The human antibody response to influenza A virus infection and vaccination

Ag-coated Au nanostar-based Lateral Flow Immunoassay for Highly Sensitive Influenza A virus antibody Detection in Colorimetric and Surface-Enhanced Raman Scattering (SERS) modes

Antibody testing for virus aids diagnosis, promotes vaccination and development, and evaluates antibody treatment efficacy. Hence, it is essential to examine and monitor antibody levels for accurate disease diagnosis and prevention. Lateral Flow Immunoassay (LFIA) is a technique that is known for its simplicity and speed, making it a popular choice for immediate detection. Noble metal nanoparticles are extensively employed in LFIA due to their exceptional colorimetric and Raman properties, which are a result of the LSPR effect. Au nanostars (Au NSs) have excellent SERS properties due to multiple sharp branches and more "hot spots" on the surface, while Ag nanoparticles (Ag NPs) have higher extinction coefficient and better refractive index sensitivity. The electromagnetic field strength on the surface of Ag-Au bimetallic nanomaterial is greatly enhanced, which further enhances the SERS intensity. In this work, we created a core-shell nanoparticle by combining Au NS as the core and Ag as the shell (Au NSMBA@Ag). We then inserted a Raman reporter molecule between the core and shell. Using this, we developed an LFIA platform that can detect influenza A virus antibodies in both colorimetric and Raman modes. The detection limit in colorimetric mode was 0.1 ng/mL, while in Raman mode it was 8.0 pg/mL, making it approximately 12 times more sensitive than the colorimetric mode. Furthermore, the method has shown excellent specificity, stability, and resistance to interference. Hence, this method can be applied to various fields such as environmental monitoring, clinical diagnosis, and food safety, showing great potential for future applications.

Binding and neutralising antibodies to respiratory syncytial virus and influenza A virus in serum and bronchoalveolar lavage fluid of healthy adults in the United States: A cross-sectional study

Using serum and bronchoalveolar lavage (BAL) fluid collected from 20 healthy adults (23-37 years, 55 % female) in the United States, we measured immunoglobulin (Ig) A, IgG, and neutralising activity against respiratory syncytial virus (RSV) and influenza A (H1N1) virus. RSV-binding IgA and IgG measurements in serum were positively correlated with those in BAL. For influenza A (H1N1) virus, serum and BAL IgA antibodies were positively correlated, whereas IgG antibodies did not show a significant correlation. RSV-specific and influenza A (H1N1)-specific neutralising activity did not correlate between serum and BAL samples. These results demonstrate virus-specific correlations between antibodies in the serum and BAL that may not necessarily reflect correlations in functional activity. Further work is needed to confirm our preliminary observations, and define the immune correlates of neutralising activity to these and other respiratory viruses in the lower respiratory tract.

COVID-19 infection is associated with an elevated risk for autoimmune blistering diseases while COVID-19 vaccination decreases the risk: A large-scale population-based cohort study of 112 million individuals

BACKGROUND

Numerous diseases associated with COVID-19 infection and vaccination have been reported, including conditions such as the autoimmune blistering diseases (AIBDs) pemphigus and pemphigoid. However, robust evidence supporting these associations is lacking.

OBJECTIVE

To investigate the risk of developing AIBD following COVID-19 infection and vaccination.

METHODS

Population-based retrospective cohort study utilizing data from over 112 million patients. The risk of AIBD within 3 months was compared among 3 cohorts: COVID-19 infection, COVID-19 vaccination, and controls, along with 7 sensitivity analyses.

RESULTS

COVID-19 infection was associated with an increased risk of AIBD (hazard ratio [HR] 1.508, 95% CI 1.260-1.805), with the risk being more pronounced for pemphigus (HR 2.432, 1.618-3.657) compared to bullous pemphigoid (HR 1.376, 1.019-1.857). Conversely, COVID-19 vaccination was associated with an almost halved risk of AIBD (HR 0.514, 0.394-0.672), with the risk reduction most significant for pemphigus (HR 0.477, 0.241-0.946). Comparisons between COVID-19 infection and vaccination revealed a more than threefold increased risk of AIBD in the infection cohort (HR 3.130, 2.411-4.063), particularly for pemphigus (HR 5.508, 2.973-10.205).

LIMITATIONS

Retrospective design and potential under-reporting of COVID-19 cases and vaccinations.

CONCLUSION

COVID-19 infection significantly increases the risk of AIBD while vaccination appears to reduce this risk.

SARS-CoV-2 infection primes cross-protective respiratory IgA in a MyD88- and MAVS-dependent manner

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is constantly evolving mutations in the Spike protein to evade humoral immunity. Respiratory tract antiviral IgA antibodies are superior to circulating IgG antibodies in preventing SARS-CoV-2 infection. However, the role of innate immune signals required for the induction of mucosal IgA against SARS-CoV-2 infection is unknown. Here we show that hamsters recovered from ancestral SARS-CoV-2 infection are cross-protected against heterologous SARS-CoV-2 alpha, gamma, delta, and omicron BA.1 variants. Intranasal vaccination with an inactivated whole virus vaccine completely protects hamsters against heterologous SARS-CoV-2 infection. In addition, we show that intranasal boost vaccination of mice recovered from SARS-CoV-2 infection with unadjuvanted Spike protein induces robust levels of respiratory anti-Spike IgA and protects the mice from a heterologous SARS-CoV-2 infection. Furthermore, our findings suggest that MyD88 and MAVS play a role in the induction of the memory IgA response following an intranasal booster with unadjuvanted Spike protein in mice recovered from the SARS-CoV-2 infection. These findings provide a useful basis for the development of cross-protective mucosal vaccines against heterologous SARS-CoV-2 infection.

Assessment of the prevalence of respiratory pathogens and the level of immunity to respiratory viruses in soldiers and civilian military employees in Poland

BACKGROUND

This study provides a detailed analysis of respiratory tract infections (RTIs) and immunity levels against influenza and SARS-CoV-2 among soldiers and military personnel in Poland. Owing to their unique service environments, this occupational group is at high risk. During deployments, they often face adverse physical conditions, close living quarters, and exposure to both local and endemic pathogens. It particularly increases their susceptibility to RTIs, which remain a leading cause of illness worldwide.

METHODS

The study cohort included 379 participants aged between 19 and 60 years. We used polymerase chain reaction (PCR) techniques to detect 34 common respiratory pathogens and analyzed blood serum samples to assess the degree of immunity against the influenza A, B, and SARS-CoV-2 viruses. In 78.10% of the participants, at least one respiratory pathogen was detected.

RESULTS

Human rhinovirus (HRV) was the most common (8.71%), followed by SARS-CoV-2 (4.75%) and influenza A (H1N1) sw (2.90%). Staphylococcus aureus was the most prevalent bacterial pathogen (18.47%), with significant occurrences of Haemophilus influenzae (14.24%) and Klebsiella pneumoniae (9.76%). Additionally, 52.3% of those with coinfections had combinations of bacterial and viral pathogens, highlighting the complexity of diagnosing and managing these infections. We also assessed immunity levels, which focused on antibodies specific to influenza A/B and SARS-CoV-2 viruses. For all the results obtained, statistical analyses were performed. A weak positive correlation between age and levels of anti-influenza antibodies was observed, suggesting a slight increase in antibody levels with age. A total of 81.53% of the participants had received at least one dose of the SARS-CoV-2 vaccine. A significant correlation between the number of vaccine doses and higher anti-SARS-CoV-2 IgG antibodies was observed, indicating stronger immunity with more vaccinations.

CONCLUSIONS

This study underscores the importance of specialized health monitoring and preventive measures such as vaccinations to protect military personnel from RTIs and maintain their operational readiness. The detailed analysis of pathogen prevalence and immunity levels offers valuable insights into this occupational group's health risks and needs.

CLINICAL TRIAL NUMBER

Not applicable.

Intranasal recombinant protein subunit vaccine targeting TLR3 induces respiratory tract IgA and CD8 T cell responses and protects against respiratory virus infection

BACKGROUND

Intranasal vaccines against respiratory viruses are desired due to ease of administration and potential to protect against virus infection of the upper respiratory tract.

METHODS

We tested a cationic liposomal adjuvant delivering the TLR3 agonist Poly (I:C) (CAF®09b) for intranasal administration, by formulating this with SARS-CoV-2 spike trimeric protein and assessing airway mucosal immune responses in mice. The vaccine was further evaluated in SARS-CoV-2 virus challenge models, using mice expressing the human ACE2 receptor and Syrian hamsters.

FINDINGS

The intranasal vaccine elicited both serum neutralising antibody responses and IgA responses in the upper respiratory tract. Uniquely, it also elicited high-magnitude CD4 and CD8 T cell responses in the lung parenchyma and nasal-associated lymphoid tissue. In contrast, parenteral administration of the same vaccine, or the mRNA-1273 (Spikevax®) vaccine, led to systemic antibody responses and vaccine-induced CD4 T cells were mainly found in circulation. The intranasal vaccine protected against homologous SARS-CoV-2 (Wuhan-Hu-1) challenge in K18-hACE2 mice, preventing weight loss and virus infection in the upper and lower airways. In Syrian hamsters, the vaccine prevented weight loss and significantly reduced virus load after challenge with the homologous strain and Omicron BA.5.

INTERPRETATION

This study demonstrates that intranasal subunit vaccines containing TLR3-stimulating cationic liposomes effectively induce airway IgA and T cell responses, which could be utilised in future viral pandemics.

FUNDING

This work was primarily supported by the European Union Horizon 2020 research and innovation program under grant agreement no. 101003653.

IFIT3 RNA-binding activity promotes influenza A virus infection and translation efficiency

Host cells produce a vast network of antiviral factors in response to viral infection. The interferon-induced proteins with tetratricopeptide repeats (IFITs) are important effectors of a broad-spectrum antiviral response. In contrast to their canonical roles, we previously identified IFIT2 and IFIT3 as pro-viral host factors during influenza A virus (IAV) infection. During IAV infection, IFIT2 binds and enhances translation of AU-rich cellular mRNAs, including many IFN-simulated gene products, establishing a model for its broad antiviral activity. But, IFIT2 also bound viral mRNAs and enhanced their translation resulting in increased viral replication. The ability of IFIT3 to bind RNA and whether this is important for its function was not known. Here we validate direct interactions between IFIT3 and RNA using electromobility shift assays (EMSAs). RNA-binding site identification (RBS-ID) experiments then identified an RNA-binding surface composed of residues conserved in IFIT3 orthologs and IFIT2 paralogs. Mutation of the RNA-binding site reduced the ability IFIT3 to promote IAV gene expression and translation efficiency when compared to wild type IFIT3. The functional units of IFIT2 and IFIT3 are homo- and heterodimers, however the RNA-binding surfaces are located near the dimerization interface. Using co-immunoprecipitation, we showed that mutations to these sites do not affect dimerization. Together, these data establish the link between IFIT3 RNA-binding and its ability to modulate translation of host and viral mRNAs during IAV infection.

Importance

Influenza A viruses (IAV) cause considerable morbidity and mortality through sporadic pandemics as well as annual epidemics. Zoonotic IAV strains pose an additional risk of spillover into a naive human population where prior immunity can have minimal effect. In this case, the first line of defense in the host is the innate immune response. Interferon stimulated genes (ISGs) produce a suite of proteins that are front-line effectors of innate immune responses. While ISGs are typically considered antiviral, new work has revealed an emerging trend where viruses co-opt ISGs for pro-viral function. Here, we determine how the ISG IFIT3 is used by IAV as a pro-viral factor, advancing our understanding of IFIT3 function generally as well as specifically in the context of IAV infection.

Systems immunology analysis of human immune organoids identifies host-specific correlates of protection to different influenza vaccines

Vaccines are an essential tool to significantly reduce pathogen-related morbidity and mortality. However, our ability to rationally design vaccines and identify correlates of protection remains limited. Here, we employed an immune organoid approach to capture human adaptive immune response diversity to influenza vaccines and systematically identify host and antigen features linked to vaccine response variability. Our investigation identified established and unique immune signatures correlated with neutralizing antibody responses across seven different influenza vaccines and antigens. Unexpectedly, heightened ex vivo tissue frequencies of T helper (Th)1 cells emerged as both a predictor and a correlate of neutralizing antibody responses to inactivated influenza vaccines (IIVs). Secondary analysis of human public data confirmed that elevated Th1 signatures are associated with antibody responses following in vivo vaccination. These findings demonstrate the utility of human in vitro models for identifying in vivo correlates of protection and establish a role for Th1 functions in influenza vaccination.

MAGPIE: A Machine Learning Approach to Decipher Protein-Protein Interactions in Human Plasma

Immunoprecipitation coupled to tandem mass spectrometry (IP-MS/MS) methods are often used to identify protein-protein interactions (PPIs). While these approaches are prone to false positive identifications through contamination and antibody nonspecific binding, their results can be filtered using negative controls and computational modeling. However, such filtering does not effectively detect false-positive interactions when IP-MS/MS is performed on human plasma samples. Therein, proteins cannot be overexpressed or inhibited, and existing modeling algorithms are not adapted for execution without such controls. Hence, we introduce MAGPIE, a novel machine learning-based approach for identifying PPIs in human plasma using IP-MS/MS, which leverages negative controls that include antibodies targeting proteins not expected to be present in human plasma. A set of negative controls used for false positive interaction modeling is first constructed. MAGPIE then assesses the reliability of PPIs detected in IP-MS/MS experiments using antibodies that target known plasma proteins. When applied to five IP-MS/MS experiments as a proof of concept, our algorithm identified 68 PPIs with an FDR of 20.77%. MAGPIE significantly outperformed a state-of-the-art PPI discovery tool and identified known and predicted PPIs. Our approach provides an unprecedented ability to detect human plasma PPIs, which enables a better understanding of biological processes in plasma.

Structural mapping of polyclonal IgG responses to HA after influenza virus vaccination or infection

Cellular and molecular characterization of immune responses elicited by influenza virus infection and seasonal vaccination have informed efforts to improve vaccine efficacy, breadth, and longevity. Here, we use negative stain electron microscopy polyclonal epitope mapping (nsEMPEM) to structurally characterize the humoral IgG antibody responses to hemagglutinin (HA) from human patients vaccinated with a seasonal quadrivalent flu vaccine or infected with influenza A viruses. Our data show that both vaccinated and infected patients had humoral IgGs targeting highly conserved regions on both H1 and H3 subtype HAs, including the stem and anchor, which are targets for universal influenza vaccine design. Responses against H1 predominantly targeted the central stem epitope in infected patients and vaccinated donors, whereas head epitopes were more prominently targeted on H3. Responses against H3 were less abundant, but a greater diversity of H3 epitopes were targeted relative to H1. While our analysis is limited by sample size, on average, vaccinated donors responded to a greater diversity of epitopes on both H1 and H3 than infected patients. These data establish a baseline for assessing polyclonal antibody responses in vaccination and infection, providing a context for future vaccine trials and emphasizing the need for further characterization of protective responses toward conserved epitopes. (201 words)IMPORTANCESeasonal influenza viruses cause hundreds of thousands of deaths each year and up to a billion infections; under the proper circumstances, influenza A viruses with pandemic potential could threaten the lives of millions more. The variable efficacies of traditional influenza virus vaccines and the desire to prevent pandemic influenzas have motivated work toward finding a universal flu vaccine. Many promising universal flu vaccine candidates currently focus on guiding immune responses to highly conserved epitopes on the central stem of the influenza hemagglutinin viral fusion protein. To support the further development of these stem-targeting vaccine candidates, in this study, we use negative stain electron microscopy to assess the prevalence of central stem-targeting antibodies in individuals who were exposed to influenza antigens through traditional vaccination and/or natural infection during the 2018-2019 flu season.

Targets of influenza human T-cell response are mostly conserved in H5N1

Frequent recent spillovers of subtype H5N1 clade 2.3.4.4b highly pathogenic avian influenza (HPAI) virus into poultry and mammals, especially dairy cattle, including several human cases, increased concerns over a possible future pandemic. Here, we performed an analysis of epitope data curated in the Immune Epitope Database (IEDB). We found that the patterns of immunodominance of seasonal influenza viruses circulating in humans and H5N1 are similar. We further conclude that a significant fraction of the T-cell epitopes is conserved at a level associated with cross-reactivity between avian and seasonal sequences, and we further experimentally demonstrate extensive cross-reactivity in the most dominant T-cell epitopes curated in the IEDB. Based on these observations, and the overall similarity of the neuraminidase (NA) N1 subtype encoded in both HPAI and seasonal H1N1 influenza virus as well as cross-reactive group 1 HA stalk-reactive antibodies, we expect that a degree of pre-existing immunity is present in the general human population that could blunt the severity of human H5N1 infections.IMPORTANCEInfluenza A viruses (IAVs) cause pandemics that can result in millions of deaths. The highly pathogenic avian influenza (HPAI) virus of the H5N1 subtype is presently among the top viruses of pandemic concern, according to the WHO and the National Institute of Allergy and Infectious Diseases (NIAID). Previous exposure by infection and/or vaccination to a given IAV subtype or clade influences immune responses to a different subtype or clade. Analysis of human CD4 and CD8 T-cell epitope conservation between HPAI H5N1 and seasonal IAV sequences revealed levels of identity and conservation conducive to T cell cross-reactivity, suggesting that pre-existing T cell immune memory should, to a large extent, cross-recognize avian influenza viruses. This observation was experimentally verified by testing responses from human T cells to non-avian IAV and their HPAI H5N1 counterparts. Accordingly, should a more widespread HPAI H5N1 outbreak occur, we hypothesize that cross-reactive T-cell responses might be able to limit disease severity.

Delay of innate immune responses following influenza B virus infection affects the development of a robust antibody response in ferrets

Due to its natural influenza susceptibility, clinical signs, transmission, and similar sialic acid residue distribution, the ferret is the primary animal model for human influenza research. Antibodies generated following infection of ferrets with human influenza viruses are used in surveillance to detect antigenic drift and cross-reactivity with vaccine viruses and circulating strains. Inoculation of ferrets, with over 1,500 human clinical influenza isolates (1998-2019) resulted in lower antibody responses (HI <1:160) to 86% (387 out of 448) influenza B viruses (IBVs) compared to 2.7% (30 out of 1,094) influenza A viruses (IAVs). Here, we show that the immune responses in ferrets inoculated with IBV were delayed and reduced compared to IAV. Innate gene expression in the upper respiratory tract and blood indicated that IAV generated a strong inflammatory response, including an early activation of the interferon (IFN), whereas IBV elicited a delayed and reduced response. Serum levels of cytokines and IFNs were all much higher following IAV infection than IBV infection. Pro-inflammatory, IFN, TH1/TH2, and T-effector proteins were significantly higher in sera of IAV-infected than IBV-infected ferrets over 28 days following the challenge. Serum levels of Type-I/II/III IFNs were detected following IAV infection throughout this period, whereas Type-III IFN was only late for IBV. An early increase in IFN-lambda corresponded to gene expression following IAV infection. Reduced innate immune responses following IBV infection reflected the subsequent delayed and reduced serum antibodies. These findings may help in understanding the antibody responses in humans following influenza vaccination or infection and consideration of potential addition of innate immunomodulators to overcome low responses.

IMPORTANCE

The ferret is the primary animal model for human influenza research. Using a ferret model, we studied the differences in both innate and adaptive immune responses following infection with influenza A and B viruses (IAV and IBV). Antibodies generated following infection of ferrets is used for surveillance assays to detect antigenic drift and cross-reactivity with vaccine viruses and circulating influenza strains. IAV infection of ferrets to generate these reagents resulted in a strong antibody response, but IBV infection generated weak antibody responses. In this study using influenza-infected ferrets, we found that IAV resulted in an early activation of the interferon (IFN) and pro-inflammatory response, whereas IBV showed a delay and reduction in these responses. Serum levels of IFNs and other cytokines or chemokines were much higher in ferrets following IAV infection. These reduced innate responses were reflected the subsequent delayed and reduced antibody responses to IBV in the sera. These findings may help in understanding low antibody responses in humans following influenza B vaccination and infection and may warrant the use of innate immunomodulators to overcome these weak responses.

Are we serologically prepared against an avian influenza pandemic and could seasonal flu vaccines help us?

The current situation with H5N1 highly pathogenic avian influenza virus (HPAI) is causing a worldwide concern due to multiple outbreaks in wild birds, poultry, and mammals. Moreover, multiple zoonotic infections in humans have been reported. Importantly, HPAI H5N1 viruses with genetic markers of adaptation to mammals have been detected. Together with HPAI H5N1, avian influenza viruses H7N9 (high and low pathogenic) stand out due to their high mortality rates in humans. This raises the question of how prepared we are serologically and whether seasonal vaccines are capable of inducing protective immunity against these influenza subtypes. An observational study was conducted in which sera from people born between years 1925-1967, 1968-1977, and 1978-1997 were collected before or after 28 days or 6 months post-vaccination with an inactivated seasonal influenza vaccine. Then, hemagglutination inhibition, viral neutralization, and immunoassays were performed to assess the basal protective immunity of the population as well as the ability of seasonal influenza vaccines to induce protective responses. Our results indicate that subtype-specific serological protection against H5N1 and H7N9 in the representative Spanish population evaluated was limited or nonexistent. However, seasonal vaccination was able to increase the antibody titers to protective levels in a moderate percentage of people, probably due to cross-reactive responses. These findings demonstrate the importance of vaccination and suggest that seasonal influenza vaccines could be used as a first line of defense against an eventual pandemic caused by avian influenza viruses, to be followed immediately by the use of more specific pandemic vaccines.IMPORTANCEInfluenza A viruses (IAV) can infect and replicate in multiple mammalian and avian species. Avian influenza virus (AIV) is a highly contagious viral disease that occurs primarily in poultry and wild water birds. Due to the lack of population immunity in humans and ongoing evolution of AIV, there is a continuing risk that new IAV could emerge and rapidly spread worldwide, causing a pandemic, if the ability to transmit efficiently among humans was gained. The aim of this study is to analyze the basal protection and presence of antibodies against IAV H5N1 and H7N9 subtypes in the population from different ages. Moreover, we have evaluated the humoral response after immunization with a seasonal influenza vaccine. This study is strategically important to evaluate the level of population immunity that is a major factor when assessing the impact that an emerging IAV strain would have, and the role of seasonal vaccines to mitigate the effects of a pandemic.

Inverted HA-EV immunization elicits stalk-specific influenza immunity and cross-protection in mice

Enhancing protective immunity in the respiratory tract is crucial to combat influenza infection and transmission. Developing mucosal universal influenza vaccines requires effective delivery platforms to overcome the respiratory mucosal barrier and stimulate appropriate innate immune reactions, thereby bridging adaptive immune responses with minimal necessary inflammation. Meanwhile, the vaccine platforms must be biocompatible. This study employed cell-derived extracellular vesicles (EVs) as a mucosal universal influenza vaccine platform. By conjugating influenza hemagglutinin (HA) onto EV surfaces through HA-receptor interaction, we achieved an upside-down (inverted) influenza HA configuration that exposed the conserved HA stalk region while partially hiding the globular head domain. Intranasal immunization with the resulting EVs induced robust HA stalk- and virus-specific serum antibody and mucosal immune responses in mice, protecting against heterologous virus infection. Notably, EVs derived from the lung epithelial cell line A549 induced superior cross-reactive antibodies and enhanced protection upon intranasal immunization. EVs conjugating multivalent HA elicited broadly cross-reactive antibody and cellular responses against different influenza strains. Our results demonstrated that EVs conjugating multiple inverted HAs represented an effective strategy for developing a mucosal universal influenza vaccine.

Cross-protection against homo and heterologous influenza viruses via intranasal administration of an HA chimeric multiepitope nanoparticle vaccine

BACKGROUND

Influenza A viruses (IAVs) cause seasonal influenza epidemics and pose significant threats to public health. However, seasonal influenza vaccines often elicit strain-specific immune responses and confer little protection against mismatched strains. There is an urgent need to develop universal influenza vaccines against emerging and potentially re-emerging influenza virus infections. Multiepitope vaccines combining multiple conserved epitopes can induce more robust and broader immune responses and provide a potential solution.

RESULTS

Here, we demonstrated that an HA chimeric multiepitope nanoparticle vaccine, delivered intranasally conferred broad protection against challenges with various influenza viruses in mice. The nanoparticle vaccine co-expresses the ectodomain of haemagglutinin (H), three repeated highly conserved ectodomains of matrix protein 2 (M), and the M-cell-targeting ligand Co4B (C) in a baculovirus-insect cell system. These elements (C, H and M) were presented on the surface of self-assembling ferritin (f) in tandem to generate a nanoparticle denoted as CHM-f. Intranasal vaccination with CHM-f nanoparticles elicited robust humoral and cellular immune responses, conferring complete protection against a variety of IAVs, including the A/PR8/34 H1N1 strain, the swine flu H3N2 strain, the avian flu H5N8 strain, and H9N2. When CHM-f nanoparticles adjuvanted with CpG IAMA-002, the weight loss protective effect, cellular immune responses and mucosal IgA responses were significantly augmented. Compared with controls, mice immunized with CHM-f nanoparticles with or without CpG IAMA-002 showed significant reductions in weight loss, lung viral titres and pathological changes.

CONCLUSIONS

These results suggest that CHM-f nanoparticle with or without CpG IAMA-002 is a promising candidate as a universal influenza vaccine.

Differential antigenic imprinting effects between influenza H1N1 hemagglutinin and neuraminidase in a mouse model

Understanding how immune history influences influenza immunity is essential for developing effective vaccines and therapeutic strategies. This study examines the antigenic imprinting of influenza hemagglutinin (HA) and neuraminidase (NA) using a mouse model with sequential infections by H1N1 virus strains exhibiting substantial antigenic differences in HA. In our pre-2009 influenza infection model, we observed that mice with more extensive infection histories produced higher levels of functional NA-inhibiting antibodies (NAI). However, following further infection with the 2009 pandemic H1N1 strain, these mice demonstrated a reduced NAI to the challenged virus. Interestingly, prior exposure to older strains resulted in a lower HA antibody response (neutralization and HAI) to the challenged virus in both pre- and post-2009 scenarios, potentially due to faster viral clearance facilitated by immune memory recall. Overall, our findings reveal distinct trajectories in HA and NA immune responses, suggesting that immune imprinting can differentially impact these proteins based on the extent of antigenic variation in influenza viruses.

IMPORTANCE

Influenza viruses continue to pose a significant threat to human health, with vaccine effectiveness remaining a persistent challenge. Individual immune history is a crucial factor that can influence antibody responses to subsequent influenza exposures. While many studies have explored how pre-existing antibodies shape the induction of anti-HA antibodies following influenza virus infections or vaccinations, the impact on anti-NA antibodies has been less extensively studied. Using a mouse model, our study demonstrates that within pre-2009 H1N1 strains, an extensive immune history negatively impacted anti-HA antibody responses but enhanced anti-NA antibody responses. However, in response to the 2009 pandemic H1N1 strain, which experienced an antigenic shift, both anti-HA and anti-NA antibody responses were hindered by antibodies from prior pre-2009 H1N1 virus infections. These findings provide important insights into how antigenic imprinting affects both anti-HA and anti-NA antibody responses and underscore the need to consider immune history in developing more effective influenza vaccination strategies.

Adjuvant-free, self-assembling ferritin nanoparticle vaccine coupled with influenza virus hemagglutinin protein carrying M1 and PADRE epitopes elicits cross-protective immune responses

Introduction

Influenza viruses pose a significant threat to global public health. Several influenza pandemic outbreaks have had serious economic and public health implications. Current influenza virus vaccines generally provide strain-specific protection and must be rapidly produced annually to match the circulating viruses. Developing influenza vaccines that confer protection against a broad range of viruses will have a positive impact on public health. In this study, we aimed to develop a ferritin-based influenza nanoparticle vaccine with a broad protective spectrum to enhance the immune response against diverse influenza viruses.

Results

We generated an adjuvant-free, self-assembling nanoparticle vaccine against diverse influenza A viruses. This nanoparticle vaccine displayed multi-antigen targets on the surface of Helicobacter pylori ferritin, which consists of the ectodomain of hemagglutinin of the H3N2 virus and three tandem highly conserved influenza M1 epitopes fused with the universal helper T-cell epitope PADRE, named HMP-NP. HMP-NPs were expressed in a soluble form in the baculovirus-insect cell system and self-assembled into homogeneous nanoparticles. Animal immunization studies showed that the HMP-NP nanovaccine elicited 4-fold higher haemagglutination inhibition (HAI) titers than inactivated influenza vaccine. And neutralization titers induced by HMP-NPs against the H3N2 virus and heterologous strains of the H1N1 and H9N2 viruses were ~8, 12.4 and 16 times higher than inactivated influenza vaccine, respectively. Meanwhile, we also observed that the number of IFN-γ- and IL-4-secreting cells induced by HMP-NPs were ~2.5 times higher than inactivated influenza vaccine. Importantly, intranasal immunization with HMP-NPs, without any adjuvant, induced efficient mucosal IgA responses and conferred complete protection against the H3N2 virus, as well as partial protection against the H1N1 and H9N2 viruses and significantly reduced lung viral loads.

Discussion

Overall, our results indicated that the self-assembled nanovaccines increased the potency and breadth of the immune response against various influenza viruses and are a promising delivery platform for developing vaccines with broader protection against emerging influenza viruses and other pathogens.

Replication-incompetent VSV-based vaccine elicits protective responses against SARS-CoV-2 and influenza virus

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza viruses lead to severe respiratory illnesses and death in humans, exacerbated in individuals with underlying health conditions, remaining substantial global public health concerns. Here, we developed a bivalent replication-incompetent single-cycle pseudotyped vesicular stomatitis virus vaccine that incorporates both a prefusion-stabilized SARS-CoV-2 spike protein lacking a furin cleavage site and a full-length influenza A virus neuraminidase protein. Vaccination of K18-hACE2 or C57BL/6J mouse models generated durable levels of neutralizing antibodies, T cell responses, and protection from morbidity and mortality upon challenge with either virus. Furthermore, the vaccine provided heterologous protection upon challenge with a different influenza virus strain, supporting the advantage of using NA to increase the breadth of vaccine protection. Now, no bivalent vaccine is approved for use against both SARS-CoV-2 and influenza virus. Our study supports using this platform to develop safe and efficient vaccines against multiple viruses.

Human naïve B cells recognize prepandemic influenza virus hemagglutinins

Understanding the naïve B cell repertoire and its specificity for potential zoonotic threats, such as the highly pathogenic avian influenza (HPAI) H5Nx viruses, may allow prediction of infection- or vaccine-specific responses. However, this naïve repertoire and the possibility to respond to emerging, prepandemic viruses are largely undetermined. Here, we profiled naïve B cell reactivity against a prototypical HPAI H5 hemagglutinin (HA), the major target of antibody responses. We found that the frequency of H5-specific human naïve B cells targeting the HA "head" domain was increased relative to cross-reactive B cells to a circulating seasonal H1N1 strain. We classified the isolated monoclonal antibodies (mAbs) by the HA epitopes engaged and found that selected mAbs neutralized H5N1 at germline. We determined a cryo-electron microscopic structure of one mAb in complex with H5 HA to define its epitope. Our study defines the naïve human B cell repertoire recognizing a potentially zoonotic HPAI.

Integrative Mapping of Pre-existing Immune Landscapes for Vaccine Response Prediction

Predicting individual vaccine responses remains a significant challenge due to the complexity and variability of immune processes. To address this gap, we developed immunaut, an open-source, data-driven framework implemented as an R package specifically designed for all systems vaccinologists seeking to analyze and predict immunological outcomes across diverse vaccination settings. Leveraging one of the most comprehensive live attenuated influenza vaccine (LAIV) datasets to date - 244 Gambian children enrolled in a phase 4 immunogenicity study - immunaut integrates humoral, mucosal, cellular, transcriptomic, and microbiological parameters collected before and after vaccination, providing an unprecedentedly holistic view of LAIV-induced immunity. Through advanced dimensionality reduction, clustering, and predictive modeling, immunaut identifies distinct immunophenotypic responder profiles and their underlying baseline determinants. In this study, immunaut delineated three immunophenotypes: (1) CD8 T-cell responders, marked by strong baseline mucosal immunity and extensive prior influenza virus exposure that boosts memory CD8 T-cell responses, without generating influenza virus-specific antibody responses; (2) Mucosal responders, characterized by pre-existing systemic influenza A virus immunity (specifically to H3N2) and stable epithelial integrity, leading to potent mucosal IgA expansions and subsequent seroconversion to influenza B virus; and (3) Systemic, broad influenza A virus responders, who start with relatively naive immunity and leverage greater initial viral replication to drive broad systemic antibody responses against multiple influenza A virus variants beyond those included in the LAIV vaccine. By integrating pathway-level analysis, model-derived contribution scores, and hierarchical decision rules, immunaut elucidates how distinct immunological landscapes shape each response trajectory and how key baseline features, including pre-existing immunity, mucosal preparedness, and cellular support, dictate vaccine outcomes. Collectively, these findings emphasize the power of integrative, predictive frameworks to advance precision vaccinology, and highlight immunaut as a versatile, community-available resource for optimizing immunization strategies across diverse populations and vaccine platforms.

SARS-CoV-2 vaccine based on ferritin complexes with screened immunogenic sequences from the Fv-antibody library

In this study, the vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was developed using ferritin complexes with the immunogenic sequences screened against the SARS-CoV-2 spike protein (SP) from the Fv-antibody library. The Fv-antibody library was prepared on the outer membrane of E. coli by the expression of the VH region of immunoglobulin G (IgG) with a randomized complementarity-determining region 3 (CDR3). Four Fv-antibodies to the receptor-binding domain (RBD) were screened from the Fv-antibody library, which had a comparable binding constant (KD) between SARS-CoV-2 SP and the angiotensin-converting enzyme 2 (ACE2) receptor. The binding sites of screened Fv-antibodies on the RBD were analyzed using a docking analysis, and these binding sites were used as immunogenic sequences for the vaccine. The four immunogenic sequences were modified and co-expressed as a part of ferritin which was assembled into a ferritin complex. After the vaccination of ferritin complexes to mice, the anti-sera were analyzed to have a high enough titer. Additionally, the immune responses were found to be activated by vaccination, such as the expression of IgG subclasses and the increased level of cytokines. The neutralizing activity of the anti-sera was estimated using a cell-based infection assay based on pseudo-virus expressing the SP of SARS-CoV-2 variants.

Influenza A virus in dairy cattle: infection biology and potential mammary gland-targeted vaccines

Influenza, a major "One Health" threat, has gained heightened attention following recent reports of highly pathogenic avian influenza in dairy cattle and cow-to-human transmission in the USA. This review explores general aspects of influenza A virus (IAV) biology, its interactions with mammalian hosts, and discusses the key considerations for developing vaccines to prevent or curtail IAV infection in the bovine mammary gland and its spread through milk.

Influenza A Virus H7 nanobody recognizes a conserved immunodominant epitope on hemagglutinin head and confers heterosubtypic protection

Influenza remains a persistent global health challenge, largely due to the virus' continuous antigenic drift and occasional shift, which impede the development of a universal vaccine. To address this, the identification of broadly neutralizing antibodies and their epitopes is crucial. Nanobodies, with their unique characteristics and binding capacity, offer a promising avenue to identify such epitopes. Here, we isolate and purify a hemagglutinin (HA)-specific nanobody that recognizes an H7 subtype of influenza A virus. The nanobody, named E10, exhibits broad-spectrum binding, cross-group neutralization and in vivo protection across various influenza A subtypes. Through phage display and in vitro characterization, we demonstrate that E10 specifically targets an epitope on HA head which is part of the conserved lateral patch and is highly immunodominant upon H7 infection. Importantly, immunization with a peptide including the E10 epitope elicits cross-reactive antibodies and mediates partial protection from lethal viral challenge. Our data highlights the potential of E10 and its associated epitope as a candidate for future influenza prevention strategies.

Mucosal immune response in biology, disease prevention and treatment

The mucosal immune system, as the most extensive peripheral immune network, serves as the frontline defense against a myriad of microbial and dietary antigens. It is crucial in preventing pathogen invasion and establishing immune tolerance. A comprehensive understanding of mucosal immunity is essential for developing treatments that can effectively target diseases at their entry points, thereby minimizing the overall impact on the body. Despite its importance, our knowledge of mucosal immunity remains incomplete, necessitating further research. The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has underscored the critical role of mucosal immunity in disease prevention and treatment. This systematic review focuses on the dynamic interactions between mucosa-associated lymphoid structures and related diseases. We delve into the basic structures and functions of these lymphoid tissues during disease processes and explore the intricate regulatory networks and mechanisms involved. Additionally, we summarize novel therapies and clinical research advances in the prevention of mucosal immunity-related diseases. The review also addresses the challenges in developing mucosal vaccines, which aim to induce specific immune responses while maintaining tolerance to non-pathogenic microbes. Innovative therapies, such as nanoparticle vaccines and inhalable antibodies, show promise in enhancing mucosal immunity and offer potential for improved disease prevention and treatment.

Dynamic modeling of antibody repertoire reshaping in response to viral infections

For decades, research has largely focused on the generation of high-affinity, antigen-specific antibodies during viral infections. This emphasis has made it challenging for immunologists to systematically evaluate the mechanisms initiating humoral immunity in specific immune responses. In this study, we employ ordinary differential equations (ODE) to investigate the dynamic reshaping of the entire antibody repertoire in response to viral infections. Our findings demonstrate that the host's antibody atlas undergoes significant restructuring during these infections by the selective expansion of antibody pools with strong binding activity. The simulation results indicate that the ELISA (Enzyme-Linked Immunosorbent Assay) outcomes do not directly reflect the levels of specific neutralizing antibodies, but rather represent a quantitative response of the reshaped antibody repertoire following infection. Our model transcends traditional theories of immune memory, providing an explanation for the sustained presence of specific antibodies in the human body in long term. Additionally, our model extends to explore the mechanistic basis of the original antigenic sin, providing practical applications of our framework. One important application of this model is that it indicates that antibodies with a faster forward binding rate are more effective in preventing and treating associated viral infections compared to those with higher binding affinity.

Poor vaccine responders mask the true trend in vaccine effectiveness against progression to severe disease

Vaccines can reduce an individual's risk of infection and their risk of progression to severe disease given infection. The latter effect is less commonly estimated but is relevant for vaccine impact modeling and cost-effectiveness calculations. Using a motivating example from the COVID-19 literature, we note how vaccine effectiveness against progression to severe disease can appear to increase from below 0 % to over 70 % within 8 months. With true biological strengthening of this magnitude being unlikely, we use a mathematical modeling framework to identify parameter combinations where this phenomenon can occur. Fundamental features are an immunocompetent population with high initial protection against infection, contrasted with a vulnerable subpopulation with poor vaccine response against infection and progression. As a result, the earliest infections are among those with the weakest protection against severe disease. This work highlights methodological challenges in isolating a vaccine's effect on progression to severe disease after infection, and it signals the need for refined analytical methods to adjust for differences between the vaccinated infected and the unvaccinated infected populations.

LL-37, the master antimicrobial peptide, its multifaceted role from combating infections to cancer immunity

Antimicrobial peptides (AMPs) represent a unique group of naturally occurring molecules having diverse biological activities, including potent antimicrobial properties. Among them, LL-37 has emerged as a significant player, demonstrating its multifaceted roles during bacterial, fungal, and viral infections, as well as exhibiting intriguing implications in cancer. This review delves into the versatile functions of LL-37, elucidating its mechanisms of action against microbial pathogens and its potential to modulate immune responses. We explored the efficacy of LL-37 in disrupting bacterial membranes, inhibiting fungal growth, and interfering with viral replication, highlighting its potential as a therapeutic agent against a wide array of infectious diseases. Furthermore, we discussed the emerging role of LL-37 in cancer immunity, where its immunomodulatory effects and direct cytotoxicity towards cancer cells offer novel avenues for cancer therapy in the near future. We provided a comprehensive overview of the activities of LL-37 across various diseases and underscored the importance of further research into harnessing the therapeutic potential of this potential antimicrobial peptide along with other suitable candidates.

Understanding Influenza

Influenza, a serious illness of humans and domesticated animals, has been studied intensively for many years. It therefore provides an example of how much we can learn from detailed studies of an infectious disease, and of how even the most intensive scientific research leaves further questions to answer. This introduction is written for researchers who have become interested in one of these unanswered questions, but who may not have previously worked on influenza. To investigate these questions, researchers must not only have a firm grasp of relevant methods and protocols; they must also be familiar with the basic details of our current understanding of influenza. This chapter briefly covers the burden of disease that has driven influenza research, summarizes how our thinking about influenza has evolved over time, and sets out key features of influenza viruses by discussing how we classify them and what we currently understand of their replication. It does not aim to be comprehensive, as any researcher will read deeply into the specific areas that have grasped their interest. Instead, it aims to provide a general summary of how we came to think about influenza in the way we do now, in the hope that the reader's own research will help us to understand it better.

Hemagglutinin 3 and 8 can be the most efficient influenza subtypes for human host invasion; a comparative in silico approach

The severity of the influenza virus infection is largely determined by its ability to invade the human host receptor. This critical step is conducted by utilizing hemagglutinin (HA) due to its binding with sialic acid 2,6 (SA). Though 18 subtypes (H1-H18) of HA have been identified, the most efficient one for conducting the host entry has not yet been resolved. This study aims to assess the severity of infections for HA variants by conducting a comparative docking of H1-H18 with the human SA receptor. Eighteen viral 3D structures were retrieved, minimized, and optimized for docking with human SA. In all retrieved structures, five conserved amino acid residues were selected for docking with human SA. Special protein grids were prepared by locating these five residues in the 18 selected subtypes. Results showed that H3 and H8 exerted the highest standard precision and extra precision docking scores, and the highest binding affinities with the human SA, respectively. Phylogenetic analyses confirmed the actual positioning of the selected 3D structures and showed these docked structures belonged to their usual classes due to the extremely close distances found in each docked subtype compared with its corresponding non-docked structures. H8-SA showed slightly better RMSD and SASA values than H3-SA, while H3-SIA showed more favourable radius of gyration scores than H8-SIA in the majority of the simulation period. Due to the highest affinity of binding of H3 and H8 with the human receptor, special caution should be exercised regarding any possible outbreak mediated by these subtypes in human populations. However, it is important to acknowledge a limitation inherent to the computational approach; it may hold relative rather than absolute significance. Further research is needed to deepen our understanding of the intricate interplay between HA variants and the host receptor, taking into account the broader context of viral infection dynamics.Communicated by Ramaswamy H. Sarma.

SARS-CoV-2-specific plasma cells are not durably established in the bone marrow long-lived compartment after mRNA vaccination

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccines are effective at protecting from severe disease, but the protective antibodies wane rapidly even though SARS-CoV-2-specific plasma cells can be found in the bone marrow (BM). Here, to explore this paradox, we enrolled 19 healthy adults at 2.5-33 months after receipt of a SARS-CoV-2 mRNA vaccine and measured influenza-, tetanus- or SARS-CoV-2-specific antibody-secreting cells (ASCs) in long-lived plasma cell (LLPC) and non-LLPC subsets within the BM. Only influenza- and tetanus-specific ASCs were readily detected in the LLPCs, whereas SARS-CoV-2 specificities were mostly absent. The ratios of non-LLPC:LLPC for influenza, tetanus and SARS-CoV-2 were 0.61, 0.44 and 29.07, respectively. In five patients with known PCR-proven history of recent infection and vaccination, SARS-CoV-2-specific ASCs were mostly absent from the LLPCs. We show similar results with measurement for secreted antibodies from BM ASC culture supernatant. While serum IgG titers specific for influenza and tetanus correlated with IgG LLPCs, serum IgG levels for SARS-CoV-2, which waned within 3-6 months after vaccination, were associated with IgG non-LLPCs. In all, our studies suggest that rapid waning of SARS-CoV-2-specific serum antibodies could be accounted for by the absence of BM LLPCs after these mRNA vaccines.

Inactivated influenza virus vaccines expressing COBRA hemagglutinin elicited broadly reactive, long-lived protective antibodies

The influenza viruses cause seasonal respiratory illness that affect millions of people globally every year. Prophylactic vaccines are the recommended method to prevent the breakout of influenza epidemics. One of the current commercial influenza vaccines consists of inactivated viruses that are selected months prior to the start of a new influenza season. In many seasons, the vaccine effectiveness (VE) of these vaccines can be relatively low. Therefore, there is an urgent need to develop an improved, more universal influenza vaccine (UIV) that can provide broad protection against various drifted strains in all age groups. To meet this need, the computationally optimized broadly reactive antigen (COBRA) methodology was developed to design a hemagglutinin (HA) molecule as a new influenza vaccine. In this study, COBRA HA-based inactivated influenza viruses (IIV) expressing the COBRA HA from H1 or H3 influenza viruses were developed and characterized for the elicitation of immediate and long-term protective immunity in both immunologically naïve or influenza pre-immune animal models. These results were compared to animals vaccinated with IIV vaccines expressing wild-type H1 or H3 HA proteins (WT-IIV). The COBRA-IIV elicited long-lasting broadly reactive antibodies that had hemagglutination-inhibition (HAI) activity against drifted influenza variants.

Detection and Phylogenetic Characterization of Influenza D in Swedish Cattle

Increased evidence suggests that cattle are the primary host of Influenza D virus (IDV) and may contribute to respiratory disease in this species. The aim of this study was to detect and characterise IDV in the Swedish cattle population using archived respiratory samples. This retrospective study comprised a collection of a total 1763 samples collected between 1 January 2021 and 30 June 2024. The samples were screened for IDV and other respiratory pathogens using real-time reverse transcription quantitative PCR (rRT-qPCR). Fifty-one IDV-positive samples were identified, with a mean cycle threshold (Ct) value of 27 (range: 15-37). Individual samples with a Ct value of <30 for IDV RNA were further analysed by deep sequencing. Phylogenetic analysis was performed by the maximum likelihood estimation method on the whole IDV genome sequence from 16 samples. The IDV strains collected in 2021 (n = 7) belonged to the D/OK clade, whereas samples from 2023 (n = 4) and 2024 (n = 5) consisted of reassortants between the D/OK and D/660 clades, for the PB2 gene. This study reports the first detection of IDV in Swedish cattle and the circulation of D/OK and reassortant D/OK-D/660 in this population.

Elaborate Structural Modifications Yielding Novel Boron-Containing N-Substituted Oseltamivir Derivatives as Potent Neuraminidase Inhibitors with Significantly Improved Broad-Spectrum Antiresistance Profiles

Inspired by our previous finding that targeting the 150-cavity with a multisite-binding strategy emerged as an effective approach to obtain more potent and selective neuraminidase (NA) inhibitors against influenza virus, we present here the design, synthesis, and optimization of novel boron-containing N-substituted oseltamivir (OSC) derivatives. Exploratory structure-activity relationship (SAR) studies led to the identification of compounds 27c and 33c as the most potent NA inhibitors, surpassing OSC in potency against both wild-type group-1 NAs and oseltamivir-resistant NAs. These compounds demonstrated significant antiviral activity against several wild-type strains and H1N1pdm09 strains (EC50 = 0.03 ± 0.005 and 0.03 ± 0.0008 μM, respectively). Additionally, these compounds did not exhibit significant toxicity (CC50 > 200 μM in CEF cells; CC50 > 250 μM in MDCK cells). These findings highlight 27c and 33c as promising next-generation anti-influenza agents.

Durability of Adaptive Immunity in Immunocompetent and Immunocompromised Patients Across Different Respiratory Viruses: RSV, Influenza, and SARS-CoV-2

BACKGROUND/OBJECTIVES

Research on respiratory virus immunity duration post-vaccination reveals variable outcomes. This study performed a literature review to assess the efficacy and longevity of immune protection post-vaccination against SARS-CoV-2, influenza, and respiratory syncytial virus (RSV), with a focus on immunocompromised populations. Specific objectives included examining humoral and cellular immune responses and exploring the impact of booster doses and hybrid immunity on extending protection.

METHODS

A literature review was conducted focusing on studies published from January 2014 to November 2024. The search targeted adaptive immunity post-vaccination, natural immunity, and hybrid immunity for SARS-CoV-2, influenza, and RSV. Selection criteria emphasized human populations, adaptive immunity outcomes, and immunocompromised individuals. The PICO framework guided the analysis, culminating in a detailed review of 30 studies.

RESULTS

SARS-CoV-2 vaccines exhibited robust initial antibody responses, which waned significantly within six months, necessitating frequent boosters. Influenza and RSV vaccines similarly showed declines in immunity, though some influenza vaccines demonstrated moderate durability. Hybrid immunity, arising from combined natural infection and vaccination, provided more resilient and lasting protection than vaccination alone, especially against emerging variants. Immunocompromised individuals consistently exhibited reduced durability in adaptive immune responses across all studied viruses. Challenges include rapid viral mutations, limiting the broad protection of current vaccines.

CONCLUSIONS

Immune durability varies significantly across virus types and patient populations. Frequent boosters and hybrid immunity are critical to optimizing protection, particularly for vulnerable groups. The findings underscore the need for adaptable vaccination strategies and advancements in vaccine design to counter rapidly mutating respiratory pathogens effectively.

Calibration and comparison of SIR, SEIR/SLIR and SLAIR models for influenza dynamics: insights from the 2016-2017 season in the Valencian Community, Spain

Influenza and influenza-like illnesses pose significant challenges to healthcare systems globally. Mathematical models play a crucial role in understanding their dynamics, calibrating them to specific scenarios and making projections about their evolution over time. This study proposes a calibration process for three different but well-known compartmental models-SIR, SEIR/SLIR and SLAIR-using influenza data from the 2016-2017 season in the Valencian Community, Spain. The calibration process involves indirect calibration for the SIR and SLIR models, requiring post-processing to compare model output with data, while the SLAIR model is directly calibrated through direct comparison. Our calibration results demonstrate remarkable consistency between the SIR and SLIR models, with slight variations observed in the SLAIR model due to its unique design and calibration strategy. Importantly, all models align with existing evidence and intuitions found in the medical literature. Our findings suggest that at the onset of the epidemiological season, a significant proportion of the population (ranging from 29.08% to 43.75% of the total population) may have already entered the recovered state, likely due to immunization from the previous season. Additionally, we estimate that the percentage of infected individuals seeking healthcare services ranges from 5.7% to 12.2%. Through a well-founded and calibrated modeling approach, our study contributes to supporting, settling and quantifying current medical issues despite the inherent uncertainties involved in influenza dynamics. The full Mathematica code can be downloaded from https://munqu.webs.upv.es/software.html.

Humoral Correlates of Protection Against Influenza A/H3N2 Virus Infection

BACKGROUND

Influenza virus remains a threat to human health, but gaps remain in our knowledge of the humoral correlates of protection against influenza virus A/H3N2, limiting our ability to generate effective, broadly protective vaccines. The role of antibodies against the hemagglutinin (HA) stalk, a highly conserved but immunologically subdominant region, has not been established for influenza virus A/H3N2.

METHODS

Household transmission studies were conducted in Managua, Nicaragua, across 3 influenza seasons. Household contacts were tested for influenza virus infection using reverse-transcription polymerase chain reaction. We compared preexisting antibody levels against full-length HA, HA stalk, and neuraminidase (NA) measured by enzyme-linked immunosorbent assay, along with hemagglutination inhibition assay titers, between infected and uninfected participants.

RESULTS

A total of 899 individuals participated in household activation, with 329 infections occurring. A 4-fold increase in initial HA stalk titers was independently associated with an 18% decrease in the risk of infection (adjusted odds ratio [aOR], 0.82 [95% confidence interval {CI}, .68-.98]; P = .04). In adults, anti-HA stalk antibodies were independently associated with protection (aOR, 0.72 [95% CI, .54-.95]; P = .02). However, in 0- to 14-year-olds, anti-NA antibodies (aOR, 0.67 [95% CI, .53-.85]; P < .01) were associated with protection against infection, but anti-HA stalk antibodies were not.

CONCLUSIONS

The HA stalk is an independent correlate of protection against A/H3N2 infection, though this association is age dependent. Our results support the continued exploration of the HA stalk as a target for broadly protective influenza vaccines but suggest that the relative benefits may depend on age and influenza virus exposure history.

Reduced Effectiveness of Repeat Influenza Vaccination: Distinguishing Among Within-Season Waning, Recent Clinical Infection, and Subclinical Infection

Studies have reported that prior-season influenza vaccination is associated with higher risk of clinical influenza infection among vaccinees. This effect might arise from incomplete consideration of within-season waning and recent infection. Using data from the US Flu Vaccine Effectiveness Network (2011-2012 to 2018-2019 seasons), we found that repeat vaccinees were vaccinated earlier in a season by 1 week. After accounting for waning VE, we determined that repeat vaccinees were still more likely to test positive for A(H3N2) (odds ratio, 1.11; 95% CI, 1.02-1.21) but not influenza B or A(H1N1). We documented clinical infection influenced individuals' decision to vaccinate in the following season while protecting against clinical infection of the same type/subtype. However, adjusting for recent documented clinical infections did not strongly influence the estimated effect of prior-season vaccination. In contrast, we found that adjusting for subclinical or undocumented infection could theoretically attenuate this effect. Additional investigation is needed to determine the impact of subclinical infections on vaccine effectiveness.

Pathobiont-induced suppressive immune imprints thwart T cell vaccine responses

Pathobionts have evolved many strategies to coexist with the host, but how immune evasion mechanisms contribute to the difficulty of developing vaccines against pathobionts is unclear. Meanwhile, Staphylococcus aureus (SA) has resisted human vaccine development to date. Here we show that prior SA exposure induces non-protective CD4+ T cell imprints, leading to the blunting of protective IsdB vaccine responses. Mechanistically, these SA-experienced CD4+ T cells express IL-10, which is further amplified by vaccination and impedes vaccine protection by binding with IL-10Rα on CD4+ T cell and inhibit IL-17A production. IL-10 also mediates cross-suppression of IsdB and sdrE multi-antigen vaccine. By contrast, the inefficiency of SA IsdB, IsdA and MntC vaccines can be overcome by co-treatment with adjuvants that promote IL-17A and IFN-γ responses. We thus propose that IL-10 secreting, SA-experienced CD4+ T cell imprints represent a staphylococcal immune escaping mechanism that needs to be taken into consideration for future vaccine development.

Urban wastewater contains a functional human antibody repertoire of mucosal origin

Wastewater-based surveillance of human disease offers timely insights to public health, helping to mitigate infectious disease outbreaks and decrease downstream morbidity and mortality. These systems rely on nucleic acid amplification tests for monitoring disease trends, while antibody-based seroprevalence surveys gauge community immunity. However, serological surveys are resource-intensive and subject to potentially long lead times and sampling bias. We identified and characterized a human antibody repertoire, predominantly secretory IgA, isolated from a central wastewater treatment plant and building-scale wastewater collection points. These antibodies partition to the solids fraction and retain immunoaffinity for SARS-CoV-2 and Influenza A virus antigens. This stable pool could enable real-time tracking for correlates of vaccination, infection, and immunity, aiding in establishing population-level thresholds for immune protection and assessing the efficacy of future vaccine campaigns.

Concomitant administration of seasonal influenza and COVID-19 mRNA vaccines

Current clinical guidelines support the concomitant administration of seasonal influenza vaccines and COVID-19 mRNA boosters vaccine. Whether dual vaccination may impact vaccine immunogenicity due to an interference between influenza or SARS-CoV-2 antigens is unknown. We aimed to understand the impact of mRNA COVID-19 vaccines administered concomitantly on the immune response to influenza vaccines. For this, 128 volunteers were vaccinated during the 22-23 influenza season. Three groups of vaccination were assembled: FLU vaccine only (46, 35%) versus volunteers that received the mRNA bivalent COVID-19 vaccines concomitantly to seasonal influenza vaccines, FluCOVID vaccine in the same arm (42, 33%) or different arm (40, 31%), respectively. Sera and whole blood were obtained the day of vaccination, +7, and +28 days after for antibody and T cells response quantification. As expected, side effects were increased in individuals who received the FluCOVID vaccine as compared to FLU vaccine only based on the known reactogenicity of mRNA vaccines. In general, antibody levels were high at 4 weeks post-vaccination and differences were found only for the H3N2 virus when administered in different arms compared to the other groups at day 28 post-vaccination. Additionally, our data showed that subjects that received the FluCOVID vaccine in different arm tended to have better antibody induction than those receiving FLU vaccines for H3N2 virus in the absence of pre-existing immunity. Furthermore, no notable differences in the influenza-specific cellular immune response were found for any of the vaccination groups. Our data supports the concomitant administration of seasonal influenza and mRNA COVID-19 vaccines.

The added value of serologic testing: A comparison of influenza incidence among pregnant persons based on molecular-based surveillance versus serologic testing

BACKGROUND

We examined the added value of serologic testing for estimating influenza virus infection incidence based on illness surveillance with molecular testing versus periodic serologic testing.

METHODS

Pregnant persons unvaccinated against influenza at <28 weeks gestation were enrolled before the 2017 and 2018 influenza seasons in Peru and Thailand. Blood specimens were collected at enrollment and ≤14 days postpartum for testing by hemagglutination inhibition assay for antibodies against influenza reference viruses. Seroconversion was defined as a ≥4-fold rise in antibody titers from enrollment to postpartum with the second specimen's titer of ≥40. Throughout pregnancy, participants responded to twice weekly surveillance contacts asking about influenza vaccination and influenza-like symptoms (ILS). A mid-turbinate swab was collected with each ILS episode for influenza real-time reverse transcription polymerase chain reaction (rRT-PCR).

RESULTS

Of 1,466 participants without evidence of influenza vaccination during pregnancy, 296 (20.2%) had evidence of influenza virus infections. Fifteen (5.1%) were detected by rRT-PCR only, 250 (84.4%) by serologic testing only, and 31 (10.5%) by both methods.

CONCLUSIONS

Influenza virus infections during pregnancy occurred in 20% of cohort participants; >80% were not detected by a broad illness case definition coupled with rRT-PCR.

A deterministic model for homologous antibody dependant enhancement on influenza infection

Antibody dependant enhancement refers that viral infectivity was unexpectedly enhanced at low antibody concentration compared to when antibodies were absent, such as Dengue, Zika and influenza virus. To mathematically describe switch from enhancement to neutralisation with increase of antibody concentration, one hyperbolic tangent variant is used as switching function in existed models. However, switching function with hyperbolic tangent contains four parameters, and does not always increase with antibody concentration. To address this problem, we proposed a monotonically increasing Logistical function variant as switching function, which only contains position parameter and magnitude parameter. Analysing influenza viral titre estimated from 21 focus reduction assay (FRA) datasets from neutralisation group (viral titre lower than negative control on all serial dilutions) and 20 FRA dataset from enhancement group (viral titre higher than negative control on high serial dilution), switching function with Logistic function performs better than existed model independent of both groups and exhibited different behaviour/character; specifically, magnitude parameter estimated from enhancement group is lower, but position parameter estimated from enhancement group is higher. A lower magnitude parameter refers that enhancement group more rapidly switches from enhancement to neutralisation with increase of antibody concentration, and a higher position parameter indicates that enhancement group provides a larger antibody concentration interval corresponding to enhancement. Integrating estimated neutralisation kinetics with viral replication, we demonstrated that antibody-induced bistable influenza kinetics exist independent of both groups. However, comparing with neutralisation group, enhancement group provides higher threshold value of antibody concentration corresponding to influenza infectivity. This explains the observed phenomenon that antibody dependent enhancement enhances susceptibility, severity, and mortality to influenza infection. On population level, antibody dependant enhancement can promote H1N1 and H3N2 influenza virus cooperate to sustain long-term circulation on human populations according to antigenic seniority theory.

Codon optimized influenza H1 HA sequence but not CTLA-4 targeting of HA antigen to enhance the efficacy of DNA vaccines in an animal model

Infections caused by the influenza virus lead to both epidemic and pandemic outbreaks in humans and animals. Owing to their rapid production, safety, and stability, DNA vaccines represent a promising avenue for eliciting immunity and thwarting viral infections. While DNA vaccines have demonstrated substantial efficacy in murine models, their effectiveness in larger animals remains subdued. This limitation may be addressed by augmenting the immunogenicity of DNA-based vaccines. In the investigation here, protein expression was enhanced via codon optimization and then mouse cytotoxic T-lymphocyte antigen 4 (CTLA-4) was harnessed as a modulatory adjunct to bind directly to antigen-presenting cells. Further, the study evaluated the immunogenicity of two variants of the hemagglutinin (HA) antigen, i.e. the full-length and the C-terminal deletion versions. The study findings revealed that the codon-optimized HA gene (pcHA) led to increased protein synthesis, as evidenced by elevated mRNA levels. Codon optimization also significantly bolstered both cellular and humoral immune responses. In cytokine assays, all plasmid constructs, particularly pCTLA4-cHA, induced robust interferon (IFN)-γ production, while interleukin (IL)-4 levels remained uniformly non-significant. Mice immunized with pcHA displayed an augmented presence of IFNγ+ T-cells, underscoring the enhanced potency of the codon-optimized HA vaccine. Contrarily, CTLA-4-fused DNA vaccines did not significantly amplify the immune response.

Microparticle and nanoparticle-based influenza vaccines

Influenza infections are a health public problem worldwide every year with the potential to become the next pandemic. Vaccination is the most effective strategy to prevent future influenza outbreaks, however, influenza vaccines need to be reformulated each year to provide protection due to viral antigenic drift and shift. As more efficient influenza vaccines are needed, it is relevant to recapitulate strategies to improve the immunogenicity and broad reactivity of the current vaccines. Here, we review the current approved vaccines in the U.S. market and the platform used for their production. We discuss the different approaches to develop a broadly reactive vaccine as well as reviewing the adjuvant systems that are under study for being potentially included in future influenza vaccine formulations. The main components of the immune system involved in achieving a protective immune response are reviewed and how they participate in the trafficking of particles systemically and in the mucosa. Finally, we describe and classify, according to their physicochemical properties, some of the potential micro and nano-particulate platforms that can be used as delivery systems for parenteral and mucosal vaccinations.

Neuraminidase Antibody Response to Homologous and Drifted Influenza A Viruses After Immunization with Seasonal Influenza Vaccines

BACKGROUND/OBJECTIVES

Humoral immunity directed against neuraminidase (NA) of the influenza virus may soften the severity of infection caused by new antigenic variants of the influenza viruses. Evaluation of NA-inhibiting (NI) antibodies in combination with antibodies to hemagglutinin (HA) may enhance research on the antibody response to influenza vaccines.

METHODS

The study examined 64 pairs of serum samples from patients vaccinated with seasonal inactivated trivalent influenza vaccines (IIVs) in 2018 according to the formula recommended by the World Health Organization (WHO) for the 2018-2019 flu season. Antibodies against drift influenza viruses A/Guangdong-Maonan/SWL1536/2019(H1N1)pdm09 and A/Brisbane/34/2018(H3N2) were studied before vaccination and 21 days after vaccination. To assess NI antibodies, we used an enzyme-linked lectin assay (ELLA) with pairs of reassortant viruses A/H6N1 and A/H6N2. Anti-HA antibodies were detected using a hemagglutination inhibition (HI) test. The microneutralization (MN) test was performed in the MDCK cell line using viruses A/H6N1 and A/H6N2.

RESULTS

Seasonal IIVs induce a significant immune response of NI antibodies against influenza A/H1N1pdm09 and A/H3N2 viruses. A significantly reduced 'herd' immunity to drift influenza A/H1N1pdm09 and A/H3N2 viruses was shown, compared with previously circulating strains. This reduction was most pronounced in strains possessing neuraminidase N2. Seasonal IIVs caused an increase in antibodies against homologous and drifted viruses; however, an increase in antibodies to drifting viruses was observed more often among older patients. The level of NI antibodies for later A/H1N1pdm09 virus in response to IIVs was statistically significantly lower among younger people. After IIV vaccination, the percentage of individuals with HI antibody levels ≥ 1:40 and NI antibody levels ≥ 1:20 was 32.8% for drift A/H1N1pdm09 virus and 17.2% for drift A/H3N2 virus. Antisera containing HI and NI antibodies exhibited neutralizing properties in vitro against viruses with unrelated HA of the H6 subtype.

CONCLUSIONS

Drift A/H1N1pdm09 and A/H3N2 viruses demonstrated significantly lower reactivity to HI and NI antibodies against early influenza viruses. In response to seasonal IIVs, the level of seroprotection has increased, including against drift influenza A viruses, but protective antibody levels against A/H1N1pdm09 have risen to a greater extent. A reduced immune response to the N1 protein of the A/H1N1pdm09 drift virus was obtained in individuals under 60 years of age. Based on our findings, it is hypothesized that in the cases of a HA mismatch, vaccination against N1-containing influenza viruses may be necessary for individuals under 60, while broader population-level vaccination against N2-containing viruses may be required.

Modulation of B cell receptor activation by antibody competition

During repeated virus exposure, pre-existing antibodies can mask viral epitopes by competing with B cell receptors for antigen. Although this phenomenon has the potential to steer B cell responses away from conserved epitopes, the factors that influence epitope masking by competing antibodies remain unclear. Using engineered, influenza-reactive B cells, we investigate how antibodies influence the accessibility of epitopes on the viral surface. We find that membrane-proximal epitopes on influenza hemagglutinin are fundamentally at a disadvantage for B cell recognition because they can be blocked by both directly and indirectly competing antibodies. While many influenza-specific antibodies can inhibit B cell activation, the potency of masking depends on proximity of the targeted epitopes as well as antibody affinity, kinetics, and valency. Although most antibodies are inhibitory, we identify one that can enhance accessibility of hidden viral epitopes. Together, these findings establish rules for epitope masking that could help advance immunogen design.

Impact of Immunosenescence on Vaccine Immune Responses and Countermeasures

The biological progression of aging encompasses complex physiological processes. As individuals grow older, their physiological functions gradually decline, including compromised immune responses, leading to immunosenescence. Immunosenescence significantly elevates disease susceptibility and severity in older populations while concurrently compromising vaccine-induced immune responses. This comprehensive review aims to elucidate the implications of immunosenescence for vaccine-induced immunity and facilitate the development of optimized vaccination strategies for geriatric populations, with specific focus on COVID-19, influenza, pneumococcal, herpes zoster, and respiratory syncytial virus (RSV) vaccines. This review further elucidates the relationship between immunosenescence and vaccine-induced immunity. This review presents a systematic evaluation of intervention strategies designed to enhance vaccine responses in older populations, encompassing adjuvant utilization, antigen doses, vaccination frequency modification, inflammatory response modulation, and lifestyle interventions, including physical activity and nutritional modifications. These strategies are explored for their potential to improve current vaccine efficacy and inform the development of next-generation vaccines for geriatric populations.

H9 Consensus Hemagglutinin Subunit Vaccine with Adjuvants Induces Robust Mucosal and Systemic Immune Responses in Mice by Intranasal Administration

The H9N2 subtype avian influenza viruses mainly cause respiratory symptoms, reduce the egg production and fertility of poultry, and result in secondary infections, posing a great threat to the poultry industry and human health. Currently, all H9N2 avian influenza commercial vaccines are inactivated vaccines, which provide protection for immunized animals but cannot inhibit the spread of the virus and make it difficult to distinguish between the infected animals and vaccinated animals. In this study, a trimeric consensus H9 hemagglutinin (HA) subunit vaccine for the H9N2 subtype avian influenza virus based on a baculovirus expression system was first generated, and then the effects of three molecular adjuvants on the H9 HA subunit vaccine, Cholera toxin subunit B (CTB), flagellin, and granulocyte-macrophage colony-stimulating factor (GM-CSF) fused with H9 HA, and one synthetic compound, a polyinosinic-polycytidylic acid (PolyI:C) adjuvant, were evaluated in mice by intranasal administration. The results showed that these four adjuvants enhanced the immunogenicity of the H9 HA subunit vaccine for avian influenza viruses, and that GM-CSF and PolyI:C present better mucosal adjuvant activity for the H9 HA subunit vaccine. These results demonstrate that we have developed a potential universal H9 HA mucosal subunit vaccine with adjuvants in a baculovirus system that would be helpful for the prevention and control of H9N2 subtype avian influenza viruses.

Multi-strain modeling of influenza vaccine effectiveness in older adults and its dependence on antigenic distance

Influenza vaccine effectiveness (VE) varies seasonally due to host, virus and vaccine characteristics. To investigate how antigenic matching and dosage impact VE, we developed a mechanistic knowledge-based mathematical model. Immunization with a split vaccine is modeled for exposure to A/H1N1 or A/H3N2 virus strains. The model accounts for cross-reactivity of immune cells elicited during previous immunizations with new antigens. We simulated vaccine effectiveness (sVE) of high dose (HD) versus standard dose (SD) vaccines in the older population, from 2011 to 2022. We find that sVE is highly dependent on antigenic matching and that higher dosage improves immunogenicity, activation and memory formation of immune cells. In alignment with clinical observations, the HD vaccine performs better than the SD vaccine in all simulations, supporting the use of the HD vaccine in the older population. This model could be adapted to predict the impact of alternative virus strain selection on clinical outcomes in future influenza seasons.

mRNA vaccines for infectious diseases - advances, challenges and opportunities

The concept of mRNA-based vaccines emerged more than three decades ago. Groundbreaking discoveries and technological advancements over the past 20 years have resolved the major roadblocks that initially delayed application of this new vaccine modality. The rapid development of nucleoside-modified COVID-19 mRNA vaccines demonstrated that this immunization platform is easy to develop, has an acceptable safety profile and can be produced at a large scale. The flexibility and ease of antigen design have enabled mRNA vaccines to enter development for a wide range of viruses as well as for various bacteria and parasites. However, gaps in our knowledge limit the development of next-generation mRNA vaccines with increased potency and safety. A deeper understanding of the mechanisms of action of mRNA vaccines, application of novel technologies enabling rational antigen design, and innovative vaccine delivery strategies and vaccination regimens will likely yield potent novel vaccines against a wide range of pathogens.