Broadly Reactive IgG Responses to Heterologous H5 Prime-Boost Influenza Vaccination Are Shaped by Antigenic Relatedness to Priming Strains.

Prime-boost vaccinations of humans with different H5 strains have generated broadly protective antibody levels. However, the effect of an individual's H5 exposure history on antibody responses to subsequent H5 vaccination is poorly understood. To investigate this, we analyzed the IgG responses to H5 influenza A/Indonesia/5/2005 (Ind05) virus vaccination in three cohorts: (i) a doubly primed group that had received two H5 virus vaccinations, namely, against influenza A/Vietnam/203/2004 (Vie04) virus 5 years prior and A/Hong Kong/156/1997 (HK97) 11 years prior to the Ind05 vaccination; (ii) a singly primed group that had received a vaccination against Vie04 virus 5 years prior to the Ind05 vaccination; and (iii) an H5-naive group that received two doses of the Ind05 vaccine 28 days apart. Hemagglutinin (HA)-reactive IgG levels were estimated by a multiplex assay against an HA panel that included 21 H5 strains and 9 other strains representing the H1, H3, H7, and H9 subtypes. Relative HA antibody landscapes were generated to quantitatively analyze the magnitude and breadth of antibody binding after vaccination. We found that short-interval priming and boosting with the Ind05 vaccine in the naive group generated a low anti-H5 response. Both primed groups generated robust antibody responses reactive to a broad range of H5 strains after receiving a booster injection of Ind05 vaccine; IgG antibody levels persisted longer in subjects who had been doubly primed years ago. Notably, the IgG responses were strongest against the first priming H5 strain, which reflects influenza virus immune imprinting. Finally, the broad anti-H5 IgG response was stronger against strains having a small antigenic distance from the initial priming strain. IMPORTANCE The antigenic shift and draft of hemagglutinin (HA) in influenza viruses is accepted as one of the major reasons for immune evasion. The analysis of B cell immune responses to influenza infection and vaccination is complicated by the impact of exposure history and antibody cross-reactions between antigenically similar influenza strains. To assist in such analyses, the influenza "antibody landscape" method has been used to analyze and visualize the relationship of antibody-mediated immunity to antigenic distances between influenza strains. In this study, we describe a "relative antibody landscape" method that calculates the antigenic distance between the vaccine influenza strain and other H5 strains and uses this relative antigenic distance to plot the anti-H5 IgG levels postvaccination. This new method quantitatively estimates and visualizes the correlation between the humoral response to a particular influenza strain and the antigenic distance from other strains. Our findings demonstrate the effect of a subject's H5 exposure history on H5 vaccine responses quantified by the relative antibody landscape method.

Social networks based on frequency of roost cohabitation do not reflect association rates of Myotis lucifugus within their roosts.

Bats are a group of mammals well known for forming dynamic social groups. Studies of bat social structures are often based upon the frequency at which bats occupy the same roosts because observing bats directly is not always possible. However, it is not always clear how closely bats occupying the same roost associate with each other, obscuring whether associations result from social relationships or factors such as shared preferences for roosts. Our goal was to determine if bats cohabitating buildings were also found together inside roosts by using anti-collision technology for PIT tags, which enables simultaneous detection of multiple tags. We PIT-tagged 293 female little brown myotis (Myotis lucifugus) and installed antennas within two buildings used as maternity roosts in Yellowstone National Park. Antennas were positioned at roost entryways to generate cohabitation networks and along regions of attic ceilings in each building to generate intraroost networks based on proximity of bats to each other. We found that intraroost and cohabitation networks of buildings were significantly correlated, with the same bats tending to be linked in both networks, but that bats cohabitating the same building often roosted apart, leading to differing assessments of social structure. Cohabitation rates implied that bats associate with a greater number of their roost-mates than was supported by observations within the roost. This caused social networks built upon roost cohabitation rates to be denser, smaller in diameter, and contain nodes with higher average degree centrality. These results show that roost cohabitation does not reflect preference for roost-mates in little brown myotis, as is often inferred from similar studies, and that social network analyses based on cohabitation may provide misleading results.

Adjuvanted recombinant hemagglutinin H7 vaccine to highly pathogenic influenza A(H7N9) elicits high and sustained antibody responses in healthy adults.

An unprecedented number of human infections with avian influenza A(H7N9) in the fifth epidemic wave during the winter of 2016-2017 in China and their antigenic divergence from the viruses that emerged in 2013 prompted development of updated vaccines for pandemic preparedness. We report on the findings of a clinical study in healthy adults designed to evaluate the safety and immunogenicity of three dose levels of recombinant influenza vaccine derived from highly pathogenic A/Guangdong/17SF003/2016 (H7N9) virus adjuvanted with AS03 or MF59 oil-in water emulsions. Most of the six study groups meet the FDA CBER-specified vaccine licensure criterion of 70% seroprotection rate (SPR) for hemagglutination inhibition antibodies to the homologous virus. A substantial proportion of subjects show high cross-reactivity to antigenically distinct heterologous A(H7N9) viruses from the first epidemic wave of 2013. These results provide critical information to develop a pandemic response strategy and support regulatory requirements for vaccination under Emergency Use Authorization.

Improving pandemic preparedness through better, faster influenza vaccines.

Introduction. Timely availability of effective influenza vaccine will be critical to mitigate the next influenza pandemic. The mission of Biomedical Advanced Research and Development Authority (BARDA) is to develop medical countermeasures against pandemics, including influenza and other health security threats.Areas covered. Despite considerable gains in pandemic vaccine preparedness since 2009, old and new challenges threaten the pandemic influenza response capabilities of the U.S. Government: insufficient U.S.-based vaccine production, two-dose vaccination regimen, logistically complex adjuvanted formulation, and sustained surge manufacturing capacity despite no commercial market for pandemic vaccines. Although the coronavirus disease 2019 (COVID-19) pandemic has re-exposed these gaps in preparedness and response, previous investments into flexible influenza vaccine technologies proved to be critical to accelerate COVID-19 vaccine development.Expert opinion. BARDA addresses these challenges by implementing a pandemic influenza vaccine strategy with two key goals: 1) accelerating vaccine development and production (faster) and 2) improving vaccine performance (better). This strategy involves an end-to-end approach, including increasing manufacturing and fill-finish capacity; improving release testing speed; and funding clinical trials to improve current vaccine utilization. As demonstrated by the COVID-19 response, continued investments into this pandemic influenza vaccine strategy will further enhance the ability to respond to future emerging pandemic pathogens.

Gaps in Serologic Immunity against Contemporary Swine-Origin Influenza A Viruses among Healthy Individuals in the United States.

Influenza A Viruses (IAV) in domestic swine (IAV-S) are associated with sporadic zoonotic transmission at the human-animal interface. Previous pandemic IAVs originated from animals, which emphasizes the importance of characterizing human immunity against the increasingly diverse IAV-S. We analyzed serum samples from healthy human donors (n = 153) using hemagglutination-inhibition (HAI) assay to assess existing serologic protection against a panel of contemporary IAV-S isolated from swine in the United States (n = 11). Age-specific seroprotection rates (SPR), which are the proportion of individuals with HAI ≥ 1:40, corresponded with lower or moderate pandemic risk classifications for the multiple IAV-S examined (one H1-δ1, one H1-δ2, three H3-IVA, one H3-IVB, one H3-IVF). Individuals born between 2004 and 2013 had SPRs of 0% for the five classified H3 subtype IAV-S, indicating youth may be particularly predisposed to infection with these viruses. Expansion of existing immunologic gaps over time could increase likelihood of future IAV-S spillover to humans and facilitate subsequent sustained human-to-human transmission resulting in disease outbreaks with pandemic potential.

Viewpoint of a WHO Advisory Group Tasked to Consider Establishing a Closely-monitored Challenge Model of Coronavirus Disease 2019 (COVID-19) in Healthy Volunteers.

WHO convened an Advisory Group (AG) to consider the feasibility, potential value, and limitations of establishing a closely-monitored challenge model of experimental severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019 (COVID-19) in healthy adult volunteers. The AG included experts in design, establishment, and performance of challenges. This report summarizes issues that render a COVID-19 model daunting to establish (the potential of SARS-CoV-2 to cause severe/fatal illness, its high transmissibility, and lack of a "rescue treatment" to prevent progression from mild/moderate to severe clinical illness) and it proffers prudent strategies for stepwise model development, challenge virus selection, guidelines for manufacturing challenge doses, and ways to contain SARS-CoV-2 and prevent transmission to household/community contacts. A COVID-19 model could demonstrate protection against virus shedding and/or illness induced by prior SARS-CoV-2 challenge or vaccination. A limitation of the model is that vaccine efficacy in experimentally challenged healthy young adults cannot per se be extrapolated to predict efficacy in elderly/high-risk adults.

Characterizing Emerging Canine H3 Influenza Viruses.

The continual emergence of novel influenza A strains from non-human hosts requires constant vigilance and the need for ongoing research to identify strains that may pose a human public health risk. Since 1999, canine H3 influenza A viruses (CIVs) have caused many thousands or millions of respiratory infections in dogs in the United States. While no human infections with CIVs have been reported to date, these viruses could pose a zoonotic risk. In these studies, the National Institutes of Allergy and Infectious Diseases (NIAID) Centers of Excellence for Influenza Research and Surveillance (CEIRS) network collaboratively demonstrated that CIVs replicated in some primary human cells and transmitted effectively in mammalian models. While people born after 1970 had little or no pre-existing humoral immunity against CIVs, the viruses were sensitive to existing antivirals and we identified a panel of H3 cross-reactive human monoclonal antibodies (hmAbs) that could have prophylactic and/or therapeutic value. Our data predict these CIVs posed a low risk to humans. Importantly, we showed that the CEIRS network could work together to provide basic research information important for characterizing emerging influenza viruses, although there were valuable lessons learned.

Evidence That Blunted CD4 T-Cell Responses Underlie Deficient Protective Antibody Responses to Influenza Vaccines in Repeatedly Vaccinated Human Subjects.

Despite the benefits of yearly influenza vaccination, accumulating evidence suggests that diminished vaccine efficacy may be related to repeated vaccination. Although studied at the level of B-cell responses, CD4 T-cell responses have not yet been examined. In this study, we analyze CD4 T-cell responses to influenza vaccination in subjects who differ in their vaccine history. We find a striking disparity in their responses, with previously vaccinated subjects exhibiting significantly blunted CD4 T-cell responses and diminished antibody responses. These results suggest that limiting CD4 T-cell help mteaserrlie the diminished or altered antibody responses in repeatedly vaccinated subjects.

Monoclonal Antibody Responses after Recombinant Hemagglutinin Vaccine versus Subunit Inactivated Influenza Virus Vaccine: a Comparative Study.

Vaccination is the best measure of protection against influenza virus infection. Vaccine-induced antibody responses target mainly the hemagglutinin (HA) surface glycoprotein, composed of the head and the stalk domains. Recently two novel vaccine platforms have been developed for seasonal influenza vaccination: a recombinant HA vaccine produced in insect cells (Flublok) and Flucelvax, prepared from virions produced in mammalian cells. In order to compare the fine specificity of the antibodies induced by these two novel vaccine platforms, we characterized 42 Flublok-induced monoclonal antibodies (MAbs) and 38 Flucelvax-induced MAbs for avidity, cross-reactivity, and any selectivity toward the head versus the stalk domain. These studies revealed that Flublok induced a greater proportion of MAbs targeting epitopes near the receptor-binding domain on HA head (hemagglutinin inhibition-positive MAbs) than Flucelvax, while the two vaccines induced similar low frequencies of stalk-reactive MAbs. Finally, mice immunized with Flublok and Flucelvax also induced similar frequencies of stalk-reactive antibody-secreting cells, showing that HA head immunodominance is independent of immune memory bias. Collectively, our results suggest that these vaccine formulations are similarly immunogenic but differ in the preferences of the elicited antibodies toward the receptor-binding domain on the HA head.IMPORTANCE There are ongoing efforts to increase the efficacy of influenza vaccines and to promote production strategies that can rapidly respond to newly emerging viruses. It is important to understand if current alternative seasonal vaccines, such as Flublok and Flucelvax, that use alternate production strategies can induce protective influenza-specific antibodies and to evaluate what type of epitopes are targeted by distinct vaccine formulations.

Continuous Readout versus Titer-Based Assays of Influenza Vaccine Trials: Sensitivity, Specificity, and False Discovery Rates.

The current gold standard for measuring antibody-based immunity to influenza viruses relies on the hemagglutinin inhibition assay (HAI), an 80-year-old technology, and the microneutralization assay (MN). Both assays use serial dilution to provide a discrete, ranked readout of 8-14 categorical titer values for each sample. In contrast to other methods of measuring vaccine antibody levels that produce a continuous readout (i.e., mPLEX-Flu and ELISA), titering methods introduce imprecision and increase false discovery rates (FDR). In this paper, we assess the degree of such statistical errors, first with simulation studies comparing continuous data with titer data in influenza vaccine study group comparison analyses and then by analyzing actual sample data from an influenza vaccine trial. Our results show the superiority of using continuous, rather than discrete, readout assays. Compared to continuous readout assays, titering assays have a lower statistical precision and a higher FDR. The results suggested that traditional titering assays could lead to increased Type-II errors in the comparison of different therapeutic arms of an influenza vaccine trial. These statistical issues are related to the mathematical nature of titer-based assays, which we examine in detail in the simulation studies. Continuous readout assays are free of this issue, and thus it is possible that comparisons of study groups could provide different results with these two methods as we have shown in our case study.

Improved Specificity and False Discovery Rates for Multiplex Analysis of Changes in Strain-Specific Anti-Influenza IgG.

We describe a statistical approach to compare absolute antibody concentrations, both within and across subjects, derived from a multidimensional measurement of IgG binding to the influenza surface receptor hemagglutinin (HA). This approach addresses a fundamental problem in the field of vaccine immunology: how to accurately compare the levels of antibodies against multiple influenza strains. The mPlex-Flu assay can simultaneously measure the concentration of IgG antibodies against up to 50 influenza strains with only ≤10 µl of serum. It yields mean fluorescence intensity (MFI) over a 4-log range with low inter- and intrasample variability. While comparison of IgG binding to a single HA between subjects is straightforward, variations in binding behavior across influenza strains, coupled with reagent variations, make quantifying and comparing binding between multiple HA subtypes within subjects challenging. In this paper, we first treat such HA variations as an independent antigen and calculate each subtype antibody concentration using its own standard curve, normalizing variations in HA binding. We applied this method to the analyses of data from an H5 influenza clinical vaccine study. The results demonstrated that there are differences in coefficient estimates and in results of "comparing groups" between those with versus those without consideration of subtype antibody variations. Then, we used simulation studies to show the importance of taking the subtype antibody variations into account in HA strain antibody data analysis. Using a common standard curve for all subtype antibodies resulted in both inflated type I error and lowered specificity when comparing different treatment groups. Our results suggest that using individual standard curves for each influenza HA strain, and independently calculating anti-HA IgG concentrations, allows for adjustment of influenza HA subtype variations in treatment group comparisons in clinical vaccine studies. This method facilitates the direct comparison of serum anti-HA IgG concentrations against different influenza HA subtypes for multiplex assays.

Influenza Virus Vaccination Elicits Poorly Adapted B Cell Responses in Elderly Individuals.

Influenza is a leading cause of death in the elderly, and the vaccine protects only a fraction of this population. A key aspect of antibody-mediated anti-influenza virus immunity is adaptation to antigenically distinct epitopes on emerging strains. We examined factors contributing to reduced influenza vaccine efficacy in the elderly and uncovered a dramatic reduction in the accumulation of de novo immunoglobulin gene somatic mutations upon vaccination. This reduction is associated with a significant decrease in the capacity of antibodies to target the viral glycoprotein, hemagglutinin (HA), and critical protective epitopes surrounding the HA receptor-binding domain. Immune escape by antigenic drift, in which viruses generate mutations in key antigenic epitopes, becomes highly exaggerated. Because of this reduced adaptability, most B cells activated in the elderly cohort target highly conserved but less potent epitopes. Given these findings, vaccines driving immunoglobulin gene somatic hypermutation should be a priority to protect elderly individuals.

Broad Hemagglutinin-Specific Memory B Cell Expansion by Seasonal Influenza Virus Infection Reflects Early-Life Imprinting and Adaptation to the Infecting Virus.

Memory B cells (MBCs) are key determinants of the B cell response to influenza virus infection and vaccination, but the effect of different forms of influenza antigen exposure on MBC populations has received little attention. We analyzed peripheral blood mononuclear cells and plasma collected following human H3N2 influenza infection to investigate the relationship between hemagglutinin-specific antibody production and changes in the size and character of hemagglutinin-reactive MBC populations. Infection produced increased concentrations of plasma IgG reactive to the H3 head of the infecting virus, to the conserved stalk, and to a broad chronological range of H3s consistent with original antigenic sin responses. H3-reactive IgG MBC expansion after infection included reactivity to head and stalk domains. Notably, expansion of H3 head-reactive MBC populations was particularly broad and reflected original antigenic sin patterns of IgG production. Findings also suggest that early-life H3N2 infection "imprints" for strong H3 stalk-specific MBC expansion. Despite the breadth of MBC expansion, the MBC response included an increase in affinity for the H3 head of the infecting virus. Overall, our findings indicate that H3-reactive MBC expansion following H3N2 infection is consistent with maintenance of response patterns established early in life, but nevertheless includes MBC adaptation to the infecting virus.IMPORTANCE Rapid and vigorous virus-specific antibody responses to influenza virus infection and vaccination result from activation of preexisting virus-specific memory B cells (MBCs). Understanding the effects of different forms of influenza virus exposure on MBC populations is therefore an important guide to the development of effective immunization strategies. We demonstrate that exposure to the influenza hemagglutinin via natural infection enhances broad protection through expansion of hemagglutinin-reactive MBC populations that recognize head and stalk regions of the molecule. Notably, we show that hemagglutinin-reactive MBC expansion reflects imprinting by early-life infection and that this might apply to stalk-reactive, as well as to head-reactive, MBCs. Our findings provide experimental support for the role of MBCs in maintaining imprinting effects and suggest a mechanism by which imprinting might confer heterosubtypic protection against avian influenza viruses. It will be important to compare our findings to the situation after influenza vaccination.

Differences in the influenza-specific CD4 T cell immunodominance hierarchy and functional potential between children and young adults.

Studies of the B cell repertoire suggest that early childhood influenza infections profoundly shape later reactivity by creating an "imprint" that impacts subsequent vaccine responses and may provide lasting protection against influenza strains within the same viral group. However, there is little known about how these early childhood influenza exposures shape CD4 T cell reactivity later in life. To investigate the effect of age on influenza-specific CD4 T cell specificity and functionality, reactivity in cohorts of 2 year old children and young adult subjects was compared. Intracellular cytokine staining was used to determine the viral antigen specificity and expression levels of various cytokines following stimulation of peripheral blood mononuclear cells with complete peptide pools representing the entire translated sequences of the pH1, H3, HA-B, NP, and M1 proteins. We found that the influenza protein-specific immunodominance pattern in children differs from that in young adults, with much lower reactivity to the NP internal virion protein in young children. Alterations in CD4 T cell functionality were also noted, as responding CD4 T cells from children produced less IFNγ and were less likely to express multiple cytokines. These differences in the repertoire of influenza-specific CD4 T cells available for recall on influenza challenge in early childhood could possibly contribute to early imprinting of influenza-specific immunity as well as the increased susceptibility of children to this viral infection.

Population Serologic Immunity to Human and Avian H2N2 Viruses in the United States and Hong Kong for Pandemic Risk Assessment.

Background: Influenza A pandemics cause significant mortality and morbidity. H2N2 viruses have caused a prior pandemic, and are circulating in avian reservoirs. The age-related frequency of current population immunity to H2 viruses was evaluated. Methods: Hemagglutinin inhibition (HAI) assays against historical human and recent avian influenza A(H2N2) viruses were performed across age groups in Rochester, New York, and Hong Kong, China. The impact of existing cross-reactive HAI immunity on the effective reproduction number was modeled. Results: One hundred fifty individual sera from Rochester and 295 from Hong Kong were included. Eighty-five percent of patients born in Rochester and Hong Kong before 1968 had HAI titers ≥1:40 against A/Singapore/1/57, and >50% had titers ≥1:40 against A/Berkeley/1/68. The frequency of titers ≥1:40 to avian H2N2 A/mallard/England/727/06 and A/mallard/Netherlands/14/07 in subjects born before 1957 was 62% and 24%, respectively. There were no H2 HAI titers >1:40 in individuals born after 1968. These levels of seroprevalence reduce the initial reproduction number of A/Singapore/1/1957 or A/Berkeley/1/68 by 15%-20%. A basic reproduction number (R0) of the emerging transmissible virus <1.2 predicts a preventable pandemic. Conclusions: Population immunity to H2 viruses is insufficient to block epidemic spread of H2 virus. An H2N2 pandemic would have lower impact in those born before 1968.

Overarching Immunodominance Patterns and Substantial Diversity in Specificity and Functionality in the Circulating Human Influenza A and B Virus-Specific CD4+ T-Cell Repertoire.

There is limited information on the antigen specificity and functional potential of the influenza virus-specific CD4+ T-cell repertoire in humans. Here, enzyme-linked immunospot assays were used to examine circulating CD4+ T-cell specificities for influenza virus directly ex vivo in healthy adults. Our studies revealed CD4+ T-cell reactivity to multiple influenza virus proteins, including hemagglutinins, neuraminidases, M1 proteins, and nucleoproteins. Unexpectedly, the immunodominance hierarchies and functional potential of cells reactive toward influenza A virus were distinct from those toward influenza B virus. We also identified influenza virus-specific cells producing granzyme B. Our findings revealed individual and virus-specific patterns that may differentially poise humans to respond to infection or vaccination.

Safety and Immunogenicity of a Recombinant Influenza Vaccine: A Randomized Trial.

OBJECTIVES: The recombinant influenza vaccine is well established in adults ≥18 years of age for preventing seasonal influenza disease. In this randomized controlled trial, we compared the safety and immunogenicity of the quadrivalent, recombinant influenza vaccine (RIV4) versus the inactivated influenza vaccine in children and adolescents 6 to 17 years of age. METHODS: Two age cohorts were enrolled sequentially: 159 subjects aged 9 to 17 years and, after reviewing for safety, 60 children aged 6 to 8 years. Enrollment of the younger children was halted prematurely at the onset of the influenza season. Subjects in each cohort were randomly assigned 1:1 to the RIV4 or inactivated vaccine. Hemagglutination inhibition antibody titers were obtained before and 28 days after vaccination. Tolerability and safety were monitored for 7 days and 6 months after vaccination, respectively. RESULTS: Both vaccines were well tolerated in both age groups, and long-term follow-up revealed no vaccine-related adverse events. Overall, immunogenicity (geometric mean titers and seroconversion rate differences) provided comparable antibody responses to most antigens in both vaccines in the older subjects. Low responses to the influenza B Victoria lineage in both vaccines made interpretation difficult. Immunogenicity in younger children was similar, but the truncated sample size was insufficient to support noninferiority comparisons. CONCLUSIONS: Despite low responses to influenza B lineages in both vaccines, the RIV4 provided safety and immunogenicity that were comparable to those of the licensed inactivated vaccine in pediatric subjects, which was most convincing in those aged 9 to 17 years. Future confirmatory clinical efficacy trials may be used to support the recombinant influenza vaccine as an alternative for the pediatric age group of ≥6 years.

Broad cross-reactive IgG responses elicited by adjuvanted vaccination with recombinant influenza hemagglutinin (rHA) in ferrets and mice.

Annual immunization against influenza virus is a large international public health effort. Accumulating evidence suggests that antibody mediated cross-reactive immunity against influenza hemagglutinin (HA) strongly correlates with long-lasting cross-protection against influenza virus strains that differ from the primary infection or vaccination strain. However, the optimal strategies for achieving highly cross-reactive antibodies to the influenza virus HA have not yet to be defined. In the current study, using Luminex-based mPlex-Flu assay, developed by our laboratory, to quantitatively measure influenza specific IgG antibody mediated cross-reactivity, we found that prime-boost-boost vaccination of ferrets with rHA proteins admixed with adjuvant elicited higher magnitude and broader cross-reactive antibody responses than that induced by actual influenza viral infection, and this cross-reactive response likely correlated with increased anti-stalk reactive antibodies. We observed a similar phenomenon in mice receiving three sequential vaccinations with rHA proteins from either A/California/07/2009 (H1N1) or A/Hong Kong/1/1968 (H3N2) viruses admixed with Addavax, an MF59-like adjuvant. Using this same mouse vaccination model, we determined that Addavax plays a more significant role in the initial priming event than in subsequent boosts. We also characterized the generation of cross-reactive antibody secreting cells (ASCs) and memory B cells (MBCs) when comparing vaccination to viral infection. We have also found that adjuvant plays a critical role in the generation of long-lived ASCs and MBCs cross-reactive to influenza viruses as a result of vaccination with rHA of influenza virus, and the observed increase in stalk-reactive antibodies likely contributes to this IgG mediated broad cross-reactivity.

A Highly Potent and Broadly Neutralizing H1 Influenza-Specific Human Monoclonal Antibody.

Influenza's propensity for antigenic drift and shift, and to elicit predominantly strain specific antibodies (Abs) leaves humanity susceptible to waves of new strains with pandemic potential for which limited or no immunity may exist. Subsequently new clinical interventions are needed. To identify hemagglutinin (HA) epitopes that if targeted may confer universally protective humoral immunity, we examined plasmablasts from a subject that was immunized with the seasonal influenza inactivated vaccine, and isolated a human monoclonal Ab (mAb), KPF1. KPF1 has broad and potent neutralizing activity against H1 influenza viruses, and recognized 83% of all H1 isolates tested, including the pandemic 1918 H1. Prophylactically, KPF1 treatment resulted in 100% survival of mice from lethal challenge with multiple H1 influenza strains and when given as late as 72 h after challenge with A/California/04/2009 H1N1, resulted in 80% survival. KPF1 recognizes a novel epitope in the HA globular head, which includes a highly conserved amino acid, between the Ca and Cb antigenic sites. Although recent HA stalk-specific mAbs have broader reactivity, their potency is substantially limited, suggesting that cocktails of broadly reactive and highly potent HA globular head-specific mAbs, like KPF1, may have greater clinical feasibility for the treatment of influenza infections.

Influence of Birth Cohort on Effectiveness of 2015-2016 Influenza Vaccine Against Medically Attended Illness Due to 2009 Pandemic Influenza A(H1N1) Virus in the United States.

Background: The effectiveness of influenza vaccine during 2015-2016 was reduced in some age groups as compared to that in previous 2009 pandemic influenza A(H1N1) virus (A[H1N1]pdm09 virus)-predominant seasons. We hypothesized that the age at first exposure to specific influenza A(H1N1) viruses could influence vaccine effectiveness (VE). Methods: We estimated the effectiveness of influenza vaccine against polymerase chain reaction-confirmed influenza A(H1N1)pdm09-associated medically attended illness from the 2010-2011 season through the 2015-2016 season, according to patient birth cohort using data from the Influenza Vaccine Effectiveness Network. Birth cohorts were defined a priori on the basis of likely immunologic priming with groups of influenza A(H1N1) viruses that circulated during 1918-2015. VE was calculated as 100 × [1 - adjusted odds ratio] from logistic regression models comparing the odds of vaccination among influenza virus-positive versus influenza test-negative patients. Results: A total of 2115 A(H1N1)pdm09 virus-positive and 14 696 influenza virus-negative patients aged ≥6 months were included. VE was 61% (95% confidence interval [CI], 56%-66%) against A(H1N1)pdm09-associated illness during the 2010-2011 through 2013-2014 seasons, compared with 47% (95% CI, 36%-56%) during 2015-2016. During 2015-2016, A(H1N1)pdm09-specific VE was 22% (95% CI, -7%-43%) among adults born during 1958-1979 versus 61% (95% CI, 54%-66%) for all other birth cohorts combined. Conclusion: Findings suggest an association between reduced VE against influenza A(H1N1)pdm09-related illness during 2015-2016 and early exposure to specific influenza A(H1N1) viruses.