonal H1N1 influenza virus [90]. Recently, during the 2009 H1N1 influenza virus pandemic, individuals with pre-existing IAV-specific CD8 + T cells showed a decreased risk of fever, fewer influenza-like symptoms of illness, reduced illness severity scores, and the absence of viral shedding [17]. ...
Influenza A virus is a respiratory pathogen that is responsible for regular epidemics and occasional pandemics that result in substantial damage to life and the economy. The yearly reformulation of trivalent or quadrivalent flu vaccines encompassing surface glycoproteins derived from the current circulating strains of the virus does not provide sufficient cross-protection against mismatched strains. Unlike the current vaccines that elicit a predominant humoral response, vaccines that induce CD8+ T cells have demonstrated a capacity to provide cross-protection against different influenza strains, including novel influenza viruses. Immunopeptidomics, the mass spectrometric identification of human-leukocyte-antigen (HLA)-bound peptides isolated from infected cells, has recently provided key insights into viral peptides that can serve as potential T cell epitopes. The critical elements required for a strong and long-living CD8+ T cell response are related to both HLA restriction and the immunogenicity of the viral peptide. This review examines the importance of HLA and the viral immunopeptidome for the design of a universal influenza T-cell-based vaccine.
... We found pre-existing CD4 and CD8 T cell responses for sH1N1 virus were associated with the protection against antigenically very divergent pH1N1. This was consistent with the epidemiological evidence from the past pandemics that previous seasonal H1 influenza virus infections were associated with a lower infection risk with newly emerged pandemic H2 strains [40,41]. Also, our previous study demonstrated that the bulk memory cytotoxic T lymphocytes established by sH1N1 infections who have not been exposed to the pH1N1 virus can directly lyse pH1N1 virus-infected target cells in healthy adult volunteers [20], supporting this association. ...
... This suggested there could be heterogeneity in infection risk among individuals with undetectable antibodies, for example, a portion of the elderly was not infected although they had no immunity suggested by HAI titers [44]. Therefore, such T cell-mediated immunity is particularly important in a pandemic setting when most individuals have no immunity against the newly emerged strain, either lowering infection risk or severity [16,40]. Usually, only HAI antibody is measured as a correlate of protection. ...
Background
The protective effect of T cell-mediated immunity against influenza virus infections in natural settings remains unclear, especially in seasonal epidemics.
Methods
To explore the potential of such protection, we analyzed the blood samples collected longitudinally in a community-based study and covered the first wave of pandemic H1N1 (pH1N1), two subsequent pH1N1 epidemics, and three seasonal H3N2 influenza A epidemics (H3N2) for which we measured pre-existing influenza virus-specific CD4 and CD8 T cell responses by intracellular IFN-γ staining assay for 965 whole blood samples.
Results
Based on logistic regression, we found that higher pre-existing influenza virus-specific CD4 and CD8 T cell responses were associated with lower infection odds for corresponding subtypes. Every fold increase in H3N2-specific CD4 and CD8 T cells was associated with 28% (95% CI 8%, 44%) and 26% (95% CI 8%, 41%) lower H3N2 infection odds, respectively. Every fold increase in pre-existing seasonal H1N1 influenza A virus (sH1N1)-specific CD4 and CD8 T cells was associated with 28% (95% CI 11%, 41%) and 22% (95% CI 8%, 33%) lower pH1N1 infection odds, respectively. We observed the same associations for individuals with pre-epidemic hemagglutination inhibition (HAI) titers < 40. There was no correlation between pre-existing influenza virus-specific CD4 and CD8 T cell response and HAI titer.
Conclusions
We demonstrated homosubtypic and cross-strain protection against influenza infections was associated with T cell response, especially CD4 T cell response. These protections were independent of the protection associated with HAI titer. Therefore, T cell response could be an assessment of individual and population immunity for future epidemics and pandemics, in addition to using HAI titer.
... While heterosubtypic immunity against influenza is mainly mediated by cross-reactive cytotoxic T lymphocytes (CTLs), 44,45 which target conserved epitopes in the viral internal proteins such as nucleoprotein and matrix protein, [46][47][48] cross-reactive antibodies against HA and BnAbs have also been long reported, 34,49-52 with viral epitopes identified in either HA1 or HA2 or both. 32,33,53,54 BnAbs targeting HA1 mainly inhibit the viral replication through disrupting the binding of the HA protein with sialic acids receptor of the cells, while HA2-targeting BnAbs prevent viral entry through either hindering the pH-dependent conformational change or stabilizing the prefusion conformation of the HA protein. ...
... 32,33,53,54 BnAbs targeting HA1 mainly inhibit the viral replication through disrupting the binding of the HA protein with sialic acids receptor of the cells, while HA2-targeting BnAbs prevent viral entry through either hindering the pH-dependent conformational change or stabilizing the prefusion conformation of the HA protein. [32][33][34][46][47][48][49][50][51][52][55][56][57] Given the much higher conservation rates in the HA2, 26,58 BnAbs targeting the stem are more broadly reactive, with conformational epitopes found to involve at least three distinct parts of the HA protein, i.e. the HA1, HA2 and the fusion peptide at the N-terminus of the HA2 subunit. [32][33][34][58][59][60][61][62][63] In this brief communication, we further characterized Uni-1, a mono-specific antibody targeting the N-terminal 14-aa of the fusion peptide, which is the only universally conserved sequence among all influenza viruses. ...
Influenza is a major public health concern causing millions of hospitalizations every year. The current vaccines need annual updating based on prediction of likely strains in the upcoming season. However, mismatches between vaccines and the actual circulating viruses can occur, reducing vaccine effectiveness significantly because of the remarkably high rate of mutation in the viral glycoprotein, hemagglutinin (HA). Clearly, it would be of great interest to determine the potential role of universally conserved epitopes in inducing protective immunity. Here, an antibody against the 14-aa fusion peptide sequence at the N-terminus of the HA2 subunit (Uni-1) was investigated for its ability to elicit antibody-dependent cellular cytotoxicity (ADCC) in vitro and cross-protection against lethal infection in animals. Uni-1, known to neutralize influenza type A (IAV) in vitro, was found to induce strong ADCC against diverse influenza viruses, including human and avian IAVs and both lineages of type B (IBV). The ADCC effects against human IAVs by Uni-1 was comparable to ADCC induced by well-characterized antibodies, F10 and FI6V3. Importantly, mice treated with Uni-1 were protected against lethal challenge of IAV and IBV. These results revealed the versatile effector functions of this universal antibody against markedly diverse strains of both IAV and IBV.
... T cells might offer protection if H2N2 reemerges. The Cleveland Family study already reported in 1958 that prior exposure to H1N1 influenza resulted in reduced disease in participants infected with H2N2 11,12 . This was independent of neutralizing antibodies, hinting toward a role for T cells. ...
... By using both the ferret model and human blood donors, we partly mitigated the shortcomings that are associated with murine and human influenza studies. The Cleveland Family study which ran from 1947 to 1957 reported that adults pre-exposed to H1N1 displayed reduced H2N2 disease 11,12 . With our study we have clearly shown that H1N1 priming induces cross-reactive T cells and that they are associated with protection against H2N2 infection in ferrets. ...
Traditional influenza vaccines primarily induce a narrow antibody response that offers no protection against heterosubtypic infections. Murine studies have shown that T cells can protect against a broad range of influenza strains. However, ferrets are a more potent model for studying immune correlates of protection in influenza infection. We therefore set out to investigate the role of systemic and respiratory T cells in the protection against heterosubtypic influenza A infections in ferrets. H1N1-priming induced systemic and respiratory T cells that responded against pandemic H2N2 and correlated with reduced viral replication and disease. CD8-positive T cell responses in the upper and lower respiratory tract were exceptionally high. We additionally confirmed that H2N2-responsive T cells are present in healthy human blood donors. These findings underline the importance of the T cell response in influenza immunity and show that T cells are a potent target for future universal influenza vaccines.
... Cytotoxic T-lymphocyte (CTL) responses against peptidic epitopes of influenza's internal proteins can provide long-term protection (Van De Sandt et al., 2015) because these epitopes are highly conserved. Conserved T-cell epitopes are believed to be the cause of the relatively low illness severity in adults during the 2009 H1N1 pandemic (Sridhar et al., 2013), and the 1957 H2N2 pandemic (Epstein, 2006), although in both cases antibodies against the more conserved stem of HA could also have played a role. Not surprisingly, these T-cell epitopes are considered to be good targets for a long-lasting, universal vaccine (Berlanda Scorza et al., 2016;Sridhar, 2016). ...
... Individuals that do become infected, but experience mild disease (e.g. due to T-cell memory (Sridhar et al., 2013;Epstein, 2006)), are therefore not considered to be susceptible, and are assumed to be hardly infectious, due to limited viral shedding (Laurie et al., 2010). Notice that there is a slight mismatch between our interpretation of S 0 , and the usage of this parameter in the model. ...
The magnitude of influenza epidemics is largely determined by the number of susceptible individuals at the start of the influenza season. Susceptibility, in turn, is influenced by antigenic drift. The evolution of influenza’s B-cell epitopes has been charted thoroughly, and only recently evidence for T-cell driven evolution is accumulating. We investigate the relation between susceptibility to influenza, and antigenic drift at CD8 ⁺ T-cell epitopes over a 45-year timespan. We estimate age-specific susceptibility with data reported by general practitioners, using a disease-transmission model in a Bayesian framework. We find large variation in susceptibility, both between seasons and age classes. Although it is often assumed that antigenic drift drives the variation in susceptibility, we do not find evidence for a relation between drift and susceptibility in our data. This suggests that other factors determining the variation in susceptibility play a dominating role, or that complex influenza-infection histories obscure any direct effects.
Preface to this bioRχiv pre-print
We are currently in the process of making this manuscript ready for re-submission, and are resolving some issues brought forward by our referees. Most importantly, we aim to better incorporate the co-circulation of the various influenza A and B subtypes during the different seasons, both in the estimation of susceptibility and antigenic drift.
... Further, antibody responses against NA can be broadly protective [14][15][16] and have been implicated in protection against pandemic viruses [17]. In addition, it has been long suspected from epidemiological data that T-cell memory responses to conserved proteins of the virus (e.g., nucleoprotein NP, matrix M1 and M2e, and polymerase PB1) may also play an important role in pandemic protection [18]. A protective role of T-cell responses is supported by modern immunologic assays in humans [19,20] and epidemiological studies reporting how influenza T-cell escape variants can spread in populations [21]. ...
... cell or T cell mediated) and their impact on infection, disease, and transmission remains difficult to untangle [10,17,18,25,26,27,28]. As a case in point, following the 2009 influenza pandemic, seasonal H1N1 viruses were replaced by the new H1N1 pandemic virus, likely due to cross-immunity to conserved regions of these relatively distant viruses [11]. ...
The prospect of universal influenza vaccines is generating much interest and research at the intersection of immunology, epidemiology, and viral evolution. While the current focus is on developing a vaccine that elicits a broadly cross-reactive immune response in clinical trials, there are important downstream questions about global deployment of a universal influenza vaccine that should be explored to minimize unintended consequences and maximize benefits. Here, we review and synthesize the questions most relevant to predicting the population benefits of universal influenza vaccines and discuss how existing information could be mined to begin to address these questions. We review three research topics where computational modeling could bring valuable evidence: immune imprinting, viral evolution, and transmission. We address the positive and negative consequences of imprinting, in which early childhood exposure to influenza shapes and limits immune responses to future infections via memory of conserved influenza antigens. However, the mechanisms at play, their effectiveness, breadth of protection, and the ability to "reprogram" already imprinted individuals, remains heavily debated. We describe instances of rapid influenza evolution that illustrate the plasticity of the influenza virus in the face of drug pressure and discuss how novel vaccines could introduce new selective pressures on the evolution of the virus. We examine the possible unintended consequences of broadly protective (but infection-permissive) vaccines on the dynamics of epidemic and pandemic influenza, compared to conventional vaccines that have been shown to provide herd immunity benefits. In conclusion, computational modeling offers a valuable tool to anticipate the benefits of ambitious universal influenza vaccine programs, while balancing the risks from endemic influenza strains and unpredictable pandemic viruses. Moving forward, it will be important to mine the vast amount of data generated in clinical studies of universal influenza vaccines to ensure that the benefits and consequences of these vaccine programs have been carefully modeled and explored.
... They are followed by influenza-specific B and T cells that mediate the adaptive immune response (Fig.1). While antibody-mediated immunity is mainly strain-specific and can prevent infection, T cells (especially CD8 + T cells) provide broadly crossreactive cellular immunity against different influenza viruses and thus can ameliorate the severity of influenza disease [9][10][11][12][13]. Current vaccination strategies with inactivated influenza viruses induce strain-specific, B cell-based protective immunity directed against the viral hemagglutinin protein [14]. ...
... Individuals with demonstrable influenza-specific CD8 + T cell responses cleared the virus more efficiently, irrespective of the presence of pre-existing antibodies [9]. Subsequently, a retrospective report showed that individuals previously infected with H1N1 IAV in the 1950s were less susceptible to the 1957 H2N2 pandemic [10], further supporting the idea of heterosubtypic immunity that is presumed to be conferred by cellular immunity because antibodies elicited by H1N1 viruses do not protect against H2N2 IAV infection. The advent of the 2009 H1N1 pandemic provided further opportunities to determine the role of CD8 + T cells in protection against IAV infection. ...
Influenza is a major global health problem, causing infections of the respiratory tract, often leading to acute pneumonia, life-threatening complications and even deaths. Over the last seven decades, vaccination strategies have been utilized to protect people from complications of influenza, especially groups at high risk of severe disease. While current vaccination regimens elicit strain-specific antibody responses, they fail to generate cross-protection against seasonal, pandemic and avian viruses. Moreover, vaccines designed to generate influenza-specific T-cell responses are yet to be optimized. During natural infection, viral replication is initially controlled by innate immunity before adaptive immune responses (T cells and antibody-producing B cells) achieve viral clearance and host recovery. Adaptive T and B cells maintain immunological memory and provide protection against subsequent infections with related influenza viruses. Recent studies also shed light on the role of innate T-cells (MAIT cells, γδ cells, and NKT cells) in controlling influenza and linking innate and adaptive immune mechanisms, thus making them attractive targets for vaccination strategies. We summarize the current knowledge on influenza-specific innate MAIT and γδ T cells as well as adaptive CD8⁺ and CD4⁺ T cells, and discuss how these responses can be harnessed by novel vaccine strategies to elicit cross-protective immunity against different influenza strains and subtypes.
... The predominant H3N2 NP-specific T cell responses during seasonal and pandemic flu outbreaks during 2006 to 2010 were associated with robust cross-protection in the absence of protective antibody responses [3]. A cross-reactive cluster of differentiation 8 positive T-lymphocyte (CD8 + T cell) response has a significant protective role in heterologous clinical and preclinical prime/challenge studies between H1N1, H7N7, H5N1, and H3N2 influenza viruses [5][6][7][8]. Furthermore, a universal influenza vaccine candidate in pigs mitigated the lung pathology and reduced the nasal and lung viral load of homologous and heterologous challenge viruses in the absence of neutralizing antibodies [9]. ...
Swine influenza A viruses (SwIAVs) are pathogens of both veterinary and medical significance. Intranasal (IN) vaccination has the potential to reduce flu infection. We investigated the efficacy of split SwIAV H1N2 antigens adsorbed with a plant origin nanoparticle adjuvant [Nano11–SwIAV] or in combination with a STING agonist ADU-S100 [NanoS100–SwIAV]. Conventional pigs were vaccinated via IN and challenged with a heterologous SwIAV H1N1-OH7 or 2009 H1N1 pandemic virus. Immunologically, in NanoS100–SwIAV vaccinates, we observed enhanced frequencies of activated monocytes in the blood of the pandemic virus challenged animals and in tracheobronchial lymph nodes (TBLN) of H1N1-OH7 challenged animals. In both groups of the virus challenged pigs, increased frequencies of IL-17A+ and CD49d+IL-17A+ cytotoxic lymphocytes were observed in Nano11–SwIAV vaccinates in the draining TBLN. Enhanced frequency of CD49d+IFNγ+ CTLs in the TBLN and blood of both the Nano11-based SwIAV vaccinates was observed. Animals vaccinated with both Nano11-based vaccines had upregulated cross-reactive secretory IgA in the lungs and serum IgG against heterologous and heterosubtypic viruses. However, in NanoS100–SwIAV vaccinates, a slight early reduction in the H1N1 pandemic virus and a late reduction in the SwIAV H1N1-OH7 load in the nasal passages were detected. Hence, despite vast genetic differences between the vaccine and both the challenge viruses, IN vaccination with NanoS100–SwIAV induced antigen-specific moderate levels of cross-protective immune responses.
... The priming of universally protective immunity against IAV through vaccination is a high priority. An attractive means to generate such immunity is through the induction of IAV-specific memory T cells that have been shown in animal and clinical studies to mediate robust protection against IAV-induced disease (8,1316,67). A major hurdle for stimulating robust T cell memory through vaccination is the presence of pre-existing pathogen-specific immunity (68,69), which can likewise hinder the capacity to stimulate the generation of Ab responses from B cells recognizing novel viral epitopes (25,70). ...
Overcoming interfering impacts of pre-existing immunity to generate universally protective influenza A virus (IAV)-specific T cell immunity through vaccination is a high priority. In this study, we passively transfer varied amounts of H1N1-IAV-specific immune serum before H1N1-IAV infection to determine how different levels of pre-existing Ab influence the generation and protective potential of heterosubtypic T cell responses in a murine model. Surprisingly, IAV nucleoprotein-specific CD4 and CD8 T cell responses are readily detected in infected recipients of IAV-specific immune serum regardless of the amount transferred. When compared with responses in control groups and recipients of low and intermediate levels of convalescent serum, nucleoprotein-specific T cell responses in recipients of high levels of IAV-specific serum, which prevent overt weight loss and reduce peak viral titers in the lungs, are, however, markedly reduced. Although detectable at priming, this response recalls poorly and is unable to mediate protection against a lethal heterotypic (H3N2) virus challenge at later memory time points. A similar failure to generate protective heterosubtypic T cell immunity during IAV priming is seen in offspring of IAV-primed mothers that naturally receive high titers of IAV-specific Ab through maternal transfer. Our findings support that priming of protective heterosubtypic T cell responses can occur in the presence of intermediate levels of pre-existing Ab. These results have high relevance to vaccine approaches aiming to incorporate and evaluate cellular and humoral immunity towards IAV and other viral pathogens against which T cells can protect against variants escaping Ab-mediated protection.
... A universal next-generation vaccinia vectored vaccine candidate, MVA-NP+M1, currently in phase 2b trials (5), has been shown to boost T cell responses, including in adults more than 65 years of age, and led to reduced infection and viral shedding (6). As cross-reactive T cells toward H5N1, H7N9, and pandemic H1N1 viruses can be found in the majority of healthy unexposed individuals (7,8), these responses could be boosted or established by next-generation T cell-activating vaccines potential for improved breadth of protection against diverse influenza viruses. ...
To determine the potential for viral adaptation to T cell responses, we probed the full influenza virus genome by next-generation sequencing directly ex vivo from infected mice, in the context of an experimental T cell-based vaccine, an H5N1-based viral vectored vaccinia vaccine Wyeth/IL-15/5Flu, versus the current standard-of-care, seasonal inactivated influenza vaccine (IIV) and unvaccinated conditions. Wyeth/IL-15/5Flu vaccination was coincident with increased mutation incidence and frequency across the influenza genome; however, mutations were not enriched within T cell epitope regions, but high allele frequency mutations within conserved hemagglutinin stem regions and PB2 mammalian adaptive mutations arose. Depletion of CD4+ and CD8+ T cell subsets led to reduced frequency of mutants in vaccinated mice; therefore, vaccine-mediated T cell responses were important drivers of virus diversification. Our findings suggest that Wyeth/IL-15/5Flu does not generate T cell escape mutants but increases stochastic events for virus adaptation by stringent bottlenecks.
... The Tecumseh Study examined illness duration and the age-related factors driving this from 1965 to 1972 and 1976 to 1981, identifying age-specific infection rates and peak ages for influenza A and B infection 12 . The Cleveland and Houston family cohorts both conducted household-based studies to track outbreaks and characterize the incidence and noted the presence of protection from re-infection in some seasons but not others [13][14][15] . While these historical studies laid important groundwork for the examination of homotypic protection, they were limited in both power and by the laboratory techniques of the time, which restricted the ability to time infection events precisely. ...
The period of protection from repeat infection following symptomatic influenza is not well established due to limited availability of longitudinal data. Using data from a pediatric cohort in Managua, Nicaragua, we examine the effects of natural influenza virus infection on subsequent infection with the same influenza virus subtype/lineage across multiple seasons, totaling 2,170 RT-PCR-confirmed symptomatic influenza infections. Logistic regression models assessed whether infection in the prior influenza season protected against homologous reinfection. We sequenced viruses from 2011–2019 identifying dominant clades and measuring antigenic distances between hemagglutinin clades. We observe homotypic protection from repeat infection in children infected with influenza A/H1N1pdm (OR 0.12, CI 0.02–0.88), A/H3N2 (OR 0.41, CI 0.24–0.73), and B/Victoria (OR 0.00, CI 0.00–0.14), but not with B/Yamagata viruses (OR 0.60, CI 0.09–2.10). Overall, protection wanes as time or antigenic distance increases. Individuals infected with one subtype or lineage of influenza virus have significantly lower odds of homologous reinfection for the following one to two years; after two years this protection wanes. This protection is demonstrated across multiple seasons, subtypes, and lineages among children. Here Wraith et al. report homotypic protection from repeated influenza infection in a prospective pediatric cohort in Nicaragua followed for 9 years. This protection is observed across multiple seasons, subtypes, and lineages and is consistent for older and younger children.
... Although influenza-specific cytotoxic CD8 + T cells cannot prevent infection, as they only act upon virus-infected cells, the presence of these cells has been shown to be associated with better prognosis following influenza virus infection. As such, vaccines with the capacity to establish a pool of memory cross-reactive CD8 + T cells have the potential to be "universal" vaccines, that is those providing broad coverage against heterologous influenza A virus strains, including those of different subtypes [90][91][92]. The importance of CD8 + T cell responses in resolving influenza virus infection is illustrated in a study of zoonotic H7N9 infections in humans, where Wang et al. [93] found that the presence of an early CD8 + T cell response, indicative of activation and expansion of pre-existing cross-protective memory cells, correlated with faster recovery and less severe disease. ...
Despite seasonal influenza vaccines having been routinely used for many decades, influenza A virus continues to pose a global threat to humans, causing high morbidity and mortality each year. The effectiveness of the vaccine is largely dependent on how well matched the vaccine strains are with the circulating influenza virus strains. Furthermore, low vaccine efficacy in naïve populations such as young children, or in the elderly, who possess weakened immune systems, indicates that influenza vaccines need to be more personalized to provide broader community protection. Advances in both vaccine technologies and our understanding of influenza virus infection and immunity have led to the design of a variety of alternate vaccine strategies to extend population protection against influenza, some of which are now in use. In this review, we summarize the progress in the field of influenza vaccines, including the advantages and disadvantages of different strategies, and discuss future prospects. We also highlight some of the challenges to be faced in the ongoing effort to control influenza through vaccination.
... Based on human studies of natural and experimental influenza virus infection, it is well-established that in the absence of neutralizing antibodies, pre-existing memory CD8 + T cells and CD4 + T cells can reduce disease severity [5][6][7][8][9][10][11][12][13][14] . Published evidence also associates genetic host factors, such as specific HLA types and interferon-induced transmembrane protein 3 (IFITM3) singlenucleotide polymorphisms (SNPs) with clinically poor outcomes [15][16][17][18][19] . ...
How innate and adaptive immune responses work in concert to resolve influenza disease is yet to be fully investigated in one single study. Here, we utilize longitudinal samples from patients hospitalized with acute influenza to understand these immune responses. We report the dynamics of 18 important immune parameters, related to clinical, genetic and virological factors, in influenza patients across different severity levels. Influenza disease correlates with increases in IL-6/IL-8/MIP-1α/β cytokines and lower antibody responses. Robust activation of circulating T follicular helper cells correlates with peak antibody-secreting cells and influenza heamaglutinin-specific memory B-cell numbers, which phenotypically differs from vaccination-induced B-cell responses. Numbers of influenza-specific CD8 ⁺ or CD4 ⁺ T cells increase early in disease and retain an activated phenotype during patient recovery. We report the characterisation of immune cellular networks underlying recovery from influenza infection which are highly relevant to other infectious diseases.
... These events are characterized by different distributions of age risk: an initial pandemic wave may be dominated by morbidity among school-aged children, and some empirical and modeling studies suggest that adults are more likely to become infected in the season following a pandemic [9,10,11,12,13]. While the mechanisms for this remain poor understood, it has been suggested that there is an accumulation of heterologous immunity with age [49]. Additionally, it has been observed that excess P&I mortality shifts from the elderly to younger ages in the years following a pandemic, perhaps signaling shifted dynamics between children and adults during this time as well. ...
Background: Measures of population-level influenza severity are important for public health planning, but estimates are often based on case-fatality and case-hospitalization risks, which require multiple data sources, are prone to surveillance biases, and are typically unavailable in the early stages of an outbreak. In this study, we develop a severity index based on influenza age dynamics estimated from routine surveillance data that can be used in retrospective and early warning contexts. Methods and Findings: Our method relies on the observation that age-specific attack rates vary between seasons, so that key features of the age distribution of cases may be used as a marker of severity early in an epidemic. We illustrate our method using weekly outpatient medical claims of influenza-like illness (ILI) in the United States from the 2001 to 2009 and develop a novel population-level influenza severity index based on the relative risk of ILI among working-age adults to that among school-aged children. We validate our ILI index against a benchmark that comprises traditional influenza severity indicators such as viral activity, hospitalizations and deaths using publicly available surveillance data. We find that severe influenza seasons have higher relative rates of ILI among adults than mild seasons. In reference to the benchmark, the ILI index is a robust indicator of severity during the period of peak epidemic growth (87.5% accuracy in retrospective classification), and may have predictive power during the period between Thanksgiving and the winter holidays (57.1% accuracy in early warning). We further apply our approach at the state-level to characterize regional severity patterns across seasons. We hypothesize that our index is a proxy for severity because working-age adults have both pre-existing immunity to influenza and a high number of contacts, infecting them preferentially in severe seasons associated with antigenic changes in circulating influenza viruses. Our analysis is limited by its application to seasonal influenza epidemics and a relatively short study period. Conclusions: Our severity index and research on the link between age dynamics and seasonal influenza severity will enable decision makers to better target public health strategies in severe seasons and improve our knowledge of influenza epidemiology and population impact. These findings demonstrate that routine surveillance data can be translated into operational information for policymakers. Our study also highlights the need for further research on the putative age-related mechanisms of severity in seasonal and pandemic influenza seasons.
... T cells specific to the conserved viral epitopes have been evidenced to provide crossprotection across IAV, IBV and ICV (McMichael et al. 1983;Greenbaum et al. 2009;Gras et al. 2010;Sridhar et al. 2013;Quinones-Parra et al. 2014;Hayward et al. 2015;Wang et al. 2015Wang et al. , 2018Koutsakos et al. 2019). Moreover, pre-existing T cell responses have been demonstrated to correlate with protection from influenza disease in humans by epidemiological studies (Epstein 2006;Hayward et al. 2015). The antigenic origin of these broadly cross-reactive epitopes is therefore of great interest in the development of CD8 ? ...
Conventional influenza vaccines are based on predicting the circulating viruses year by year, conferring limited effectiveness since the antigenicity of vaccine strains does not always match the circulating viruses. This necessitates development of universal influenza vaccines that provide broader and lasting protection against pan-influenza viruses. The discovery of the highly conserved immunogens (epitopes) of influenza viruses provides attractive targets for universal vaccine design. Here we review the current understanding with broadly protective immunogens (epitopes) and discuss several important considerations to achieve the goal of universal influenza vaccines.
... It is known that pre-existing immunity toward influenza virus contributes to protection during re-infection in later seasons with an influenza virus of a different subtype (heterosubtypic immunity, HSI). Repeated exposure to influenza virus in humans has been shown to correlate with protection from severe disease during re-exposure to a different subtype of influenza virus (3). Both virus-induced humoral and cellular adaptive immune responses can contribute to such heterosubtypic immunity (4)(5)(6)(7)(8). ...
Conventional influenza vaccines aim at the induction of virus-neutralizing antibodies that provide with sterilizing immunity. However, influenza vaccination often confers protection from disease but not from infection. The impact of infection-permissive vaccination on the immune response elicited by subsequent influenza virus infection is not well-understood. Here, we investigated to what extent infection-permissive immunity, in contrast to virus-neutralizing immunity, provided by a trivalent inactivated virus vaccine (TIV) modulates disease and virus-induced host immune responses after sublethal vaccine-matching H1N1 infection in a mouse model. More than one TIV vaccination was needed to induce a serum HI titer and provide sterilizing immunity upon homologous virus infection. However, single TIV administration provided infection-permissive immunity, characterized by lower viral lung titers and faster recovery. Despite the presence of replicating virus, single TIV vaccination prevented induction of pro-inflammatory cyto- and chemokines, alveolar macrophage depletion as well as the establishment of lung-resident B and T cells after infection. To investigate virus infection-induced cross-protective heterosubtypic immune responses in vaccinated and unvaccinated animals, mice were re-infected with a lethal dose of H3N2 virus 4 weeks after H1N1 infection. Single TIV vaccination did not prevent H1N1 virus infection-induced heterosubtypic cross-protection, but shifted the mechanism of cross-protection from the cellular to the humoral branch of the immune system. These results suggest that suboptimal vaccination with conventional influenza vaccines may still positively modulate disease outcome after influenza virus infection, while promoting humoral heterosubtypic immunity after virus infection.
... The study demonstrated influenza-specific CTL in the Eijkman Institute for Molecular Biology, Jl. Diponegoro 69, Jakarta 10430, Indonesia Email address: marsia@eijkman.go.id absence of cross-protective antibody rapidly cleared infection and reduced disease to subclinical levels. The Cleveland family study showed that during the H2N2 pandemic of 1957, individuals that had experienced H1N1 influenza A were less likely to develop severe disease or succumb to infection with H2N2 [2]. ...
... Viral Immunology Section, NIAID, NIH, Bethesda, Maryland. However, CD8+ T cells have been shown in animal models to definitively provide protection against IAV disease, and a beneficial role has been suggested in human studies (10,11). The greatest benefit for T cell immunity has been argued for the case of novel pandemic IAV infections where preexisting B cell immunity is lacking. ...
... No decay of antibody-based immunity against measles and mumps was observed, suggesting a life-long protection after recovery from primary infections from these viruses (11). Also, the contrasted fractions of adults, previously exposed to different influenza viruses, and children, developing influenza during the 1957 pandemic, suggests that accumulated heterosubtypic immunity largely influences the antibody dependent protection (12). However, the longevity of antibody memory and the magnitude of associated anamnestic responses is heterogeneous across individuals (13), and pathogen dependent. ...
Long-term immunity is of great importance for protection against pathogens and has been extensively studied in mammals. Successive heterologous infections can affect the maintenance of immune memory, inducing attrition of T memory cells and diminishing B cell mediated protection. In fish, the basis of immune memory and the mechanisms of immunization to heterologous pathogens remain poorly understood. We sequentially immunized isogenic rainbow trout with two immunologically distinct viruses, VHSV and IPNV, either with one virus only or in combination, and analyzed the antibody responses and repertoires. Neutralizing antibodies and ELISPOT did not reveal an effect of heterologous immunization. Using a consensus read sequencing approach that incorporates unique barcodes to each cDNA molecule, we focused on the diversity expressed by selected responding VH/C combinations. We identified both public and private responses against VHSV and/or IPNV in all groups of fish. In fish immunized with two viruses, we registered no significant reduction in the persistence of the response toward the primary immunization. Similarly, the response to the second immunization was not affected by a prior vaccination to the other virus. Our data suggest that heterologous immunization does not enforce attrition of pre-existing antibody producing cells, which may impair the protection afforded by multiple successive vaccinations. These observations are potentially important to improve vaccination strategies practiced in aquaculture.
... T cells recognizing these antigens can be detected in most adults and are cross-reactive to influenza A virus subtypes to which the donors have not been previously exposed (17,18). Indeed, epidemiology studies have demonstrated correlations between pre-existing T cell responses and protection from influenza disease in humans (19,20). These studies suggest that a vaccine that primes or boosts a T cell response against highly conserved internal antigens could induce heterosubtypic protection against influenza viruses. ...
Seasonal influenza viruses cause significant morbidity and mortality in the global population every year. Although seasonal vaccination limits disease, mismatches between the circulating strain and the vaccine strain can severely impair vaccine effectiveness. Because of this, there is an urgent need for a universal vaccine that induces broad protection against drifted seasonal and emerging pandemic influenza viruses. Targeting the conserved stalk region of the influenza virus hemagglutinin (HA), the major glycoprotein on the surface of the virus, results in the production of broadly protective antibody responses. Furthermore, replication deficient viral vectors based on Chimpanzee Adenovirus Oxford 1 (ChAdOx1) and modified vaccinia Ankara (MVA) virus expressing the influenza virus internal antigens, the nucleoprotein (NP) and matrix 1 (M1) protein, can induce strong heterosubtypic influenza virus-specific T cell responses in vaccinated individuals. Here, we combine these two platforms to evaluate the efficacy of a viral vectored vaccination regimen in protecting ferrets from H3N2 influenza virus infection. We observed that viral vectored vaccines expressing both stalk-targeting, chimeric HA constructs, and the NP+M1 fusion protein, in a prime-boost regimen resulted in the production of antibodies toward group 2 HAs, the HA stalk, NP and M1, as well as in induction of influenza virus-specific—IFNγ responses. The immune response induced by this vaccination regime ultimately reduced viral titers in the respiratory tract of influenza virus infected ferrets. Overall, these results improve our understanding of vaccination platforms capable of harnessing both cellular and humoral immunity with the goal of developing a universal influenza virus vaccine.
... T cells have the ability to provide broad protection against diverse influenza strains in mice [5][6][7] and in humans [8][9][10][11][12]. However, to date, no influenza vaccines are available for inducing influenza-specific T cell-mediated heterotypic immunity in humans, despite the potential for this strategy to greatly improve influenza vaccine-induced immunity. ...
Influenza world-wide causes significant morbidity and mortality annually, and more severe pandemics when novel strains evolve to which humans are immunologically naïve. Because of the high viral mutation rate, new vaccines must be generated based on the prevalence of circulating strains every year. New approaches to induce more broadly protective immunity are urgently needed. Previous research has demonstrated that influenza-specific T cells can provide broadly heterotypic protective immunity in both mice and humans, supporting the rationale for developing a T cell-targeted universal influenza vaccine. We used state-of-the art immunoinformatic tools to identify putative pan-HLA-DR and HLA-A2 supertype-restricted T cell epitopes highly conserved among > 50 widely diverse influenza A strains (representing hemagglutinin types 1, 2, 3, 5, 7 and 9). We found influenza peptides that are highly conserved across influenza subtypes that were also predicted to be class I epitopes restricted by HLA-A2. These peptides were found to be immunoreactive in HLA-A2 positive but not HLA-A2 negative individuals. Class II-restricted T cell epitopes that were highly conserved across influenza subtypes were identified. Human CD4+ T cells were reactive with these conserved CD4 epitopes, and epitope expanded T cells were responsive to both H1N1 and H3N2 viruses. Dendritic cell vaccines pulsed with conserved epitopes and DNA vaccines encoding these epitopes were developed and tested in HLA transgenic mice. These vaccines were highly immunogenic, and more importantly, vaccine-induced immunity was protective against both H1N1 and H3N2 influenza challenges. These results demonstrate proof-of-principle that conserved T cell epitopes expressed by widely diverse influenza strains can induce broadly protective, heterotypic influenza immunity, providing strong support for further development of universally relevant multi-epitope T cell-targeting influenza vaccines.
... During the twentieth century, type A influenza viruses caused three massive global pandemics: 1918 (H1N1), 1957 (H2N2) and 1968 (H3N2) [1][2][3]. A fourth type A influenza pandemic took place in 2009 [4]. ...
Avian influenza viruses (AIVs) are a continued threat to global health and economy. Unlike other highly pathogenic AIVs, novel H5N8 disseminated very quickly from Korea to other areas in Asia, Europe and even North America following its first outbreak in 2014. However, the pathobiological features of the virus that favoured its global translocation remain unknown. In this study, we used a compartmental model to examine the avian epidemiological characteristics that would support the geographical spread of influenza by bird migration, and to provide recommendations for AIV surveillance in wild bird populations. We simulated virus transmission and translocation in a migratory bird population while varying four system properties: (i) contact transmission rate; (ii) infection recovery rate; (iii) mortality rate induced by infection; and (iv) migratory recovery rate. Using these simulations, we then calculated extinction and translocation probabilities for influenza during spring migration as a function of the altered properties. We find that lower infection recovery rates increase the likelihood of AIV translocation in migratory bird populations. In addition, lower mortality rates or migration recovery rates also favour translocation. Our results identify pathobiological features supporting AIV intercontinental dissemination risk and suggest that characteristic differences exist among H5N8 and other AIV subtypes that have not translocated as rapidly (e.g. H5N6 and H5N1).
... After the Influenza virus is cleared, antigen specific memory CD8 + T cells are long-lived and are capable of rapid recall to effector function. Evidence 10,11 suggests that CD8 + T-cells mediate cross-reactive protection in the face of heterologous prime/challenge among H1N1, H2N2, H3N2 and H5N1 viruses. However, neutralizing antibodies generated against HA can protect from infection with a specific strain, and these antibody responses are generally not cross-reactive with other influenza strains 12 . ...
Avian Influenza A (H5N6) Virus causes severe influenza disease in humans and is manifested by acute respiratory distress syndrome, multi-organ failure, and high mortality rates. T cells recognize antigens specifically through a membrane protein T cell receptor (TCR). To ward off a wide variety of pathogens, the human adaptive immune system harbors a vast array of TCRs, which are collectively referred to as the TCR repertoire. The B cell receptor (BCR) is involved in inducing the humoral immune response. The generation of a diverse T cell and B cell repertoire is essential for protection against infection. In this study, multiplex PCR based on genomic DNA amplicons and Illumina high-throughput sequencing (HTS) were applied to study the characteristics and polymorphisms of the TRB and IGH repertoire in the peripheral blood mononuclear cells (PBMCs) from two H5N6 AIV patients and six healthy donors (NC). The CDR3 average length in the AIV group was different from the NC group. The TRBV12-3, TRBV12-4, and TRBV15 gene segments and TRBV30/TRBJ1-2, TRBV12-3/TRBJ1-1 and IGHV3-11/IGHJ6 gene segment pairings also exhibited a higher usage in the PBMCs of AIV donors and may provide more information for generating more effective T/B cell targeted diagnosis/protection strategies.
... Possibly, anti-M2e-IgG immune-complexes are also recognized by dendritic cells, which thereby can take up, process and present virus-containing cell fractions to T cells in the draining lymph nodes. T cell responses directed against the conserved internal influenza gene products are important because they are associated with broad protection38 . Secondly, M2e-specific CD4 + T cells can contribute to protection in their own right, but also stimulate HA-specific antibodies upon challenge virus infection39 . ...
The influenza A virus matrix protein 2 ectodomain (M2e) is a universal influenza A vaccine candidate. Numerous studies in laboratory mice, but very few in natural influenza A virus hosts, have demonstrated that M2e-based vaccines can provide protection against any influenza A virus challenge. M2e-based immunity is largely accomplished by IgG and early stage clinical studies have demonstrated that the vaccine is safe. Yet M2e is considered a difficult target to develop as a vaccine: it does not offer sterilizing immunity and its mode of action relies on Fcγ receptor-mediated effector mechanisms, most likely in concert with alveolar macrophages. In a human challenge study with an H3N2 virus, treatment with a monoclonal M2e-specific human IgG was associated with a faster recovery compared to placebo treatment. If the universal influenza vaccine field incorporates this antigen into next generation vaccines, M2e could prove its merit when the next influenza pandemic strikes.
... 5 Nonetheless, a vaccine approach based on cellular responses to conserved internal antigens could minimize the effects of antigenic drift and even mismatches. Influenza pandemics are very informative in this respect: in a retrospective serological study 6 of the H2N2 pandemic of 1957, suggestive evidence was found that adults exposed to the new virus were spared from influenza more frequently than children. The author proposed that the main protective factor in adults was immunity resulting from prior infection with earlier (non-H2N2) strains. ...
Influenza vaccine: engineered nucleoprotein with improved protective efficacy against multiple strains
Circulating influenza A virus (IAV) strains differ in their surface proteins each year, and vaccines eliciting an immune response to these proteins are often only partially protective. Internal viral proteins, such as the nucleoprotein (NP), are highly conserved, and cellular immunity to NP has been correlated with protection from diverse strains. However, current IAV vaccines induce a poor immune response to NP. In this study, led by Fergal Hill from Osivax, researchers develop an oligomeric version of NP with improved immunogenicity. Vaccination of mice with oligomeric NP results in an improved NP-specific T-cell response, including CD8⁺ tissue memory T cells in the lung, and protects mice against three different IAV subtypes. Co-administration with the currently used inactivated influenza vaccine further improves protection against virus infection in mice. These results encourage further pre-clinical and clinical development for this vaccine candidate.
... Since these internal proteins do not undergo rapid antigenic change, CD8 + T cells are able to provide cross-protection against a broad range of different influenza virus strains. Accordingly, pre-existing influenza virus specific CD8 + T cells provided protection against severe disease during the influenza pandemics of both 1957 and 2009 (Slepushkin, 1959;McMichael et al., 1983;Epstein, 2006;Sridhar et al., 2013;Hayward et al., 2015). In addition, seasonally induced influenza virus-specific CD8 + T cells can cross-react with novel potentially pandemic avian influenza viruses (Kreijtz et al., 2008;Lee et al., 2008;van de Sandt et al., 2014) and facilitate more rapid recovery in patients following infection with low pathogenic H7N9 avian influenza virus . ...
2018 marks the 100-year anniversary of the 1918 influenza pandemic, which killed ~50 million people worldwide. The severity of this pandemic resulted from a complex interplay between viral, host, and societal factors. Here, we review the viral, genetic and immune factors that contributed to the severity of the 1918 pandemic and discuss the implications for modern pandemic preparedness. We address unresolved questions of why the 1918 influenza H1N1 virus was more virulent than other influenza pandemics and why some people survived the 1918 pandemic and others succumbed to the infection. While current studies suggest that viral factors such as haemagglutinin and polymerase gene segments most likely contributed to a potent, dysregulated pro-inflammatory cytokine storm in victims of the pandemic, a shift in case-fatality for the 1918 pandemic toward young adults was most likely associated with the host's immune status. Lack of pre-existing virus-specific and/or cross-reactive antibodies and cellular immunity in children and young adults likely contributed to the high attack rate and rapid spread of the 1918 H1N1 virus. In contrast, lower mortality rate in in the older (>30 years) adult population points toward the beneficial effects of pre-existing cross-reactive immunity. In addition to the role of humoral and cellular immunity, there is a growing body of evidence to suggest that individual genetic differences, especially involving single-nucleotide polymorphisms (SNPs), contribute to differences in the severity of influenza virus infections. Co-infections with bacterial pathogens, and possibly measles and malaria, co-morbidities, malnutrition or obesity are also known to affect the severity of influenza disease, and likely influenced 1918 H1N1 disease severity and outcomes. Additionally, we also discuss the new challenges, such as changing population demographics, antibiotic resistance and climate change, which we will face in the context of any future influenza virus pandemic. In the last decade there has been a dramatic increase in the number of severe influenza virus strains entering the human population from animal reservoirs (including highly pathogenic H7N9 and H5N1 viruses). An understanding of past influenza virus pandemics and the lessons that we have learnt from them has therefore never been more pertinent.
... Evidence has accumulated, some suggestive and some more definite, that immunity due to previous influenza exposures can protect humans against a novel strain despite absence of neutralizing antibodies to it (133)(134)(135). Because of prior infections, humans have readily detectable immune memory responses to conserved influenza virus antigens, including T-cell responses to NP, M1, PB1, and other antigens (26,27,136,137); and antibodies to M2 (69, 138), NP (69), and the HA stem (61, 139). ...
Despite all we have learned since 1918 about influenza virus and immunity, available influenza vaccines remain inadequate to control outbreaks of unexpected strains. Universal vaccines not requiring strain-matching would be a major improvement. Their composition would be independent of predicting circulating viruses, and thus potentially effective against unexpected drift or pandemic strains. This commentary explores progress with candidate universal vaccines based on various target antigens. Candidates include vaccines based on conserved viral proteins such as nucleoprotein and matrix, on the conserved hemagglutinin (HA) stem, and various combinations. Discussion will cover the differing evidence for each candidate vaccine demonstrating protection in animals against influenza viruses of widely divergent HA subtypes and groups, durability of protection, routes of administration including mucosal providing local immunity, and reduction of transmission. Human trials of some candidate universal vaccines have been completed or are underway. Interestingly, the HA stem, like nucleoprotein and matrix, induces immunity permitting some virus replication and emergence of escape mutants fit enough to cause disease. Vaccination with multiple target antigens will thus have advantages over use of single antigens. Ultimately, a universal vaccine providing long-term protection against all influenza virus strains might contribute to pandemic control and routine vaccination.
... Epidemiological studies during past influenza pandemics, where there is an absence of neutralizing antibodies, have suggested that T cell-mediated immunity provided some heterosubtypic protection [90][91][92]. However, the complexity involved in conducting such studies (i.e., obtaining the right cohort that does not have pre-existing antibody response and sampling prior to infection) means that direct evidence for the role of T cells during influenza virus infections in humans has been limited. ...
Next-generation vaccines that utilize T cells could potentially overcome the limitations of current influenza vaccines that rely on antibodies to provide narrow subtype-specific protection and are prone to antigenic mismatch with circulating strains. Evidence from animal models shows that T cells can provide heterosubtypic protection and are crucial for immune control of influenza virus infections. This has provided hope for the design of a universal vaccine able to prime against diverse influenza virus strains and subtypes. However, multiple hurdles exist for the realisation of a universal T cell vaccine. Overall primary concerns are: extrapolating human clinical studies, seeding durable effective T cell resident memory (Trm), population human leucocyte antigen (HLA) coverage, and the potential for T cell-mediated immune escape. Further comprehensive human clinical data is needed during natural infection to validate the protective role T cells play during infection in the absence of antibodies. Furthermore, fundamental questions still exist regarding the site, longevity and duration, quantity, and phenotype of T cells needed for optimal protection. Standardised experimental methods, and eventually simplified commercial assays, to assess peripheral influenza-specific T cell responses are needed for larger-scale clinical studies of T cells as a correlate of protection against influenza infection. The design and implementation of a T cell-inducing vaccine will require a consensus on the level of protection acceptable in the community, which may not provide sterilizing immunity but could protect the individual from severe disease, reduce the length of infection, and potentially reduce transmission in the community. Therefore, increasing the standard of care potentially offered by T cell vaccines should be considered in the context of pandemic preparedness and zoonotic infections, and in combination with improved antibody vaccine targeting methods. Current pandemic vaccine preparedness measures and ongoing clinical trials under-utilise T cell-inducing vaccines, reflecting the myriad questions that remain about how, when, where, and which T cells are needed to fight influenza virus infection. This review aims to bring together basic fundamentals of T cell biology with human clinical data, which need to be considered for the implementation of a universal vaccine against influenza that harnesses the power of T cells.
... Nevertheless, prior infection may confer partial, or cross, immunity to future infection and lead to competing interactions among influenza viruses. Animal experiments and serological surveys have shown that cross-immunity exists, not only in influenza strains of the same subtype but also across subtypes [27][28][29][30][31][32][33][34][35] and types [36][37][38] . Here we showed that interactions among the three influenza (sub)types are a key determinant of the epidemic dynamics of individual (sub)types. ...
Background
The association of influenza with meteorological variables in tropical climates remains controversial. Here we investigate the impact of weather conditions on influenza in the tropics and factors that may contribute to this uncertainty.
Methods
We computed the monthly viral positive rate for each of the three circulating influenza (sub)types (i.e., A/H1N1, A/H3N2, and B) among patients presenting with influenza‐like illness (ILI) or severe acute respiratory infections (SARI) in two Ugandan cities (Entebbe and Kampala). Using this measure as a proxy for influenza activity, we applied regression models to examine the impact of temperature, relative humidity, absolute humidity, and precipitation, as well as interactions among the three influenza viruses on the epidemic dynamics of each influenza (sub)type. A full analysis including all four weather variables was done for Entebbe during 2007‐2015 and a partial analysis including only temperature and precipitation was done for both cities during 2008‐2014.
Results
For Entebbe, the associations with weather variables differed by influenza (sub)type; with adjustment for viral interactions, the models showed that precipitation and temperature were negatively correlated with A/H1N1 activity, but not for A/H3N2 or B. A mutually negative association between A/H3N2 and B activity was identified in both Entebbe and Kampala.
Conclusion
Our findings suggest that key interactions exist among influenza (sub)types at the population level in the tropics and that such interactions can modify the association of influenza activity with weather variables. Studies of the relationship between influenza and weather conditions should therefore determine and account for co‐circulating influenza (sub)types.
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... These findings suggest that there are likely strong epidemic interactions among the three influenza (sub)types at the population level. These viral interactions are likely a result of cross-immunity conferred by prior infections of antigenically similar strains (Bodewes et al., 2011;Ekiert et al., 2009;Ekiert et al., 2011;Epstein, 2006;Katz et al., 2009;McMichael et al., 1983;Miller et al., 2012;Pica and Palese, 2013;Sandbulte et al., 2007) and types (Dreyfus et al., 2012;Laurie et al., 2016;Stanekova and Vareckova, 2010). ...
In this paper, we report the epidemic characteristics of the three co-circulating influenza viruses (i.e., A/H1N1, A/H3N2, and B) in two tropical African cities-Kampala and Entebbe, Uganda-over an eight-year period (2008-2015). Using wavelet methods, we show that influenza epidemics recurred annually during the study period. In most months, two or more influenza viruses co-circulated at the same time. However, the epidemic timing differed by influenza (sub)type. Influenza A/H3N2 caused epidemics approximately every 2 years in both cities and tended to alternate with A/H1N1 or B. Influenza A/H1N1 and B produced smaller but more frequent epidemics and biennial epidemics of these two viruses tended to be synchronous. In addition, epidemics of A/H3N2 were more synchronized in the two cities (located ca.37 km apart) than that of A/H1N1 or influenza B.
... Influenza infected women without ILI symptoms had a higher magnitude of IFNγ producing CD8 + T cells, compared to those reporting symptoms, as measured in ELISpot assays after stimulation with the pdm09 virus or peptides representing conserved CD8 + T cell epitopes (uCD8i). These antigen-specific CD8 + T cells are of particular interest due to their ability to provide cross-protective immunity against a range of influenza viruses [20,21,30,31], and may provide the basis for universal influenza vaccine development [16,32]. The inverse correlation observed between reported symptoms and frequency of IFNγ-secreting T cells indicates a putative protective effect of this cell population against symptomatic pandemic influenza illness during pregnancy. ...
Maternal influenza infection during pregnancy is associated with increased risk of morbidity and mortality. However, the link between the anti-influenza immune responses and health-related risks during infection is not well understood. We have analyzed memory T and NK cell mediated immunity (CMI) responses in pandemic influenza A(H1N1)pdm09 (pdm09) virus infected non-vaccinated pregnant women participating in the Norwegian Influenza Pregnancy Cohort (NorFlu). The cohort includes information on immunization, self-reported health and disease status, and biological samples (plasma and PBMC). Infected cases (N = 75) were defined by having a serum hemagglutination inhibition (HI) titer > = 20 to influenza pdm09 virus at the time of delivery, while controls (N = 75) were randomly selected among non-infected pregnant women (HI titer <10). In ELISpot assays cases had higher frequencies of IFNγ⁺ CD8⁺ T cells responding to pdm09 virus or conserved CD8 T cell-restricted influenza A virus epitopes, compared to controls. Within this T cell population, frequencies of CD95⁺ late effector (CD45RA⁺CCR7⁻) and naive (CD45RA⁺CCR7⁺) CD8⁺ memory T cells correlated inversely with self-reported influenza illness (ILI) symptoms. ILI symptoms in infected women were also associated with lower numbers of poly-functional (IFNγ⁺TNFα⁺, IL2⁺IFNγ⁺, IL2⁺IFNγ⁺TNFα⁺) CD4⁺ T cells and increased frequencies of IFNγ⁺CD3⁻CD7⁺ NK cells compared to asymptomatic cases, or controls, after stimulation with the pdm09 virus. Taken together, virus specific and functionally distinct T and NK cell populations may serve as cellular immune correlates of clinical outcomes of pandemic influenza disease in pregnant women. Our results may provide information important for future universal influenza vaccine design.
... These ecological observations suggest that infection may confer limited cross-protection from other subtypes. However, in addition to 2 studies during the 1957 pandemic that reported how prior infection with seasonal influenza subtypes correlated with protection against the pandemic influenza A/ Singapore/1/57(H2N2) virus [7,8], the strength of homo-or heterotypic cross-protective effects remains poorly characterized. Also, past influenza pandemics have been associated with an "age shift" in mortality patterns relative to seasonal influenza [9,10]. ...
Background:
After 2009, pandemic influenza A(H1N1) [A(H1N1)pdm09] cocirculated with A(H3N2) and B in Singapore.
Methods:
A cohort of 760 participants contributed demographic data and up to 4 blood samples each from October 2009 to September 2010. We compared epidemiology of the 3 subtypes and investigated evidence for heterotypic immunity through multivariable logistic regression using a generalized estimating equation. To examine age-related differences in severity between subtypes, we used LOESS (locally weighted smoothing) plots of hospitalization to infection ratios and explored birth cohort effects referencing the pandemic years (1957; 1968).
Results:
Having more household members aged 5-19 years and frequent public transport use increased risk of infection, while preexisting antibodies against the same subtype (odds ratio [OR], 0.61; P = .002) and previous influenza infection against heterotypic infections (OR, 0.32; P = .045) were protective. A(H1N1)pdm09 severity peaked in those born around 1957, while A(H3N2) severity was least in the youngest individuals and increased until it surpassed A(H1N1)pdm09 in those born in 1952 or earlier. Further analysis showed that severity of A(H1N1)pdm09 was less than that for A(H3N2) in those born in 1956 or earlier (P = .021) and vice versa for those born in 1968 or later (P < .001), with no difference in those born between 1957 and 1967 (P = .632).
Conclusions:
Our findings suggest that childhood exposures had long-term impact on immune responses consistent with the theory of antigenic sin. This, plus observations on short-term cross-protection, have implications for vaccination and influenza epidemic and pandemic mitigation strategies.
Influenza viruses continually evolve new antigenic variants, through mutations in epitopes of their major surface proteins, hemagglutinin (HA) and neuraminidase (NA). Antigenic drift potentiates the reinfection of previously infected individuals, but the contribution of this process to variability in annual epidemics is not well understood. Here we link influenza A(H3N2) virus evolution to regional epidemic dynamics in the United States during 1997—2019. We integrate phenotypic measures of HA antigenic drift and sequence-based measures of HA and NA fitness to infer antigenic and genetic distances between viruses circulating in successive seasons. We estimate the magnitude, severity, timing, transmission rate, age-specific patterns, and subtype dominance of each regional outbreak and find that genetic distance based on broad sets of epitope sites is the strongest evolutionary predictor of A(H3N2) virus epidemiology. Increased HA and NA epitope distance between seasons correlates with larger, more intense epidemics, higher transmission, greater A(H3N2) subtype dominance, and a greater proportion of cases in adults relative to children, consistent with increased population susceptibility. Based on random forest models, A(H1N1) incidence impacts A(H3N2) epidemics to a greater extent than viral evolution, suggesting that subtype interference is a major driver of influenza A virus infection dynamics, presumably via heterosubtypic cross-immunity.
Influenza viruses continually evolve new antigenic variants, through mutations in epitopes of their major surface proteins, hemagglutinin (HA) and neuraminidase (NA). Antigenic drift potentiates the reinfection of previously infected individuals, but the contribution of this process to variability in annual epidemics is not well understood. Here we link influenza A(H3N2) virus evolution to regional epidemic dynamics in the United States during 1997—2019. We integrate phenotypic measures of HA antigenic drift and sequence-based measures of HA and NA fitness to infer antigenic and genetic distances between viruses circulating in successive seasons. We estimate the magnitude, severity, timing, transmission rate, age-specific patterns, and subtype dominance of each regional outbreak and find that genetic distance based on broad sets of epitope sites is the strongest evolutionary predictor of A(H3N2) virus epidemiology. Increased HA and NA epitope distance between seasons correlates with larger, more intense epidemics, higher transmission, greater A(H3N2) subtype dominance, and a greater proportion of cases in adults relative to children, consistent with increased population susceptibility. Based on random forest models, A(H1N1) incidence impacts A(H3N2) epidemics to a greater extent than viral evolution, suggesting that subtype interference is a major driver of influenza A virus infection dynamics, presumably via heterosubtypic cross-immunity.
Impact statement: Antigenic drift in influenza’s major surface proteins – hemagglutinin and neuraminidase – contributes to variability in epidemic magnitude across seasons but is less influential than subtype interference in shaping annual outbreaks.
Influenza A viruses (IAV) exist as distinct serological subtypes, with limited antibody cross reactivity compared to T cell responses, leading to universal vaccines that elicit robust T cell responses entering clinical trials to combat pandemic and zoonotic outbreaks. Previously we have extensively characterized the viral vectored universal vaccine, Wyeth/IL‐15/5flu, a group 1 HA, H5N1 based vaccine using a vaccinia backbone with IL‐15. The vaccine elicits robust T cell responses to provide heterosubtypic protection from lethal infection; however, we have also observed short‐term morbidity of vaccinated mice with a disparity between the effects of sublethal infection with group 1 and 2 IAV strains. At day 3 of H3N2 (group 2 IAV) infection, there was a heavily skewed Th1 response in vaccinated infected mice with overproduction of cytokines and reduced chemokines, whilst H1N1 (group 1 IAV) infection had increased innate cellular responses. These findings suggest that increased and early immune activation by T cell activating vaccines may induce mild immunopathology when there is a mismatch between non‐neutralizing antibody and cross‐reactive memory T cell responses leading to exuberant cytokine production. Therefore, to avoid overstimulating proinflammatory immune responses upon infection, universal influenza vaccines that elicit strong T cell immunity will need a robust cross‐reactive antibody response.
We report in-concert dynamics of 18 key immune parameters, related to clinical, genetic and virological factors, in patients hospitalized with influenza across different severity levels. Influenza disease was associated with correlated increases in IL6/IL-8/MIP-1; cytokines and lower antibody responses. Robust activation of circulating T follicular helper cells (cTfhs) correlated with peak antibody-secreting cells (ASC) and influenza heamaglutinin-specific memory B-cell numbers, which phenotypically differed from vaccination-induced B-cell responses. Influenza-specific CD8+/CD4+ T-cells increased early in disease and remained activated during patient recovery. Here, we describe the broadest to-date immune cellular networks underlying recovery from influenza infection, highly relevant to other infectious diseases.
Immunological memory and tolerance represent major achievements and advantages of adaptive immunity. Organisms bearing adaptive immunity display prominent competitive advantages in the fight against infections. Memory immune cells are preserved for decades and are able to repel a second attack of an infectious agent. However, studies performed in the XXI century have shown that even unrelated pathogens may be quickly and effectively destroyed by memory cells. This type of response is called heterologous so that heterologous immune response is mainly typical to viral infections and other intracellular infections, where T-cells play a lead role in protection. This review will discuss various mechanisms involved in implementing T-cell cross-reactivity, describe molecular prerequisites for heterologous T-cell responses. Experimental evidence of memory T-cell potential to heterologous immune response in mouse models and in human infections are also discussed. Heterologous immune response is an important immune arm in adults and the elderly when the yield of naive cells to the periphery declines due to thymus involution. Along with obvious advantages, heterologous immune response leads to imbalanced memory T-cell repertoire, replacement of immunodominant epitopes with minor ones allowing viruses to evade immune response that results in virus persistence, or, conversely, fulminant infection course. Another threat of heterologous immune response due to switch in dominant repertoire of recognizable epitopes is presented by random self-epitope recognition, which can lead to development of autoimmune pathology. Heterologous immunity can also disrupt drug-induced tolerance in organ and tissue transplants and lead to graft rejection. Heterologous immune response should be taken into consideration while developing and using new vaccines, especially in adults and the elderly.
Seasonal influenza has a significant health care and economic impact and pandemic influenza is believed to have the potential to result in a global catastrophe. Regardless of developments with antivirals, vaccination remains the most effective option for limiting the impact of both seasonal and pandemic influenza.
Individuals are exposed to influenza viruses throughout their lifetime. Accumulating evidence shows the first viruses an individual is exposed to leaves an imprint on the antibody response induced by subsequent drifted and novel influenza viral exposures. Imprinted humoral immunity against influenza viruses relies on biased immune memory to influenza viruses for which memory B cell responses were initially generated against. Imprinting allows for antibodies to adapt to drifted influenza viruses while maintaining binding potential for the first influenza viruses an individual is exposed to. However, imprinting can increase susceptibility to non-imprinted influenza viruses and mismatched influenza viruses. This review highlights the role of imprinting on the regulation of antibody responses induced by influenza viruses and explores potential vaccine strategies to harness imprinted antibody responses to increase protection against influenza.
Severe influenza A virus (IAV) infection is associated with immune dysfunction. Here, we show circulating CD8+T-cell profiles from patients hospitalized with avian H7N9, seasonal IAV, and influenza vaccinees. Patient survival reflects an early, transient prevalence of highly activated CD38+HLA-DR+PD-1+CD8+T cells, whereas the prolonged persistence of this set is found in ultimately fatal cases. Single-cell T cell receptor (TCR)-αβ analyses of activated CD38+HLA-DR+CD8+T cells show similar TCRαβ diversity but differential clonal expansion kinetics in surviving and fatal H7N9 patients. Delayed clonal expansion associated with an early dichotomy at a transcriptome level (as detected by single-cell RNAseq) is found in CD38+HLA-DR+CD8+T cells from patients who succumbed to the disease, suggesting a divergent differentiation pathway of CD38+HLA-DR+CD8+T cells from the outset during fatal disease. Our study proposes that effective expansion of cross-reactive influenza-specific TCRαβ clonotypes with appropriate transcriptome signatures is needed for early protection against severe influenza disease.
Fifty years after the discovery of Epstein-Barr virus (EBV), it remains unclear how primary infection with this virus leads to massive CD8 T-cell expansion and acute infectious mononucleosis (AIM) in young adults. AIM can vary greatly in severity, from a mild transient influenza-like illness to a prolonged severe syndrome. We questioned whether expansion of a unique HLA-A2.01-restricted, cross-reactive CD8 T-cell response between influenza virus A-M158 (IAV-M1) and EBV BMLF1280 (EBV-BM) could modulate the immune response to EBV and play a role in determining the severity of AIM in 32 college students. Only ex vivo total IAV-M1 and IAV-M1+EBV-BM cross-reactive tetramer⁺ frequencies directly correlated with AIM severity and were predictive of severe disease. Expansion of specific cross-reactive memory IAV-M1 T-cell receptor (TCR) Vβ repertoires correlated with levels of disease severity. There were unique profiles of qualitatively different functional responses in the cross-reactive and EBV-specific CD8 T-cell responses in each of the three groups studied, severe-AIM patients, mild-AIM patients, and seropositive persistently EBV-infected healthy donors, that may result from differences in TCR repertoire use. IAV-M1 tetramer⁺ cells were functionally cross-reactive in short-term cultures, were associated with the highest disease severity in AIM, and displayed enhanced production of gamma interferon, a cytokine that greatly amplifies immune responses, thus frequently contributing to induction of immunopathology. Altogether, these data link heterologous immunity via CD8 T-cell cross-reactivity to CD8 T-cell repertoire selection, function, and resultant disease severity in a common and important human infection. In particular, it highlights for the first time a direct link between the TCR repertoire with pathogenesis and the diversity of outcomes upon pathogen encounter.
Heterotypic immunity to influenza virus in ferrets operated against heterotypic influenza viruses but not heterologous viruses. Contrary to prior reports, the protection conferred lasted for at least 18 months. This type of immunity limited virus shedding but did not prevent infection. These results suggest that this phenomenon could play a role in determining the severity of infections caused by type A influenza viruses in humans.
Resistance to infection with an influenza A virus conferred by previous infection with an influenza A virus belonging to another subtype is called heterosubtypic immunity. Heterosubtypic immunity is demonstrable in laboratory animals but is believed to be weak in humans. The present study examined whether heterosubtypic immunity from previous influenza virus infection induced resistance to infection with an attenuated influenza A vaccine virus. Two groups of vaccinees consisting of young infants and children who received either influenza A H1N1 or H3N2 attenuated virus were studied. Influenza A H3N2 virus vaccine recipients were classified by their preexisting H1N1 heterosubtypic antibody level induced by prior infection with wild-type virus, and the H1N1 vaccinees were classified by their history of infection with H3N2 vaccine virus. For both groups of vaccinees, the rates of seroconversion and virus shedding and the level of vaccine virus replication were compared in subjects with and without heterosubtypic immunity. In 48 influenza A H3N2 virus and 39 H1N1 virus vaccinees, heterosubtypic immunity had no demonstrable effect on infectivity, immunogenicity, or replication of attenuated vaccine virus. These observations confirm the weak nature of heterosubtypic immunity in humans and suggest that it will not limit the utility of live attenuated influenza A viruses in young infants and children.
DNA vaccination is an effective means of eliciting both humoral and cellular immunity, including cytotoxic T lymphocytes (CTL). Using an influenza virus model, we previously demonstrated that injection of DNA encoding influenza virus nucleoprotein (NP) induced major histocompatibility complex class I-restricted CTL and cross-strain protection from lethal virus challenge in mice (J. B. Ulmer et al., Science 259:1745-1749, 1993). In the present study, we have characterized in more detail the cellular immune responses induced by NP DNA, which included robust lymphoproliferation and Th1-type cytokine secretion (high levels of gamma interferon and interleukin-2 [IL-2], with little IL-4 or IL-10) in response to antigen-specific restimulation of splenocytes in vitro. These responses were mediated by CD4+ T cells, as shown by in vitro depletion of T-cell subsets. Taken together, these results indicate that immunization with NP DNA primes both cytolytic CD8+ T cells and cytokine-secreting CD4+ T cells. Further, we demonstrate by adoptive transfer and in vivo depletion of T-cell subsets that both of these types of T cells act as effectors in protective immunity against influenza virus challenge conferred by NP DNA.
Recently, an avian influenza A virus (A/Hong Kong/156/97, H5N1) was isolated from a young child who had a fatal influenza illness. All eight RNA segments were of avian origin. The H5 hemagglutinin is not recognized by neutralizing Abs present in humans as a result of infection with the human H1, H2, or H3 subtypes of influenza A viruses. Subsequently, five other deaths and several more human infections in Hong Kong were associated with this avian-derived virus. We investigated whether influenza A-specific human CD8+ and CD4+ T lymphocytes would recognize epitopes on influenza A virus strains derived from swine or avian species, including the 1997 H5N1 Hong Kong virus strains. Our results demonstrate that adults living in an urban area of the U.S. possess influenza A cross-serotype reactive CD8+ and CD4+ CTL that recognize multiple epitopes on influenza A viruses of other species. Bulk culture cytotoxicity was demonstrated against avian and human influenza A viruses. Enzyme-linked immunospot assays detected precursor CTL specific for both human CTL epitopes and the corresponding A/HK/97 viral sequences. We hypothesize that these cross-reactive CTL might provide partial protection to humans against novel influenza A virus strains introduced into humans from other species.
A growing proportion of young children in the United States participate in day care, and these children are considered to be at high risk for influenza infection. Whether vaccinating day care children reduces household transmission of influenza is not known.
To evaluate the effect of vaccinating day care children on reducing influenza-related morbidity among their household contacts.
Single-blind, randomized controlled trial conducted during the 1996-1997 influenza season.
Ten day care centers for children of US Navy personnel in San Diego, Calif.
A total of 149 day care attendees (aged 24-60 months) and their families were randomized; 127 children and their 328 household contacts received 2 vaccine doses and were included in the analysis.
Inactivated influenza vaccine was administered to 60 children with 162 household contacts, and hepatitis A vaccine as a control was administered to 67 age-matched children with 166 household contacts.
Information regarding febrile respiratory illnesses and related morbidity for household contacts of influenza-vaccinated vs control children (subgrouped by influenza-vaccinated and unvaccinated contacts), obtained by telephone interviews with parents every 2 weeks from November 1996 through April 1997.
Influenza-unvaccinated household contacts (n = 120) of influenza-vaccinated day care children had 42% fewer febrile respiratory illnesses (P =.04) compared with unvaccinated household contacts of control children. Among school-aged household contacts (aged 5-17 years), there was an 80% reduction among contacts of vaccinated children (n = 28) vs contacts of unvaccinated children (n = 31) in febrile respiratory illnesses (P =.01), as well as reductions of more than 70% in school days missed (P =.02), reported earaches (P =.02), physician visits (P =.007), physician-prescribed antibiotics (P =.02), and adults who missed work to take care of ill children (P =.04).
These results indicate that vaccinating day care children against influenza helps reduce influenza-related morbidity among their household contacts, particularly among school-aged contacts. Future studies should be conducted in civilian populations to assess the full effect of vaccinating day care children against influenza. JAMA. 2000;284:1677-1682.
In 1997, avian H5N1 influenza virus transmitted from chickens to humans resulted in 18 confirmed infections. Despite harboring lethal H5N1 influenza viruses, most chickens in the Hong Kong poultry markets showed no disease signs. At this time, H9N2 influenza viruses were cocirculating in the markets. We investigated the role of H9N2 influenza viruses in protecting chickens from lethal H5N1 influenza virus infections. Sera from chickens infected with an H9N2 influenza virus did not cross-react with an H5N1 influenza virus in neutralization or hemagglutination inhibition assays. Most chickens primed with an H9N2 influenza virus 3 to 70 days earlier survived the lethal challenge of an H5N1 influenza virus, but infected birds shed H5N1 influenza virus in their feces. Adoptive transfer of T lymphocytes or CD8(+) T cells from inbred chickens (B(2)/B(2)) infected with an H9N2 influenza virus to naive inbred chickens (B(2)/B(2)) protected them from lethal H5N1 influenza virus. In vitro cytotoxicity assays showed that T lymphocytes or CD8(+) T cells from chickens infected with an H9N2 influenza virus recognized target cells infected with either an H5N1 or H9N2 influenza virus in a dose-dependent manner. Our findings indicate that cross-reactive cellular immunity induced by H9N2 influenza viruses protected chickens from lethal infection with H5N1 influenza viruses in the Hong Kong markets in 1997 but permitted virus shedding in the feces. Our findings are the first to suggest that cross-reactive cellular immunity can change the outcome of avian influenza virus infection in birds in live markets and create a situation for the perpetuation of H5N1 influenza viruses.
Influenza vaccines that induce greater cross-reactive or heterosubtypic immunity (Het-I) may overcome limitations in vaccine efficacy imposed by the antigenic variability of influenza A viruses. We have compared mucosal versus traditional parenteral administration of inactivated influenza vaccine for the ability to induce Het-I in BALB/c mice and evaluated a modified Escherichia coli heat-labile enterotoxin adjuvant, LT(R192G), for augmentation of Het-I. Mice that received three intranasal (i.n.) immunizations of H3N2 vaccine in the presence of LT(R192G) were completely protected against lethal challenge with a highly pathogenic human H5N1 virus and had nasal and lung viral titers that were at least 2,500-fold lower than those of control mice receiving LT(R192G) alone. In contrast, mice that received three vaccinations of H3N2 vaccine subcutaneously in the presence or absence of LT(R192G) or incomplete Freund's adjuvant were not protected against lethal challenge and had no significant reductions in tissue virus titers observed on day 5 post-H5N1 virus challenge. Mice that were i.n. administered H3N2 vaccine alone, without LT(R192G), displayed partial protection against heterosubtypic challenge. The immune mediators of Het-I were investigated. The functional role of B and CD8+ T cells in Het-I were evaluated by using gene-targeted B-cell (IgH-6(-/-))- or beta2-microglobulin (beta2m(-/-))-deficient mice, respectively. beta2m(-/-) but not IgH-6(-/-) vaccinated mice were protected by Het-I and survived a lethal infection with H5N1, suggesting that B cells, but not CD8+ T cells, were vital for protection of mice against heterosubtypic challenge. Nevertheless, CD8+ T cells contributed to viral clearance in the lungs and brain tissues of heterotypically immune mice. Mucosal but not parenteral vaccination induced subtype cross-reactive lung immunoglobulin G (IgG), IgA, and serum IgG anti-hemagglutinin antibodies, suggesting the presence of a common cross-reactive epitope in the hemagglutinins of H3 and H5. These results suggest a strategy of mucosal vaccination that stimulates cross-protection against multiple influenza virus subtypes, including viruses with pandemic potential.
To examine the molecular epidemiology of influenza virus transmission, the nucleotide sequences of the HA1 domain of the hemagglutinin
(HA) gene of 57 influenza A and 24 influenza B viruses recovered in a single season were analyzed. No nucleotide sequence
differences were found among the 10 viruses that were recovered twice from the same patient. The nucleotide sequences of influenza
A viruses were identical within each family but varied among the 14 families included in the study. The sequences of influenza
A viruses recovered from 18 residents of the same community showed that 83% of the viruses differed from the others by at
least 1 nucleotide residue. These findings indicate that most cases of influenza in households in which 1 family member has
been infected are the result of secondary transmission from the index patient and not of acquisition from other community
sources. Substantial genetic conservation during virus transmission within households is indicated
The level of heterosubtypic immunity (Het-I) and the immune mechanisms stimulated by a heterosubtypic influenza virus infection were investigated in pigs. Pigs are natural hosts for influenza virus and, like humans, they host both subtypes H1N1 and H3N2. Marked Het-I was observed when pigs were infected with H1N1 and subsequently challenged with H3N2. After challenge with H3N2, pigs infected earlier with H1N1 did not develop fever and showed reduced virus excretion compared with non-immune control pigs. In addition, virus transmission to unchallenged group-mates could be shown by virus isolation in the non-immune control group but not in the group infected previously with H1N1. Pigs infected previously with homologous H3N2 virus were protected completely. After challenge with H3N2, pigs infected previously with H1N1 showed a considerable increase in serum IgG titre to the conserved extracellular domain of M2 but not to the conserved nucleoprotein. These results suggest that antibodies against external conserved epitopes can have an important role in broad-spectrum immunity. After primary infection with both H1N1 and H3N2, a long-lived increase was observed in the percentage of CD8(+) T cells in the lungs and in the lymphoproliferation response in the blood. Upon challenge with H3N2, pigs infected previously with H1N1 again showed an increase in the percentage of CD8(+) T cells in the lungs, whereas pigs infected previously with H3N2 did not, suggesting that CD84(+) T cells also have a role in Het-I. To confer broad-spectrum immunity, future vaccines should induce antibodies and CD8(+)T cells against conserved antigens.
Context A growing proportion of young children in the United States participate
in day care, and these children are considered to be at high risk for influenza
infection. Whether vaccinating day care children reduces household transmission
of influenza is not known.Objective To evaluate the effect of vaccinating day care children on reducing
influenza-related morbidity among their household contacts.Design Single-blind, randomized controlled trial conducted during the 1996-1997
influenza season.Setting Ten day care centers for children of US Navy personnel in San Diego,
Calif.Participants A total of 149 day care attendees (aged 24-60 months) and their families
were randomized; 127 children and their 328 household contacts received 2
vaccine doses and were included in the analysis.Interventions Inactivated influenza vaccine was administered to 60 children with 162
household contacts, and hepatitis A vaccine as a control was administered
to 67 age-matched children with 166 household contacts.Main Outcome Measures Information regarding febrile respiratory illnesses and related morbidity
for household contacts of influenza-vaccinated vs control children (subgrouped
by influenza-vaccinated and unvaccinated contacts), obtained by telephone
interviews with parents every 2 weeks from November 1996 through April 1997.Results Influenza-unvaccinated household contacts (n = 120) of influenza-vaccinated
day care children had 42% fewer febrile respiratory illnesses (P = .04) compared with unvaccinated household contacts of control children.
Among school-aged household contacts (aged 5-17 years), there was an 80% reduction
among contacts of vaccinated children (n = 28) vs contacts of unvaccinated
children (n = 31) in febrile respiratory illnesses (P
= .01), as well as reductions of more than 70% in school days missed (P = .02), reported earaches (P
= .02), physician visits (P = .007), physician-prescribed
antibiotics (P = .02), and adults who missed work
to take care of ill children (P = .04).Conclusions These results indicate that vaccinating day care children against influenza
helps reduce influenza-related morbidity among their household contacts, particularly
among school-aged contacts. Future studies should be conducted in civilian
populations to assess the full effect of vaccinating day care children against
influenza.
A total of 663 pupils at four schools were studied serologically and clinically during a period of large sequential and/or
mixed epidemics of infection with two subtypes of influenza A virus, H3N2 and H1N1. Of 91 middle-school pupils infected with
H3N2 virus shortly before and 82 pupils not previously infected with this subtype, 59070 and 91% became infected with H1N1
virus, respectively; this difference was significant. Similar results were obtained at the two primary schools studied. At
a high school where epidemics due to the H3N2 and H1N1 subtypes occurred concurrently, the rate of infection of individual
pupils with both viruses (2%) was significantly lower than those at the other three schools (21%, 23%, and 31%, respectively),
where an epidemic caused by the H3N2 subtype appeared first and was then partially overlapped and succeeded by an epidemic
caused by the H1N1 subtype. These findings suggest the existence of cross-subtype protection in humans during sequential and/or
concurrent epidemics caused by two viral subtypes.
Masurel, Nic (Dept. of Virology, Medical Faculty Rotterdam, P.O. Box 1738, Rotterdam, The Netherlands), and William M. Marine. Recycling of Asian and Hong Kong influenza A virus hemagglutinins in man. Am J Epidemiol 97: 44-49, 1973.-Pre-Asian/57 and post-Hong Kong/ 68 epidemic sera were studied for antibodies to A/Japan/305/57 (H2N2), A/Hong Kong/1/68 (H3N2), and A/Equine/63 (Heq2Neq2) viruses by the hemagglutination-inhibition test. The relationship of antibodies in pre-Asian/57 sera further established the hypothesis that a Hong Kong/ 68-like virus stimulated antibody cross-reacting asymmetrically with Hong Kong/68 and Equine/63 hemagglutinins. The lack of a predictable quantitative and qualitative relationship of Asian/57 and Hong Kong/68 antibodies in the pre-Asian/57 sera, together with the different timing of increase in prevalence to these two hemagglutinins, lead to a unified hypothesis for recycling of Asian/57-like and Hong Kong/68-like viruses. The positive relationship between Asian/57 and Hong Kong/68 antibodies in the pre-Asian/57 and post-Hong Kong/68 collection of sera is explained by the anamnestic stimulation of Asian/57 antibody. A hemagglutinin-mediated anamnestic response in Asian/57 antibody by Hong Kong/68 vaccine was confirmed in a group of young adults, using hemagglutinin-specific recomhinants. Although the data do not permit the exact timing of this recycling, we can be quite certain that influenza viruses with Asian/57-like and Hong Kong/68-like hemagglutinins occurred in the same sequence at the end of the 19th century as was seen in 1957 and 1968. The implications of this conclusion include the prediction that a Swine-like influenza A virus may recur in man by 1985-1990.
A recombinant baculovirus expressing the M2 protein from influenza A/Ann Arbor/6/60 (H2N2) virus (AA60 virus) was constructed. The expressed M2 protein was recognized by a monoclonal antibody specific for the M2 protein and comigrated with the M2 protein from cells infected with AA60 virus on SDS-polyacrylamide gels. Immunofluorescence studies indicated that the expressed M2 protein was present on the surface of Spodoptera frugiperda (Sf9) cells infected with the recombinant baculovirus. Immunoassays using the expressed M2 protein were able to detect antibodies to the M2 protein in serum samples from humans and ferrets infected with influenza A viruses.
Class I restricted cytotoxic T-lymphocyte (CTL) responses are thought to be focused against few immunodominant epitopes. In humans, an often quoted example of such narrow focus is the influenza A (FLU) matrix 58-66 specific memory CTL activity, detectable in HLA-A2 individuals as a result of natural infection. Herein, we analyzed the repertoire of memory, FLU-specific CTLs in A2 and A11 positive individuals. Eighteen A2.1 binding peptides, derived from the FLU-Puerto Rico/8/34 (PR8) isolate, elicited CTL activity in A2. 1/Kb transgenic mice upon direct immunization. These peptides were also tested for their capacity to recall memory CTL responses from peripheral blood mononuclear cells (PBMC) of human A2.1 donors. Besides the known dominant M1.58 peptide, 5 new epitopes (PA.46, PA. 225, PB1.413, NA.75 and M1.59) were identified. Similarly, eleven, A11-binding, FLU-PR8 peptides, which were immunogenic in HLA-A11/Kb transgenic mice, were assayed for induction of recall CTL responses using peripheral blood lymphocytes from a cohort of A11-positive donors. Eight different peptides (NP.188, NP.342, HA.63(,) HA.149, HA.450, M1.13, M1.178, and M2.70) induced memory CTL activity. Several of these peptides were found to be highly conserved amongst different FLU isolates, and also capable of binding multiple A2 and A11 supertype molecules. Finally, 37 HLA-B7 binding peptides were also identified. In conclusion, a previously unappreciated breadth of FLU-specific, memory CTL responses in humans was revealed. The relevance of these findings to the design of multiepitope vaccines is discussed.
Influenza virus is easily spread among the household contacts of an infected person, and prevention of influenza in household contacts can control spread of influenza in the community.
To investigate the efficacy of oseltamivir in preventing spread of influenza to household contacts of influenza-infected index cases (ICs).
Randomized, double-blind, placebo-controlled study conducted at 76 centers in North America and Europe during the winter of 1998-1999.
Three hundred seventy-seven ICs, 163 (43%) of whom had laboratory-confirmed influenza infection, and 955 household contacts (aged >/=12 years) of all ICs (415 contacts of influenza-positive ICs).
Household contacts were randomly assigned by household cluster to take 75 mg of oseltamivir (n = 493) or placebo (n = 462) once daily for 7 days within 48 hours of symptom onset in the IC. The ICs did not receive antiviral treatment.
Clinical influenza in contacts of influenza-positive ICs, confirmed in a laboratory by detection of virus shedding in nose and throat swabs or a 4-fold or greater increase in influenza-specific serum antibody titer between baseline and convalescent serum samples.
In contacts of an influenza-positive IC, the overall protective efficacy of oseltamivir against clinical influenza was 89% for individuals (95% confidence interval [CI], 67%-97%; P<.001) and 84% for households (95% CI, 49%-95%; P<.001). In contacts of all ICs, oseltamivir also significantly reduced incidence of clinical influenza, with 89% protective efficacy (95% CI, 71%-96%; P<.001). Viral shedding was inhibited in contacts taking oseltamivir, with 84% protective efficacy (95% CI, 57%-95%; P<.001). All virus isolates from oseltamivir recipients retained sensitivity to the active metabolite. Oseltamivir was well tolerated; gastrointestinal tract effects were reported with similar frequency in oseltamivir (9.3%) and placebo (7.2%) recipients.
In our sample, postexposure prophylaxis with oseltamivir, 75 mg once daily for 7 days, protected close contacts of influenza-infected persons against influenza illness, prevented outbreaks within households, and was well tolerated.
The level of heterosubtypic immunity (Het-I) and the immune mechanisms stimulated by a heterosubtypic influenza virus infection were investigated in pigs. Pigs are natural hosts for influenza virus and, like humans, they host both subtypes H1N1 and H3N2. Marked Het-I was observed when pigs were infected with H1N1 and subsequently challenged with H3N2. After challenge with H3N2, pigs infected earlier with H1N1 did not develop fever and showed reduced virus excretion compared with non-immune control pigs. In addition, virus transmission to unchallenged group-mates could be shown by virus isolation in the non-immune control group but not in the group infected previously with H1N1. Pigs infected previously with homologous H3N2 virus were protected completely. After challenge with H3N2, pigs infected previously with H1N1 showed a considerable increase in serum IgG titre to the conserved extracellular domain of M2 but not to the conserved nucleoprotein. These results suggest that antibodies against external conserved epitopes can have an important role in broad-spectrum immunity. After primary infection with both H1N1 and H3N2, a long-lived increase was observed in the percentage of CD8(+) T cells in the lungs and in the lymphoproliferation response in the blood. Upon challenge with H3N2, pigs infected previously with H1N1 again showed an increase in the percentage of CD8(+) T cells in the lungs, whereas pigs infected previously with H3N2 did not, suggesting that CD8(+) T cells also have a role in Het-I. To confer broad-spectrum immunity, future vaccines should induce antibodies and CD8(+) T cells against conserved antigens.
The author reports on the effect of a previous attack of influenza caused by virus A1 on susceptibility to virus A2 in the light of analyses made of the rate of sickness from influenza and acute catarrhs of the respiratory tract in a ball-bearing factory in the USSR in 1957. There were spring and summer rises in sickness and an autumn epidemic.In the summer rise, caused by A2 virus, the sickness rate for those who had been ill in the spring (with A1 influenza) was about half (4.7%) that for those who had not been affected in the spring (10.5%), but this was clearly an unstable and short-lived immunity as by the time of the autumn A2 epidemic the rate for those sick in the spring rose to 21.1% although this was still 1.6 times lower than that for those who had not been ill either in the spring or in the summer.Vaccination with a polyvalent vaccine (A, A1 and B strains) was partially effective in the summer epidemic, but slightly less so than seroprophylaxis with the same strains conducted in October. This also seems to indicate the working of the same phenomenon of partial immunity derived from an old variety of influenza virus of the same serological type as that causing an outbreak not long beforehand.
Schulman, Jerome L. (Cornell University Medical College, New York, N.Y.), and Edwin D. Kilbourne. Induction of partial specific heterotypic immunity in mice by a single infection with influenza A virus. J. Bacteriol.
89
170–174. 1965.—Mice infected 4 weeks previously with influenza A virus were found to be partially immune when challenged with influenza A2 virus. This partial immunity was demonstrated by reduced titers of pulmonary virus, decreased mortality, and less extensive lung lesions. A specific immunological basis for this protection was suggested by the absence of any protection in animals previously infected with influenza B virus when challenged with A2 virus, or in animals previously infected with influenza A virus when challenged with influenza B virus. Parenteral inoculation with inactivated influenza A virus did not induce partial immunity to A2 virus challenge. An accelerated rise of hemagglutinating-inhibiting antibody after A2 virus challenge was demonstrated in animals previously infected with influenza A virus.
Influenza has circulated among humans for centuries and kills more people than many newly emerging diseases. The present methods for control of influenza are not adequate, especially for dealing with a pandemic. In the face of a rapidly spreading outbreak, a race to isolate the virus and prepare a vaccine would probably not succeed in time to avoid great losses. Thus, additional anti-infection strategies are needed. Broad cross-protection against widely divergent influenza A subtypes is readily achieved in animals by several means of immunization. How does cross-protection work in animals, and can we apply what we have learned about it to induce broad cross-protection in humans?
Plan of study and certain general observations
I. Plan of study and certain general observations. Am J Hyg 1953; 58:
16-30.
- B R Murphy
- R G Webster
- Orthomyxoviruses
- B N Fields
- D M Knipe
- R M Chanock
Murphy BR, Webster RG. Orthomyxoviruses. In: Fields BN, Knipe DM,
Chanock RM, et al., eds. Fields virology. Vol. 1. 2nd ed. New York: Raven
Press, 1990:1091-152.