Search Results (993)

Background/Objectives: Waning immunity after primary COVID-19 vaccination supports evaluation of additional doses. HXP-GPOVac is an egg-based, inactivated Newcastle disease virus (NDV)-vectored vaccine expressing a prefusion-stabilized SARS-CoV-2 HexaPro spike antigen. We evaluated the safety, tolerability, and immunogenicity of a single additional 10 µg dose of HXP-GPOVac administered to adults previously primed with two doses of either HXP-GPOVac or BNT162b2. Methods: Study GPO NDV-HXP-S 203 was an open-label phase II extension enrolling adults (18–75 years) who previously completed a two-dose primary series in Study 202 with either HXP-GPOVac or BNT162b2 (Pfizer–BioNTech; Comirnaty). All participants received a single additional 10 µg intramuscular dose of HXP-GPOVac ≥ 6 months after their second primary dose. Solicited local/systemic adverse events (AEs) were recorded for 7 days, unsolicited AEs through Day 28, and serious AEs (SAEs) and adverse events of special interest (AESIs) throughout follow-up. Neutralizing antibody titers (pseudovirus 50% neutralization titer, NT₅₀) and anti-spike IgG (BAU/mL) were assessed pre-dose (Day 1) and post-vaccination through 12 months; a predefined subset underwent IFN-γ and IL-5 ELISpot. SARS-CoV-2 infection during follow-up was assessed using anti-nucleocapsid (anti-N) IgG. Symptomatic COVID-19 was identified through symptom-reported, symptom-triggered RT-PCR testing; sequencing was performed when feasible. Results: All 219 participants received HXP-GPOVac (167 primed with HXP-GPOVac and 52 with BNT162b2). Any solicited local reaction occurred in 22.2% (37/167) of HXP-GPOVac-primed and 26.9% (14/52) of BNT162b2-primed participants; any solicited systemic reaction occurred in 10.8% (18/167) and 13.5% (7/52), respectively. No vaccine-related unsolicited AEs or AESIs were reported. Three deaths occurred during the 12-month follow-up; one (a sudden cardiac death in an HXP-GPOVac-primed participant) was assessed by the safety medical team as possibly related to vaccination, and two were assessed as not related. Neutralizing antibody GMTs increased from 46.33 at baseline to 1569.04 at Day 15 in HXP-GPOVac-primed participants and from 77.25 to 841.34 in BNT162b2-primed participants; corresponding SCRs were 78.8% and 76.9%. Anti-spike IgG GMCs increased from 48.79 to 1480.14 BAU/mL and from 194.48 to 1547.88 BAU/mL, respectively. Responses declined over time but remained above baseline through 12 months. In the cellular immunity subset, post-vaccination IFN-γ responses increased, with comparatively modest IL-5 responses and no pattern suggestive of Th2 predominance. Conclusions: A single additional dose of HXP-GPOVac administered ≥6 months after primary vaccination with HXP-GPOVac or BNT162b2 was generally well tolerated and elicited robust recall humoral responses, with supportive findings of cellular immunity. Trial registration: Thai Clinical Trials Registry, TCTR20230213001. Full article

Identifying antigens that elicit protective immunity is the key step for vaccine development. Here, we describe the use of the MS2 VLP platform to identify epitopes of SARS-CoV-2 structural proteins recognized by antibodies from COVID-19 patients, and to present those epitopes to the immune system as vaccines. We constructed an MS2 virus-like particle (VLP) library covering all four structural proteins of SARS-CoV-2 and affinity-selected vaccine candidates by biopanning on antibodies from infected humans. We focused on the structural proteins, reasoning that they are the most likely targets of a protective antibody response. The epitopes we found map almost entirely to the spike and nucleocapsid proteins. The VLPs displaying such epitopes were produced individually in E. coli and then tested for their potential as vaccines. While none of the affinity-selected spike-specific VLPs elicited neutralizing antibodies, VLPs displaying nucleocapsid epitopes induced protective immunity in a hamster model. This work illustrates the MS2 VLP platform’s capacity for the identification of new vaccine candidates and raises the possibility that VLPs displaying nucleocapsid epitopes could provide long-lasting protection against a range of virus variants. Full article

Background: The COVID-19 pandemic exposed critical gaps in pandemic preparedness and highlighted the need for vaccine platforms capable of rapid adaptation. Outer membrane vesicle (OMV)-based platforms utilizing vesicles derived from genetically detoxified Neisseria meningitidis serogroup B (Nm-nOMV) represent a promising plug-and-play approach. Methods: This Phase I, first-in-human, randomized, double-blind, placebo- and OMV-controlled trial, evaluated safety, tolerability, and immunogenicity of intranasally administered OMVs combined with SARS-CoV-2 Spike protein in healthy SARS-CoV-2 seropositive adults aged 18–55 years. Forty participants were enrolled across two cohorts: a low-dose cohort receiving 140 μg OMV/70 μg Spike (OMV + Spike, n = 13; OMV alone, n= 3; Placebo, n = 5) and a high-dose cohort receiving 280 μg of OMV/140 μg of Spike (OMV + Spike, n = 13; OMV alone, n = 3; Placebo, n = 3), administered on Days 1 and 22. Safety was assessed through adverse events, vital signs, laboratory parameters, ECG, and pulse oximetry. Immunogenicity was evaluated via systemic SARS-CoV-2 neutralizing antibodies, antigen-specific antibodies (IgG and IgA), and mucosal antibodies (IgA in nasal wash). Results: Intranasal administration of OMVs combined with SARS-CoV-2 Spike protein was safe, well-tolerated, and immunogenic. No serious adverse events were reported, and adverse events were predominantly mild and transient. Dose-dependent increases in systemic and mucosal immune responses were observed, with statistically significant enhanced serum IgG and nasal wash IgA antibodies in the high-dose group. Conclusions: The current clinical data confirm key aspects of the preclinical profile, which demonstrate the potential of the Nm-nOMV platform as a strong adjuvant for mucosal vaccines. These findings support the broader application of the Nm-nOMV vaccine platform in pandemic preparedness. Full article

Background: While vaccines are designed to elicit targeted immune responses, in some cases, the immunogenic molecules employed can inherently interact with broader host cellular pathways as a secondary consequence. This phenomenon can be exemplified by COVID-19 vaccines. COVID-19 vaccines, including mRNA platforms, use the SARS-CoV-2 spike protein as an immunogen to induce the production of neutralizing antibodies. The spike protein binds the ACE2 (angiotensin-converting enzyme 2) receptor on human cells, mediating viral entry and infection. ACE2 is widely expressed across multiple tissues and is a key component of the renin–angiotensin–aldosterone system (RAAS) that acts as a homeostatic regulator of systemic and local blood flow, blood pressure, cardiac function, fluid balance and immunity. Some studies have proposed the interaction between the spike protein and ACE2 as a possible contributing factor to rare adverse effects observed following COVID-19 vaccination, including myocarditis, pericarditis, thrombosis, and reported alterations in blood pressure, though these mechanisms remain to be fully elucidated. Objectives: As a proof-of-concept approach in vaccine antigen development, we engineered SARS-CoV-2 spike mutants with impaired binding to the host receptor ACE2. Methods: By rational design, we produced and validated in vitro and in vivo spike point mutants that do not effectively bind ACE2. Results: The engineered spike mutants do not effectively bind the human entry receptor ACE2 while retaining the immunogenic properties equal to or better than the wild type spike and thus generate a protective response in animals when used as a vaccination agent. Conclusions: By establishing a straightforward molecular strategy for rational vaccine design, this work demonstrates the feasibility of limiting specific antigen–host receptor interactions while maintaining immunogenicity. This approach may be applicable to future vaccination strategies where antigen interaction with host cells could potentially interfere with physiological pathways. Full article

Neutralizing antibodies (NABs) play a critical role in assessing the immune response elicited by vaccines, providing insight into their protective efficacy. Despite their importance, there is a notable gap in research directly comparing NAB levels among individuals vaccinated with different vaccines, across diverse ethnicities, and between genders. The study aimed to compare NAB levels across variables such as vaccination status, vaccine type, age, gender, and ethnicity. The NAB levels among different study groups were measured using the Finecare RBD Antibody Test and the cPass kit (ELISA). The data was analyzed statistically using SPSS version 27. A total of 172 study subjects were analyzed. The mean age of participants was 45.03 ± 16.72 years, with 50.9% male and 77.3% of Malay ethnicity. Median NAB levels, assessed by both assays, were highest in females, vaccinated healthy participants, and those who received the Pfizer vaccine. Age-group comparisons revealed variations in median NAB levels across studied groups. Participants aged 10–25 years in the vaccinated healthy (VH) group exhibited the highest median antibody levels; on the other hand, the 26–45 year age group showed the highest median levels in the breakthrough infection (BI) and certain non-vaccinated categories. Ethnic group comparisons highlighted that Malays consistently had the highest median NAB levels. Significant differences in antibody levels were found across vaccination status, ethnicity, and vaccine type (p < 0.001). This study underscores the influence of vaccination status, demographic factors, and vaccine type on NAB levels. The Finecare RBD Antibody Test and cPass kit demonstrated comparable trends, highlighting their utility in evaluating vaccine-induced immunity. The findings of this study highlight the need for tailored immunization strategies to optimize protective immunity. Full article

Background: Monoclonal antibodies (mAbs) initially played a major role in outpatient COVID-19 management by providing rapid passive immunity and reducing progression to severe disease. However, continuous SARS-CoV-2 evolution progressively compromised the effectiveness of several anti-spike products. This narrative review summarizes the trajectory of COVID-19 mAbs across three phases: early clinical efficacy, loss of efficacy due to immune escape, and future directions. Methods: We conducted a narrative review focusing on mechanisms of action, pivotal clinical trials, and real-world effectiveness of neutralizing anti-spike mAbs and host-directed immunomodulatory mAbs. Emphasis was placed on the impact of variants—especially Omicron—on susceptibility and clinical use, as well as on emerging next-generation platforms. Results: First-generation neutralizing mAbs substantially reduced the hospitalization rates during the Alpha and Delta waves, while immunomodulatory mAbs became standard options for the hyperinflammatory phase in hospitalized patients. With the emergence of Omicron and its sub-lineages, extensive immune escape led to marked reductions in neutralization for many earlier anti-spike agents and consequent restrictions in use. Later-generation approaches targeting more conserved epitopes provided temporary solutions but were also challenged by ongoing antigenic drift. Host-directed immunomodulators retained clinical relevance because their mechanism is independent of viral spike mutations. Conclusions: The clinical role of monoclonal antibodies in COVID-19 has been dynamic and increasingly constrained by viral evolution. Future strategies should prioritize broadly neutralizing antibodies targeting conserved epitopes, innovative delivery platforms, and integration with real-time surveillance to preserve clinical utility in the endemic phase and improve preparedness for future outbreaks. Full article

Background/Objectives: In the first months of their life, infants rely on maternal antibodies for immune protection. Breastmilk is a major source of these defenses, supplying secretory IgA, IgG, and IgM that help guard mucosal surfaces against pathogens such as SARS-CoV-2. Most studies on breastmilk immunity in the context of COVID-19 have emphasized circulating monomeric IgA, rather than the multimeric secretory IgA (sIgA) that is active at mucosal barriers. This study assessed in-depth the contribution of breastmilk antibody subtypes to SARS-CoV-2 neutralization capacity and how these profiles differ following maternal COVID-19 infection versus vaccination during pregnancy or postpartum. Methods: In this prospective cohort study, breastmilk samples were collected longitudinally from individuals who had COVID-19 during pregnancy or received COVID-19 mRNA vaccination during pregnancy or postpartum. Serological assays measured IgG, IgM, systemic IgA, and secretory IgA against SARS-CoV-2 spike and nucleocapsid antigens. Results: COVID-19 infection during pregnancy resulted in significantly higher systemic and secretory IgA levels compared to vaccination. Secretory IgA demonstrated a strong correlation with neutralization capacity. Principal component analysis revealed distinct antibody profiles in COVID-19-exposed individuals versus vaccinated cohorts, with significant overlap between pregnancy and postpartum vaccination groups. Conclusions: Although both COVID-19 vaccination and disease elicit sustained COVID-19-related antibodies in breastmilk, COVID-19 infection elicits a broader and more diverse antibody response in breastmilk, specifically with a greater secretory IgA generation. These findings support the value of maternal vaccination to safely confer mucosal immunity to neonates and the need for optimized vaccine formulations for mucosal immunity. Full article

Background/Objectives: HXP-GPOVac is a locally produced, inactivated Newcastle disease virus-based (NDV-HXP-S) COVID-19 vaccine manufactured in Thailand. This phase II trial compared its safety and immunogenicity with the mRNA vaccine BNT162b2 in adults aged 18–75 years. Methods: In this randomized, double-blind, active-controlled trial registered with the Thai Clinical Trials Registry (TCTR20220819003), 300 participants were assigned 3:1 to receive HXP-GPOVac or BNT162b2 on Days 1 and 29. Solicited adverse events (AEs) were recorded for 7 days after each dose, AEs were summarized through 28 days after each dose, and serious adverse events (SAEs), medically attended AEs (MAAEs), and adverse events of special interest (AESIs) were collected through Day 197. Humoral immunogenicity was assessed by pseudovirus 50% neutralization titers (NT₅₀) and anti-spike IgG concentrations at baseline, Day 29, Day 43, and Day 197. Seroconversion was defined as a ≥4-fold increase from baseline. A predefined subset underwent interferon-γ (IFN-γ) and interleukin-5 (IL-5) ELISpot assays to assess cell-mediated immune responses. The primary immunogenicity analysis assessed non-inferiority of HXP-GPOVac compared with BNT162b2 based on the NT₅₀ geometric mean titer ratio, with a prespecified non-inferiority margin of 0.5. Results: Solicited AEs were predominantly mild and occurred more frequently after the first dose in both groups; one or more solicited local or systemic AEs were reported by 23.7% (95% CI: 18.3–29.8) of HXP-GPOVac recipients and 44.7% (95% CI: 33.3–56.6) of BNT162b2 recipients after the first dose. AEs through 28 days after vaccination and SAEs were uncommon; MAAEs occurred in 17.0% of HXP-GPOVac recipients and 22.4% of BNT162b2 recipients, and none were considered related to vaccination. In the HXP-GPOVac group, NT₅₀ geometric mean titers increased from 5.6 at baseline to 65.5 at Day 29 and 505 at Day 43, declining to 63.6 at Day 197. Anti-spike IgG geometric mean concentrations rose from 7.5 BAU/mL at baseline to 102.7 BAU/mL at Day 29 and 514.6 BAU/mL at Day 43, decreasing to 61.0 BAU/mL at Day 197. BNT162b2 induced higher antibody levels at all time points. The NT₅₀ GMT ratio (HXP-GPOVac/BNT162b2) at Day 43 was 0.51 (95% CI: 0.39–0.67); the lower bound did not exceed the prespecified non-inferiority margin of 0.5, and non-inferiority was not established. Seroconversion rates at Day 43 were 97.6% for HXP-GPOVac and 97.1% for BNT162b2 (neutralizing antibody) and 98.6% and 97.1%, respectively (anti-spike IgG). ELISpot analyses demonstrated increased IFN-γ responses after the second dose without evidence of Th2-dominant skewing. Conclusions: HXP-GPOVac was well tolerated and induced substantial humoral and cellular immune responses, with high seroconversion rates and balanced T-cell polarization. Although absolute antibody levels were lower than those induced by BNT162b2 and the prespecified non-inferiority criterion was not met, these findings support continued evaluation of the inactivated NDV-HXP-S vaccine platform. Full article

The surface spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a key target for the development of Coronavirus Disease 2019 (COVID-19) vaccines. Nevertheless, the mutations in the S protein, particularly in its receptor-binding domain region, have resulted in a reduced or complete loss of immunogenicity and/or protective efficacy in early vaccines against the Omicron variant and subvariants. Accordingly, continuous efforts are required to develop effective vaccines against multiple Omicron subvariants to reduce current and future threats. In this study, we designed an mRNA vaccine targeting the S protein of a recent Omicron-XEC subvariant (XEC-S-mRNA) and assessed its immunogenicity, including its broad neutralizing activity, and its protective efficacy against multiple Omicron subvariants. Our results demonstrated that the lipid nanoparticle-formulated mRNA vaccine formed an appropriate particle size with strong stability and successful antigen expression. It elicited durable cellular immune responses and broad neutralizing antibodies against multiple early and recent Omicron subvariants, thereby cross-protecting transgenic mice from challenge with a heterologous Omicron strain (KP.3). Moreover, the vaccine-induced neutralizing antibodies alone were sufficient to prevent Omicron-KP.3 infection. Overall, this study shows promise for further development of the candidate vaccine against current and future Omicron infections. Full article

The pseudovirus neutralization (PNT) assay is an established high-throughput, robust, and efficient BSL-2 method for detecting neutralizing antibodies (NAbs) against SARS-CoV-2 with the correlates of protection previously established for the ancestral (Wuhan) strain. The PNT assay was validated using nonmatched ancestral sera with anti-JN.1 cross-NAbs, clinically matched JN.1 sera with anti-JN.1 NAbs, or nonmatched JN.1 sera with anti-LP.8.1, KP.2, or KP.3 cross-reacting NAbs. In line with predefined validation acceptance criteria, the PNT assay was precise, with %GCV ≤ 50 in ~90–100%/200 results (40 samples/strain). The acceptance criteria were met for linearity (slope ranged from 1.041 for ancestral sera with anti-JN.1 NAbs to 1.213 for JN.1 sera with anti-KP.2 NAbs), R² (0.9619–0.9944 for ancestral sera with anti–JN.1 NAbs), % relative bias, and total %GCV < 50 for almost all of the 15 serum samples tested for four virus strains. Human sera collected pre–COVID-19 had no detectable titer for tested Omicron JN.1 subvariants (<LLOQ) and all influenza and RSV clinical samples tested negative (<LLOQ) for SARS-CoV-2 and highly immunogenic for seasonal influenza or RSV post-vaccination, demonstrating the PNT assay specificity. Our data suggest this assay is suitable for assessing immune responses to ancestral and current SARS-CoV-2 strains and has potential for evaluating cross-reacting NAbs against emerging Omicron JN.1 subvariants. Full article

The COVID-19 pandemic highlighted the critical role of serological assays in understanding antiviral immune responses, monitoring vaccine efficacy, and informing public health strategies. This review provides a comprehensive overview of commonly used SARS-CoV-2 antibody detection methods, focusing on binding and neutralization assays. Antibody binding assays, including enzyme-linked immunosorbent assays (ELISAs), chemiluminescence immunoassays (CLIAs), lateral flow immunoassays (LFAs), and multiplex platforms, enable the rapid and high-throughput detection of immunoglobulin isotypes against various viral antigens. Neutralization assays, including live-virus, pseudovirus (PsV), and surrogate assays, offer functional insights into the ability of antibodies to prevent viral entry, though they often require higher biosafety levels and optimization. Serological assays, primarily antibody binding assays and several surrogate neutralization assays, received Emergency Use Authorization (EUA) during the pandemic, supporting seroprevalence efforts. Antibody binding assays and neutralization assays were also widely used in vaccine immunogenicity studies. Despite many standardization initiatives, assay standardization and data harmonization remain challenging and require further efforts. The choice of assay should be guided by study goals: antibody binding assays are preferred for high-throughput monitoring and epidemiological studies, while neutralization assays are essential for assessing functional immunity and variant-specific neutralization and protection. Full article

Background: Despite hybrid and vaccine-induced immunity, SARS-CoV-2 continues to cause disease. The characterization of humoral and cellular immune responses is essential for guiding prevention strategies and booster dose policies; Methods: A prospective cohort study was conducted with 131 hospitalized patients with confirmed COVID-19 in the Aburrá Metropolitan Valley, Colombia. Clinical and immunological data were evaluated on days 1–3, days 5–7, days 8–12, and 4–5 months after diagnosis. Humoral immunity was assessed by enzyme-linked immunosorbent assay (ELISA), chemiluminescent microparticle immunoassay (CMIA), and neutralization testing, and cellular immunity by CD4⁺/CD8 T-cell responses. Results: vaccinated patients had higher baseline levels of IgG and neutralizing antibody positivity than unvaccinated patients (ELISA 89.1% vs. 60.0%; CMIA 86.4% vs. 50.0%; neutralizing antibodies 88.2% vs. 65.0%), but cases of severe disease occurred in both groups. Adults aged ≥65 years had higher antibody positivity, but severe disease persisted. Mortality at 28 days was 7.6%, mainly among critically ill patients with comorbidities. Antibodies persisted at 4–5 months but were lower in those with severe acute disease. Those who received the booster dose showed stronger CD4⁺/CD8⁺ activation (notably against the Omicron variant) than unvaccinated/partially vaccinated patients. Conclusions: Vaccination improved humoral and cellular responses, but severe breakthrough infections still occurred, particularly in high-risk patients. Full article

Background/Objective: This study is a cross-sectional investigation of long-term immune responses measured at different time intervals after COVID-19 infections, vaccinations, or combined exposure. The focus is on immune reactivity against recombinant spike (S) and nucleocapsid (N) protein antigens. Materials and Methods: Serum antibody levels were assessed up to four to four and a half years after infection or immunization, including virus-specific immunoglobulin G (IgG), IgA and IgM antibodies, as well as neutralizing antibodies against the S-protein. Cellular immunity was assessed by analyzing peripheral blood mononuclear cells (PBMC; n = 43 in first cohort, n = 32 in second cohort), including T-helper memory and cytotoxic subsets, and cytokine production after in vitro stimulation with recombinant SARS-CoV-2 proteins. A multiplex cytokine assay was used to analyze effector and regulatory immune responses. Results: Virus-specific IgG antibodies persisted for years after exposure to SARS-CoV-2, with IgG against the receptor-binding domain (RBD) correlating most strongly with neutralizing activity. Vaccinated individuals demonstrated higher IgA responses, whereas antibodies to the N-protein were associated with previous infection. No IgM antibodies were detected in any subjects, suggesting an immune response based on memory rather than ongoing infection. PBMCs from individuals with a history of both COVID-19 exposure and vaccination exhibited enhanced responsiveness, characterized by increased frequencies of memory T cells compared to vaccination alone. Stimulating with the S-protein induces higher cytokine production, including IFN-gamma, TNF-alfa, and IL-12(p70), compared with stimulation by the N-protein. Cytokines such as IL-10 and TGF-beta are also elevated, suggesting immune regulation rather than persistent inflammation. Conclusions: SARS-CoV-2 infection and vaccination are associated with persistent humoral and cellular immune responses detectable several years after exposure. Individuals with hybrid immunity exhibit broader and functionally enhanced immune reactivity, indicating more robust long-term immune memory. Future studies should focus on the long-term consequences of hybrid immunity and optimize other vaccine strategies, including recombinant antigen vaccines. Full article

Background/Objectives: This study evaluated the Omicron LP.8.1 variant-adapted BNT162b2 mRNA vaccine (LP.8.1-adapted BNT162b2). Methods: This analysis is part of an ongoing phase 3 open-label study evaluating the immunogenicity, safety, and tolerability of LP.8.1-adapted BNT162b2. Reported here are descriptive 2-week post-vaccination results in 18–64 -year-olds at high risk of severe COVID-19 and in ≥65-year-olds who received the Omicron KP.2-adapted COVID-19 vaccine ≥ 6 months previously. Primary immunogenicity endpoints included neutralizing antibody geometric mean titers (GMTs) against LP.8.1 and KP.2 at 2 weeks after vaccination and geometric mean fold rises from baseline to 2 weeks after vaccination. Results were compared with a historical control group of adults who received KP.2-adapted BNT162b2 in a previous study. Tolerability and safety were also assessed. Results: Overall, 104 participants received LP.8.1-adapted BNT162b2 (18–64-year-olds, n = 51; ≥65-year-olds, n = 53). Baseline neutralizing GMTs were higher in LP.8.1-adapted BNT162b2 recipients than in the historical control group of KP.2-adapted BNT162b2 recipients against both sublineages (248 vs. 157 against LP.8.1; 372 vs. 187 against KP.2). Serum-neutralizing LP.8.1 and KP.2 GMTs increased 2 weeks after vaccination with LP.8.1-adapted BNT162b2 (1752 against LP.8.1; 2104 against KP.2) and historical control groups (1555 and 2395, respectively), and across both age groups. Reactogenicity events with LP.8.1-adapted BNT162b2 were generally mild or moderate and occurred at generally similar frequencies in both age groups. Adverse events were reported in 4.8% of participants (all in 18–64-year-olds); no serious adverse events were reported. Conclusions: After 2 weeks of follow-up, and in a small sample size, LP.8.1-adapted BNT162b2 was immunogenic in ≥65-year-olds and ≥18-year-olds at high risk of severe COVID-19. The safety and tolerability profile for LP.8.1-adapted BNT162b2 was consistent with the current US prescribing information for BNT162b2 and that of other variant-adapted BNT162b2 vaccines (Clinicaltrials.gov Identifier: NCT07069309, registered 16 July 2025). Full article

While current influenza vaccines often lack broad protection against antigenically drifted strains, some modified hemagglutinin (HA) protein antigens have shown promise in eliciting broadly neutralizing antibodies against conserved epitopes. During infection, the mildly acidic environment of the late endosome triggers irreversible HA conformational changes resulting in a post-fusion structure with altered antigenicity. While enhancing the stability of other structural class I viral fusion protein antigens has been instrumental in improving the effectiveness of COVID-19 and RSV vaccines, the role of HA stability in influenza vaccine immunogenicity is relatively unclear. Here, we used the nucleoside-modified mRNA-LNP platform to test engineered HA antigens with specific acid-stabilizing mutations (E47K, K58I, R106K, and K153E) in the HA stalk. All mutations increased HA acid stability, but E47K and R106K did not increase immunogenicity. K153E and K58I, but not E47K and R106K, enhanced the cell-surface expression of the HA protein in vitro. In mice, K153E- and K58I-containing mRNA-LNP vaccines elicited increased neutralizing antibody titers against homologous virus. K153E conferred greater protection than wild-type vaccine against lethal heterologous A/PR/8/34 challenge at low doses (0.5–1.0 µg), despite the absence of neutralizing antibodies against the challenge strain. K153E also elicited greater expansion of antigen-specific antibody-secreting cells (ASCs) in the bone marrow, as well as cross-reactive T follicular helper (Tfh) cells in the spleen. For the vaccines studied, increased HA expression was a stronger correlate of mRNA-LNP enhancement than increased HA stability. Full article