Influenza antibody breadth and effector functions are immune correlates from acquisition of pandemic infection of children.

Cross-reactive antibodies with Fc receptor (FcR) effector functions may mitigate pandemic virus impact in the absence of neutralizing antibodies. In this exploratory study, we use serum from a randomized placebo-controlled trial of seasonal trivalent influenza vaccination in children (NCT00792051) conducted at the onset of the 2009 H1N1 pandemic (pH1N1) and monitored for infection. We found that seasonal vaccination increases pH1N1 specific antibodies and FcR effector functions. Furthermore, prospective baseline antibody profiles after seasonal vaccination, prior to pH1N1 infection, show that unvaccinated uninfected children have elevated ADCC effector function, FcγR3a and FcγR2a binding antibodies to multiple pH1N1 proteins, past seasonal and avian (H5, H7 and H9) strains. Whereas, children that became pH1N1 infected after seasonal vaccination have antibodies focussed to seasonal strains without FcR functions, and greater aggregated HA-specific profiles for IgM and IgG3. Modeling to predict infection susceptibility, ranked baseline hemagglutination antibody inhibition as the highest contributor to lack of pH1N1 infection, in combination with features that include pH1-IgG1, H1-stem responses and FcR binding to seasonal vaccine and pH1 proteins. Thus, seasonal vaccination can have benefits against pandemic influenza viruses, and some children already have broadly reactive antibodies with Fc potential without vaccination and may be considered 'elite influenza controllers'.

Superior antibody and membrane protein-specific T-cell responses to CoronaVac by intradermal versus intramuscular routes in adolescents.

BACKGROUND: Optimising the immunogenicity of COVID-19 vaccines to improve their protection against disease is necessary. Fractional dosing by intradermal (ID) administration has been shown to be equally immunogenic as intramuscular (IM) administration for several vaccines, but the immunogenicity of ID inactivated whole severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the full dose is unknown. This study (NCT04800133) investigated the superiority of antibody and T-cell responses of full-dose CoronaVac by ID over IM administration in adolescents. METHODS: Participants aged 11-17 years received two doses of IM or ID vaccine, followed by the 3rd dose 13-42 days later. Humoral and cellular immunogenicity outcomes were measured post-dose 2 (IM-CC versus ID-CC) and post-dose 3 (IM-CCC versus ID-CCC). Doses 2 and 3 were administered to 173 and 104 adolescents, respectively. RESULTS: Spike protein (S) immunoglobulin G (IgG), S-receptor-binding domain (RBD) IgG, S IgG Fcγ receptor IIIa (FcγRIIIa)-binding, SNM [sum of individual (S), nucleocapsid protein (N), and membrane protein (M) peptide pool]-specific interleukin-2 (IL-2)+CD4+, SNM-specific IL-2+CD8+, S-specific IL-2+CD8+, N-specific IL-2+CD4+, N-specific IL-2+CD8+ and M-specific IL-2+CD4+ responses fulfilled the superior and non-inferior criteria for ID-CC compared to IM-CC, whereas IgG avidity was inferior. For ID-CCC, S-RBD IgG, surrogate virus neutralisation test, 90% plaque reduction neutralisation titre (PRNT90), PRNT50, S IgG avidity, S IgG FcγRIIIa-binding, M-specific IL-2+CD4+, interferon-γ+CD8+ and IL-2+CD8+ responses were superior and non-inferior to IM-CCC. The estimated vaccine efficacies were 49%, 52%, 66% and 79% for IM-CC, ID-CC, IM-CCC and ID-CCC, respectively. The ID groups reported more local, mild adverse reactions. CONCLUSION: This is the first study to demonstrate superior antibody and M-specific T-cell responses by ID inactivated SARS-CoV-2 vaccination and serves as the basis for future research to improve the immunogenicity of inactivated vaccines.

Comparative antibody and cell-mediated immune responses, reactogenicity, and efficacy of homologous and heterologous boosting with CoronaVac and BNT162b2 (Cobovax): an open-label, randomised trial.

BACKGROUND: Few trials have compared homologous and heterologous third doses of COVID-19 vaccination with inactivated vaccines and mRNA vaccines. The aim of this study was to assess immune responses, safety, and efficacy against SARS-CoV-2 infection following homologous or heterologous third-dose COVID-19 vaccination with either one dose of CoronaVac (Sinovac Biotech; inactivated vaccine) or BNT162b2 (Fosun Pharma-BioNTech; mRNA vaccine). METHODS: This is an ongoing, randomised, allocation-concealed, open-label, comparator-controlled trial in adults aged 18 years or older enrolled from the community in Hong Kong, who had received two doses of CoronaVac or BNT162b2 at least 6 months earlier. Participants were randomly assigned, using a computer-generated sequence, in a 1:1 ratio with allocation concealment to receive a (third) dose of CoronaVac or BNT162b2 (ancestral virus strain), stratified by types of previous COVID-19 vaccination (homologous two doses of CoronaVac or BNT162b2). Participants were unmasked to group allocation after vaccination. The primary endpoint was serum neutralising antibodies against the ancestral virus at day 28 after vaccination in each group, measured as plaque reduction neutralisation test (PRNT50) geometric mean titre (GMT). Surrogate virus neutralisation test (sVNT) mean inhibition percentage and PRNT50 titres against omicron BA.1 and BA.2 subvariants were also measured. Secondary endpoints included geometric mean fold rise (GMFR) in antibody titres; incidence of solicited local and systemic adverse events; IFNγ+ CD4+ and IFNγ+ CD8+ T-cell responses at days 7 and 28; and incidence of COVID-19. Within-group comparisons of boost in immunogenicity from baseline and between-group comparisons were done according to intervention received (ie, per protocol) by paired and unpaired t test, respectively, and cumulative incidence of infection was compared using Kaplan-Meier curves and a proportional hazards model to estimate hazard ratio. The trial is registered with ClinicalTrials.gov, NCT05057169. FINDINGS: We enrolled participants from Nov 12, 2021, to Jan 27, 2022. We vaccinated 219 participants who previously received two doses of CoronaVac, including 101 randomly assigned to receive CoronaVac (CC-C) and 118 randomly assigned to receive BNT162b2 (CC-B) as their third dose; and 232 participants who previously received two doses of BNT162b2, including 118 randomly assigned to receive CoronaVac (BB-C) and 114 randomly assigned to receive BNT162b2 (BB-B) as their third dose. The PRNT50 GMTs on day 28 against ancestral virus were 109, 905, 92, and 816; against omicron BA.1 were 9, 75, 8, and 86; and against omicron BA.2 were 6, 80, 6, and 67 in the CC-C, CC-B, BB-C, and BB-B groups, respectively. Mean sVNT inhibition percentages on day 28 against ancestral virus were 83%, 96%, 87%, and 96%; against omicron BA.1 were 15%, 58%, 19%, and 69%; and against omicron BA.2 were 43%, 85%, 50%, and 90%, in the CC-C, CC-B, BB-C, and BB-B groups, respectively. Participants who had previously received two doses of CoronaVac and a BNT162b2 third dose had a GMFR of 12 (p<0·0001) compared with those who received a CoronaVac third dose; similarly, those who had received two doses of BNT162b2 and a BNT162b2 third dose had a GMFR of 8 (p<0·0001). No differences in CD4+ and CD8+ T-cell responses were observed between groups. We did not identify any vaccination-related hospitalisation within 1 month after vaccination. We identified 58 infections when omicron BA.2 was predominantly circulating, with cumulative incidence of 15·3% and 15·4% in the CC-C and CC-B groups, respectively (p=0·93), and 16·7% and 14·0% in the BB-C and BB-B groups, respectively (p=0·56). INTERPRETATION: Similar levels of incidence of, presumably, omicron BA.2 infections were observed in each group despite very weak antibody responses to BA.2 in the recipients of a CoronaVac third dose. Further research is warranted to identify appropriate correlates of protection for inactivated COVID-19 vaccines. FUNDING: Health and Medical Research Fund, Hong Kong. TRANSLATION: For the Chinese translation of the abstract see Supplementary Materials section.

Immunogenicity against wild-type and Omicron SARS-CoV-2 after a third dose of inactivated COVID-19 vaccine in healthy adolescents.

Introduction: Two doses of inactivated SARS-CoV-2 vaccine CoronaVac cannot elicit high efficacy against symptomatic COVID-19, especially against the Omicron variant, but that can be improved by a third dose in adults. The use of a third dose of CoronaVac in adolescents may be supported by immunobridging studies in the absence of efficacy data. Methods: With an immunobridging design, our study (NCT04800133) tested the non-inferiority of the binding and neutralizing antibodies and T cell responses induced by a third dose of CoronaVac in healthy adolescents (N=94, median age 14.2 years, 56% male) compared to adults (N=153, median age 48.1 years, 44% male). Responses against wild-type (WT) and BA.1 SARS-CoV-2 were compared in adolescents. Safety and reactogenicity were also monitored. Results: A homologous third dose of CoronaVac further enhanced antibody response in adolescents compared to just 2 doses. Adolescents mounted non-inferior antibody and T cell responses compared to adults. Although S IgG and neutralizing antibody responses to BA.1 were lower than to WT, they remained detectable in 96% and 86% of adolescents. T cell responses to peptide pools spanning only the mutations of BA.1 S, N and M in adolescents were preserved, increased, and halved compared to WT respectively. No safety concerns were identified. Discussion: The primary vaccination series of inactivated SARS-CoV-2 vaccines for adolescents should include 3 doses for improved humoral immunogenicity.

Antibody and T cell responses against wild-type and Omicron SARS-CoV-2 after third-dose BNT162b2 in adolescents.

The high effectiveness of the third dose of BNT162b2 in healthy adolescents against Omicron BA.1 has been reported in some studies, but immune responses conferring this protection are not yet elucidated. In this analysis, our study (NCT04800133) aims to evaluate the humoral and cellular responses against wild-type and Omicron (BA.1, BA.2 and/or BA.5) SARS-CoV-2 before and after a third dose of BNT162b2 in healthy adolescents. At 5 months after 2 doses, S IgG, S IgG Fc receptor-binding, and neutralising antibody responses waned significantly, yet neutralising antibodies remained detectable in all tested adolescents and S IgG avidity increased from 1 month after 2 doses. The antibody responses and S-specific IFN-γ+ and IL-2+ CD8+ T cell responses were significantly boosted in healthy adolescents after a homologous third dose of BNT162b2. Compared to adults, humoral responses for the third dose were non-inferior or superior in adolescents. The S-specific IFN-γ+ and IL-2+ CD4+ and CD8+ T cell responses in adolescents and adults were comparable or non-inferior. Interestingly, after 3 doses, adolescents had preserved S IgG, S IgG avidity, S IgG FcγRIIIa-binding, against Omicron BA.2, as well as preserved cellular responses against BA.1 S and moderate neutralisation levels against BA.1, BA.2 and BA.5. Sera from 100 and 96% of adolescents tested at 1 and 5 months after two doses could also neutralise BA.1. Our study found high antibody and T cell responses, including potent cross-variant reactivity, after three doses of BNT162b2 vaccine in adolescents in its current formulation, suggesting that current vaccines can be protective against symptomatic Omicron disease.

Immunogenicity and reactogenicity of SARS-CoV-2 vaccines BNT162b2 and CoronaVac in healthy adolescents.

We present an interim analysis of a registered clinical study (NCT04800133) to establish immunobridging with various antibody and cellular immunity markers and to compare the immunogenicity and reactogenicity of 2-dose BNT162b2 and CoronaVac in healthy adolescents as primary objectives. One-dose BNT162b2, recommended in some localities for risk reduction of myocarditis, is also assessed. Antibodies and T cell immune responses are non-inferior or similar in adolescents receiving 2 doses of BNT162b2 (BB, N = 116) and CoronaVac (CC, N = 123) versus adults after 2 doses of the same vaccine (BB, N = 147; CC, N = 141) but not in adolescents after 1-dose BNT162b2 (B, N = 116). CC induces SARS-CoV-2 N and N C-terminal domain seropositivity in a higher proportion of adolescents than adults. Adverse reactions are mostly mild for both vaccines and more frequent for BNT162b2. We find higher S, neutralising, avidity and Fc receptor-binding antibody responses in adolescents receiving BB than CC, and a similar induction of strong S-specific T cells by the 2 vaccines, in addition to N- and M-specific T cells induced by CoronaVac but not BNT162b2, possibly implying differential durability and cross-variant protection by BNT162b2 and CoronaVac, the 2 most used SARS-CoV-2 vaccines worldwide. Our results support the use of both vaccines in adolescents.

Comparison of the immunogenicity of BNT162b2 and CoronaVac COVID-19 vaccines in Hong Kong.

BACKGROUND AND OBJECTIVE: Few head-to-head evaluations of immune responses to different vaccines have been reported. METHODS: Surrogate virus neutralization test (sVNT) antibody levels of adults receiving either two doses of BNT162b2 (n = 366) or CoronaVac (n = 360) vaccines in Hong Kong were determined. An age-matched subgroup (BNT162b2 [n = 49] vs. CoronaVac [n = 49]) was tested for plaque reduction neutralization (PRNT) and spike-binding antibody and T-cell reactivity in peripheral blood mononuclear cells. RESULTS: One month after the second dose of vaccine, BNT162b2 elicited significantly higher PRNT50 , PRNT90 , sVNT, spike receptor binding, spike N-terminal domain binding, spike S2 domain binding, spike FcR binding and antibody avidity levels than CoronaVac. The geometric mean PRNT50 titres in those vaccinated with BNT162b2 and CoronaVac vaccines were 251.6 and 69.45, while PRNT90 titres were 98.91 and 16.57, respectively. All of those vaccinated with BNT162b2 and 45 (91.8%) of 49 vaccinated with CoronaVac achieved the 50% protection threshold for PRNT90. Allowing for an expected seven-fold waning of antibody titres over 6 months for those receiving CoronaVac, only 16.3% would meet the 50% protection threshold versus 79.6% of BNT162b2 vaccinees. Age was negatively correlated with PRNT90 antibody titres. Both vaccines induced SARS-CoV-2-specific CD4+ and CD8+ T-cell responses at 1 month post-vaccination but CoronaVac elicited significantly higher structural protein-specific CD4+ and CD8+ T-cell responses. CONCLUSION: Vaccination with BNT162b2 induces stronger humoral responses than CoronaVac. CoronaVac induces higher CD4+ and CD8+ T-cell responses to the structural protein than BNT162b2.

Universally Immune: How Infection Permissive Next Generation Influenza Vaccines May Affect Population Immunity and Viral Spread.

Next generation influenza vaccines that target conserved epitopes are becoming a clinical reality but still have challenges to overcome. Universal next generation vaccines are considered a vital tool to combat future pandemic viruses and have the potential to vastly improve long-term protection against seasonal influenza viruses. Key vaccine strategies include HA-stem and T cell activating vaccines; however, they could have unintended effects for virus adaptation as they recognise the virus after cell entry and do not directly block infection. This may lead to immune pressure on residual viruses. The potential for immune escape is already evident, for both the HA stem and T cell epitopes, and mosaic approaches for pre-emptive immune priming may be needed to circumvent key variants. Live attenuated influenza vaccines have not been immunogenic enough to boost T cells in adults with established prior immunity. Therefore, viral vectors or peptide approaches are key to harnessing T cell responses. A plethora of viral vector vaccines and routes of administration may be needed for next generation vaccine strategies that require repeated long-term administration to overcome vector immunity and increase our arsenal against diverse influenza viruses.

SARS-CoV-2 specific T cell responses are lower in children and increase with age and time after infection.

SARS-CoV-2 infection of children leads to a mild illness and the immunological differences with adults are unclear. Here, we report SARS-CoV-2 specific T cell responses in infected adults and children and find that the acute and memory CD4+ T cell responses to structural SARS-CoV-2 proteins increase with age, whereas CD8+ T cell responses increase with time post-infection. Infected children have lower CD4+ and CD8+ T cell responses to SARS-CoV-2 structural and ORF1ab proteins when compared with infected adults, comparable T cell polyfunctionality and reduced CD4+ T cell effector memory. Compared with adults, children have lower levels of antibodies to ß-coronaviruses, indicating differing baseline immunity. Total T follicular helper responses are increased, whilst monocyte numbers are reduced, indicating rapid adaptive co-ordination of the T and B cell responses and differing levels of inflammation. Therefore, reduced prior ß-coronavirus immunity and reduced T cell activation in children might drive milder COVID-19 pathogenesis.

SARS-CoV-2 specific T cell responses are lower in children and increase with age and time after infection.

SARS-CoV-2 infection of children leads to a mild illness and the immunological differences with adults remains unclear. We quantified the SARS-CoV-2 specific T cell responses in adults and children (<13 years of age) with RT-PCR confirmed asymptomatic and symptomatic infection for long-term memory, phenotype and polyfunctional cytokines. Acute and memory CD4+ T cell responses to structural SARS-CoV-2 proteins significantly increased with age, whilst CD8+ T cell responses increased with time post infection. Infected children had significantly lower CD4+ and CD8+ T cell responses to SARS-CoV-2 structural and ORF1ab proteins compared to infected adults. SARS-CoV-2-specific CD8+ T cell responses were comparable in magnitude to uninfected negative adult controls. In infected adults CD4+ T cell specificity was skewed towards structural peptides, whilst children had increased contribution of ORF1ab responses. This may reflect differing T cell compartmentalisation for antigen processing during antigen exposure or lower recruitment of memory populations. T cell polyfunctional cytokine production was comparable between children and adults, but children had a lower proportion of SARS-CoV-2 CD4+ T cell effector memory. Compared to adults, children had significantly lower levels of antibodies to ß-coronaviruses, indicating differing baseline immunity. Total T follicular helper responses was increased in children during acute infection indicating rapid co-ordination of the T and B cell responses. However total monocyte responses were reduced in children which may be reflective of differing levels of inflammation between children and adults. Therefore, reduced prior ß-coronavirus immunity and reduced activation and recruitment of de novo responses in children may drive milder COVID-19 pathogenesis.

Immunogenicity of standard, high-dose, MF59-adjuvanted, and recombinant-HA seasonal influenza vaccination in older adults.

The vaccine efficacy of standard-dose seasonal inactivated influenza vaccines (S-IIV) can be improved by the use of vaccines with higher antigen content or adjuvants. We conducted a randomized controlled trial in older adults to compare cellular and antibody responses of S-IIV versus enhanced vaccines (eIIV): MF59-adjuvanted (A-eIIV), high-dose (H-eIIV), and recombinant-hemagglutinin (HA) (R-eIIV). All vaccines induced comparable H3-HA-specific IgG and elevated antibody-dependent cellular cytotoxicity (ADCC) activity at day 30 post vaccination. H3-HA-specific ADCC responses were greatest following H-eIIV. Only A-eIIV increased H3-HA-IgG avidity, HA-stalk IgG and ADCC activity. eIIVs also increased polyfunctional CD4+ and CD8+ T cell responses, while cellular immune responses were skewed toward single-cytokine-producing T cells among S-IIV subjects. Our study provides further immunological evidence for the preferential use of eIIVs in older adults as each vaccine platform had an advantage over the standard-dose vaccine in terms of NK cell activation, HA-stalk antibodies, and T cell responses.

T Cells Targeting SARS-CoV-2: By Infection, Vaccination, and Against Future Variants.

T cell responses are a key cornerstone to viral immunity to drive high-quality antibody responses, establishing memory for recall and for viral clearance. Inefficient recruitment of T cell responses plays a role in the development of severe COVID-19 and is also represented by reduced cellular responses in men, children, and diversity compared with other epitope-specific subsets and available T cell receptor diversity. SARS-CoV-2-specific T cell responses are elicited by multiple vaccine formats and augmented by prior infection for hybrid immunity. Epitope conservation is relatively well-maintained leading to T cell crossreactivity for variants of concern that have diminished serological responses.

Author Correction: ORF8 and ORF3b antibodies are accurate serological markers of early and late SARS-CoV-2 infection.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

ORF8 and ORF3b antibodies are accurate serological markers of early and late SARS-CoV-2 infection.

The SARS-CoV-2 virus emerged in December 2019 and has caused a worldwide pandemic due to the lack of any pre-existing immunity. Accurate serology testing is urgently needed to help diagnose infection, determine past exposure of populations and assess the response to a future vaccine. The landscape of antibody responses to SARS-CoV-2 is unknown. In this study, we utilized the luciferase immunoprecipitation system to assess the antibody responses to 15 different SARS-CoV-2 antigens in patients with COVID-19. We identified new targets of the immune response to SARS-CoV-2 and show that nucleocapsid, open reading frame (ORF)8 and ORF3b elicit the strongest specific antibody responses. ORF8 and ORF3b antibodies, taken together as a cluster of points, identified 96.5% of COVID-19 samples at early and late time points of disease with 99.5% specificity. Our findings could be used to develop second-generation diagnostic tests to improve serological assays for COVID-19 and are important in understanding pathogenicity.

Assessment of enhanced influenza vaccination finds that FluAd conveys an advantage in mice and older adults.

OBJECTIVES: Enhanced inactivated influenza vaccines (eIIV) aim to increase immunogenicity and protection compared with the widely used standard IIV (S-IIV). METHODS: We tested four vaccines in parallel, FluZone high dose, FluBlok and FluAd versus S-IIV in a randomised controlled trial of older adults and in a mouse infection model to assess immunogenicity, protection from lethal challenge and mechanisms of action. RESULTS: In older adults, FluAd vaccination stimulated a superior antibody profile, including H3-HA antibodies that were elevated for up to 1 year after vaccination, higher avidity H3HA IgG and larger HA stem IgG responses. In a mouse model, FluAd also elicited an earlier and larger induction of HA stem antibodies with increased germinal centre responses and upregulation and long-term expression of B-cell switch transcription factors. Long-term cross-reactive memory responses were sustained by FluAd following lethal heterosubtypic influenza challenge, with reduced lung damage and viral loads, coinciding with increased T- and B-cell recall. Advantages were also noted for the high-dose FluZone vaccine in both humans and mice. CONCLUSION: The early, broadly reactive and long-lived antibody response of FluAd indicates a potential advantage of this vaccine, particularly in years when there is a mismatch between the vaccine strain and the circulating strain of influenza viruses.