ETIDIOH - NEW

  Abstract Influenza continues to cause significant mortality globally and possesses substantial pandemic potential . Assessing pandemic risk requires a clear understanding of existing population immunity . Leveraging a unique large-scale cohort of human sera , we evaluated total and neutralising antibody -mediated immunity to multiple haemagglutinin (HA) proteins, including those from subtypes with high pandemic potential. Our analysis reveals that population immunity is heterogeneous , with distinct age-dependent differences in responses to H5, H7, and H9 avian influenza subtypes. These shifts align with historical circulation patterns of seasonal H1N1 and H3N2 human viruses. Notably, H7 viruses are primarily neutralised through head domain epitopes , while H5 viruses are targeted mainly via stem epitopes , although in both instances some neutralisation occurred via receptor binding site-adjacent epitopes . Furthermore, H7 responses were dominated by non-glycan-targeted IgG2 anti...

  Abstract H5N1 highly pathogenic avian influenza viruses have spread globally and pose a risk for a human pandemic . Prior studies suggest that early life exposures to group 1 influenza viruses (H1N1 and H2N2) prime antibodies that cross-react to the hemagglutinin of H5N1 , which is also a group 1 virus. Less is known about how immune history affects antibody responses against the neuraminidase (NA) of H5N1 viruses. Here, we measured NA inhibition antibodies against multiple H5N1 viruses using sera from 155 individuals born between 1927 and 2016 . We found that individuals primed in childhood with H1N1 viruses were more likely to possess higher levels of antibodies that cross-react with the NA of H5N1 viruses compared to individuals primed in childhood with H2N2 or H3N2 viruses. While young children rarely possessed cross-reactive NA antibodies, we found that childhood infections with contemporary H1N1 , but not H3N2, viruses can elicit them. These data suggest that immune history...

  Abstract As intrinsic differences in humoral immune response to SARS-CoV-2 between children and adults remain unclear , we improved characterisation by defining the kinetics, specificity and function of antibodies to SARS-CoV-2 in children (n = 146, aged 9.4 ± 4.8 years with n = 257 samples) compared to adults (n = 85, aged 39.5 ± 15.2 years with n = 122 samples). We used plasma samples from an infection and vaccination-naive cohort study with RT-PCR confirmed ancestral B.1* SARS-CoV-2 virus infection with asymptomatic or mild disease, collected in Hong Kong between March to December 2020, from acute (0–14 days post infection) to convalescent (15–206 days) timepoints. Children had significantly lower primary antibody responses against SARS-CoV-2 proteins overall, leading to a less isotype switched response. While children had lower OC43 Spike and SARS-CoV-2 S2 IgG and avidity than adults, they exhibited higher avidities for SARS-CoV-2 whole Spike and Nucleocapsid , and higher lev...

  Abstract Reassortment between different influenza strains occurs when they co-infect the same host cell . The emergence of a reassortant virus depends on both its intrinsic fitness and extrinsic factors , including pre-existing humoral immunity . The generation of pandemic strains , such as H2N2 and H3N2 , and zoonotic influenza A viruses, like H5N6, H5N8, and H7N9 , in birds is suggested to be the result of extensive selection by pre-existing antibodies . To further explore the role of humoral immunity in reassortment , we generated two divergent fluorescent protein-expressing viruses and used strain-specific and cross-reactive monoclonal antibodies (mAbs) to assess the impact of cross-immunity on reassortment. Our results indicate that all mAbs altered the genotypic diversity and significantly reduced the release of progeny virions in co-infected cells both in vitro and in vivo. Moreover, antibody transfer studies in mice revealed protection from challenge with divergent pathog...

ABSTRACT Seasonal influenza causes 290,000–650,000 deaths annually, with vaccination efficacy ranging from 10 to 60%. The emergence of drug-resistant and highly pathogenic avian influenza viruses underscores the urgent need for novel protective strategies . Epidemiological observations have long suggested that certain vaccines, such as Bacillus Calmette-Guérin (BCG), can provide protection against diverse pathogens (S. Biering-Sørensen, P. Aaby, N. Lund, et al., Clin Infect Dis 65:1183–1190, 2017, https://doi.org/10.1093/cid/cix525 ; M.-L. Garly, C. L. Martins, C. Balé, et al., Vaccine 21:2782–2790, 2003, https://doi.org/10.1016/s0264-410x(03)00181-6 ; C. A. G. Timmermann, S. Biering‐Sørensen, P. Aaby, et al., Trop Med Int Health 20:1733–1744, 2015, https://doi.org/10.1111/tmi.12614 ). While the cellular and molecular mechanisms underlying such protection remain incompletely understood, emerging research offers critical insights into innate immune system modulation (B. Cirovic, L. C. J...

Abstract Background .  Highly pathogenic avian influenza A(H5) viruses pose a pandemic threat , with a history of zoonotic spillovers into humans that are presumed immunologically naive. Whether the general population is currently immunologically naive to circulating A(H5) influenza viruses is unknown.  Methods .  To evaluate the presence of cross-reactive immune responses to emerging A(H5) clade 2.3.4.4b influenza viruses in the general population, we conducted comprehensive immune profiling on cross-sectional samples from healthcare workers (n=107). Samples were collected in August and September 2024 in the scope of an ongoing prospective follow-up study: Surveillance of rEspiratory viruses iN healThcare and anImal workers in the NethErLands (SENTINEL).  Findings .  Low-level antibody responses directed against the A(H5) hemagglutinin (HA) head were detected in a limited number of individuals , but without hemagglutination inhibition activity. Nevertheless, we...

Editor’s summary The vast majority of the human population has immunity to influenza A virus (IAV) by prior infection, vaccination, or both . However, protection is generally subtype-specific , and it is not clear whether prior infection against one subtype could confer protection against clade 2.3.4.4b H5N1 IAVs , which are currently circulating in birds and dairy cows . Here, Restori et al. demonstrated that prior infection with the 2009 pandemic H1N1 IAV was protective against subsequent direct infection with H5N1 IAV in ferrets. Moreover, prior immunity reduced susceptibility to infection by transmission from an infected donor ferret. These data suggest that prior immunity to IAV, especially to the 2009 pandemic H1N1 virus, may offer a degree of protection against H5N1 infection. —Courtney Malo Abstract Zoonotic infections with emerging influenza viruses occur in the context of population-wide immunity to seasonal strains . Because of the worldwide spread of highly pathogenic clade...

Abstract The spill-over of Influenza A virus H5N1 clade 2.3.4.4b from cattle to humans highlights the risk of a human H5N1 pandemic . Given the impact of pre-existing immunity on the course and severity of viral infections, we comprehensively assessed the humoral immunity against the H5N1 A/Texas/37/2024 isolate in H5N1- naive individuals . To this end, we performed complementary binding and neutralization assays on 66 subjects and ranked activities among a panel of 76 influenza A virus isolates. We detected low but distinct cross-neutralizing titers against A/Texas/37/2024 with a 3.9 to 15.6-fold reduction compared to selected H1N1 or H3N2 strains. By cloning and evaluating 136 monoclonal antibodies from memory B cells, we identified potent A/Texas/37/2024-neutralizing monoclonal antibodies in five out of six investigated individuals. These antibodies cross-neutralize H1, compete with antibodies targeting the HA stem, and protect mice from lethal H5N1 challenge. Our findings demonstra...

Abstract An increase in the number of human cases of influenza A/H5N1 infection in the US has raised concerns about the pandemic potential of the virus . Preexisting population immunity is a key determinant for risk assessment and pandemic potential for any virus. Antibody responses against the bovine A/H5N1 hemagglutinin (HA) and neuraminidase (NA) proteins were measured among a population of influenza-vaccinated or influenza-infected individuals . Modest titers of bovine A/H5N1 HA-binding antibodies and low to undetectable neutralizing antibody responses were detected in a cohort of 73 individuals . Conversely, bovine A/H5N1 NA binding and neuraminidase-inhibiting antibody responses were comparable to those against a human A/ H1N1 NA at baseline. Seasonal influenza vaccination failed to significantly increase antibody titers against both HA and NA glycoproteins of bovine A/H5N1. Recent infection with human A/H1N1 but not A/H3N2 viruses induced significant increases in bovine A/H5N1 n...

Abstract Highly pathogenic avian influenza of the H5N1 subtype has shown recent unprecedented expansion in its geographic and host range , increasing the pandemic threat . The younger age of H5N1 versus H7N9 avian influenza in humans has previously been attributed to imprinted pre-immunity to hemagglutinin stalk (HA2) epitopes shared with group 1 ( H1N1, H2N2 ) versus group 2 ( H3N2 ) influenza A subtypes predominating in the human population before versus after 1968, respectively. Here we review the complex immuno-epidemiological interactions underpinning influenza risk assessment and extend the imprinting hypothesis to include a potential role for cross-protective neuraminidase (NA) imprinting . We compare H5N1 distributions and case fatality ratios by age and birth cohort (as proxy for HA2 and/or NA imprinting epoch) not only to H7N9 but also H5N6 and H9N2 avian influenza, representing more varied conditions of zoonotic influenza relatedness to human subtypes of the past century. We...

Abstract Avian H15 influenza viruses are closely related to H7 viruses, but feature a unique 9-amino acid insertion in their hemagglutinin head domain , creating an additional site for antigenic variation . Here, we characterized a panel of mouse monoclonal antibodies (mAbs) raised against the A/wedge-tailed shearwater/Western Australia/2576/1979 ancestral strain , and a human mAb isolated from an H7N9 vaccinee . We found differences in binding and neutralization profiles against the ancestral strain and drifted strains of H15 isolated after 2008. MAbs that have hemagglutination inhibition activity against the ancestral strain do not show binding to drifted strains , hinting at antigenic differences in the receptor binding site . We show that the mAbs protect in vivo and elucidate mAb-antigen interactions using negative stain and cryo-electron microscopy. The characterization of H15 antigenicity and mechanisms of antibody-mediated neutralization expands our knowledge of this rare avian...

Abstract The ongoing spread of highly pathogenic avian influenza H5N1 clade 2.3.4.4b virus in animals and occasional spillover to humans have raised concerns about a potential H5N1 pandemic. Although recent studies have shown that pre-existing human antibodies can recognize H5N1 neuraminidase , there is a lack of molecular understanding of how this cross-reactivity develops. Using a phage display antibody library derived from 245 healthy donors , this study isolates an antibody, known as HB420 , that cross-reacts with the neuraminidases of human H3N2 and avian H5N1 clade 2.3.4.4b viruses and confers protection in vivo. Cryo-EM analysis shows that HB420 targets the neuraminidase active site by mimicking sialic acid binding through a single Asp residue. Additionally, the inferred germline of HB420 is N2-specific but acquires cross-reactivity to H5N1 neuraminidase through somatic hypermutations . Overall, our findings provide insights into how neuraminidase antibody evolves breadth, which...

Abstract Introduction Middle East respiratory syndrome (MERS) is a zoonotic viral respiratory disease caused by the Middle East respiratory syndrome coronavirus (MERS-CoV), associated with severe clinical outcomes and high mortality. Objectives Our study examined the kinetics of anti-MERS-CoV IgM and IgG antibodies during the acute and convalescent phases of infection, focusing on their correlations with clinical variables such as age and viral load. Methods Serum samples were collected from PCR-confirmed MERS-CoV patients (n = 23) during both phases and compared to healthy controls (n = 23) using validated ELISA-based assays. Results IgM levels peaked in the acute phase and declined significantly in the convalescent phase , while IgG levels were sustained and markedly higher during recovery . Correlation analyses revealed positive relationships between antibody levels and patient age (acute IgM: r = 0.56, p < 0.01; convalescent IgG: r = 0.59, p < 0.01) and viral loads (acute IgM...

Abstract Frequent SARS-CoV-2 vaccination in vulnerable populations has raised concerns that this may contribute to T cell exhaustion , which could negatively affect the quality of immune protection. Herein, we examined the impact of repeated SARS-CoV-2 vaccination on T cell phenotypic and functional exhaustion in frail older adults in long-term care (n = 23), individuals on immunosuppressive drugs (n = 10), and healthy adults (n = 43), in Canada . Spike-specific CD4+ and CD8+ T cell levels did not decline in any cohort following repeated SARS-CoV-2 vaccination, nor did the expression of exhaustion markers on spike-specific or total T cells increase. T cell production of multiple cytokines (i.e. polyfunctionality) in response to the spike protein of SARS-CoV-2 did not decline in any cohort following repeated vaccination. None of the cohorts displayed elevated levels of terminally differentiated T cells following multiple SARS-CoV-2 vaccinations. Thus, repeated SARS-CoV-2 vaccination was...

Highlights •  Different immune responses in mice vaccinated with influenza A(H5N1) than with other subtypes. •  Highly pathogenic avian influenza A(H5N1)-vaccinated mice had altered germinal center responses. •  A(H5N1)-vaccinated mice had fewer dLN germinal centers and more extrafollicular B cells. •  A(H5N1)-vaccinated mice had more dLN follicular helper and regulatory T cells. •  Our study represents a timely assessment of A(H5N1) risk to human health. Abstract Highly pathogenic avian influenza (HPAI) H5N1 virus vaccines typically yield lower neutralizing antibody titers in animals than influenza A virus (IAV) vaccines derived from other viral subtypes. To understand these differences, we compared the cellular immune responses in the draining lymph nodes (dLNs) of mice vaccinated with an inactivated whole H5N1 vaccine to those in mice vaccinated with seasonal H1N1pdm09, H7N9, or H9N2 IAV vaccines . H5N1-vaccinated mice exhibited reduced serum neutralizing ant...

ABSTRACT Recent documented infection with an endemic coronavirus (eCoV) is associated with less severe coronavirus disease 2019 (COVID-19), yet the immune mechanism behind this protection has not been fully explored. We measured both antibody and T-cell responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in SARS-CoV-2- naïve individuals , classified into two groups: those with or without presumed recent eCoV infections . There was no difference in neutralizing antibodies and T-cell responses against SARS-CoV-2 antigens between the two groups. SARS-CoV-2-naïve individuals with recent presumed eCoV infection, however, had higher and significantly correlated levels of Fc receptor (FcR)-binding antibodies against eCoV spikes (S) and SARS-CoV-2 S2. Recent eCoV infection boosts cross-reactive antibodies that can mediate Fc effector functions, and this may play a role in the observed heterotypic immune protection against severe COVID-19. IMPORTANCE With the recent e...

Abstract Infections by influenza A virus (IAV) are a significant cause of global mortality . The pathogenesis of the infection is usually studied in terms of direct viral-induced damage or the overreactive immune response that continues after the virus is cleared. However, factors such as the initial infectious dose , the early response after infection in different cell types, and the presence of autoantibodies for relevant antiviral cytokines like type I IFNs seem to influence the course of the infection and lead to fatal outcomes . In this article, we address the current knowledge about the early events during influenza virus infection, which are important for their participation in influenza-derived pathogenesis. Source: Viruses,  https://www.mdpi.com/1999-4915/17/5/694 ____

Abstract Recent influenza vaccine formulations have improved the magnitude of B-cell antibody responses in older adults ; however, older adults remain significantly at risk for severe influenza-related illness . Although antibodies are an important metric of vaccine effectiveness, they only represent one aspect of the immune response. In this study, we combined in vitro and ex vivo assays with human samples to investigate B, CD4+ T, and myeloid cell responses to influenza vaccine antigens . We found that older adults mounted equivalent antibody titers to younger adults but had fewer influenza-specific CD4+ T cells and reduced antiviral-associated T helper cell populations. Single-cell transcriptomics revealed that older adults had attenuated interferon transcriptional signatures in T helper and myeloid cell subsets . These data suggest that with aging, transcriptional programming alterations in myeloid cells contribute to reduced antiviral T cell responses, and formulating vaccines tai...

Abstract Immunisation remains the most cost-effective mechanism to combat global influenza infection and is widely employed against seasonal influenza viruses. Zoonotic transmission of avian influenza A viruses represents a significant threat to human health given the lack of population level immunity , which could translate into an influenza pandemic . Therefore, there is a need to better understand pre-existing human immunity against avian influenza strains. as highlighted by the recent rapid, global spread of avian H5Nx clade 2.3.4.4b variants. Here, we sought to quantify the frequencies and specificities of B cells recognising avian hemagglutinin (HA) within unexposed adults , and to characterise the ability of seasonal immunisation to boost cross-reactive immune responses to H5Nx strains, including from clade 2.3.4.4b. Low but detectable serum antibody titres against H5 and H7 avian influenza HA were observed in donors. The frequency of memory B cells with cross-reactive recogniti...

Abstract The unprecedented 2.3.4.4b A(H5N1) outbreak in dairy cattle, poultry, and spillover to humans in the United States (US) poses a major public health threat . Population immunity is a critical component of influenza pandemic risk assessment. We conducted a comprehensive assessment of the population immunity to 2.3.4.4b A(H5N1) viruses and analyzed 1794 sera from 723 people (0.5-88 yrs) in multiple US geographic regions during 2021-2024. Low pre-existing neutralizing and hemagglutinin (HA) head binding antibodies and substantial cross reactive binding antibodies to N1 neuraminidase (NA) of 2.3.4.4b A(H5N1) were detected in US population. Antibodies to group 1 HA stalk were also prevalent with an age-related pattern. A( H1N1 )pdm09 infection and influenza vaccination did not induce neutralizing antibodies but induced significant rise of NA inhibition (NAI) antibodies to N1 of 2.3.4.4b A(H5N1), and group 1 HA stalk antibodies. Understanding population susceptibility to novel influe...