Using its recombinant protein nanoparticle and Matrix-M® adjuvant technology platform, Novavax has developed both a COVID-19 Influenza Combination vaccine (CIC) and a trivalent nanoparticle influenza hemagglutinin vaccine (tNIV). Here, we report on an ongoing, randomized, observer-blinded trial (CIC-E-301) to evaluate the safety and immunogenicity of these vaccines in adults ≥ 65 years. In CIC-E-301, CIC is compared to Novavax's 2024-2025 COVID-19 vaccine targeting JN.1 (NVX-CoV2705) and Fluzone® High-Dose; tNIV is compared to Fluzone High-Dose.Table 1Demographics and Baseline Characteristics for CIC-E-301 – Safety Analysis SetTable 2Summary of Solicited Local Injection Site Adverse Events within 7 Days of Vaccination for CIC-E-301 – Local Reactogenicity Analysis Set A total of 1985 participants in Australia and New Zealand received a single dose of either CIC, NVX-CoV2705, tNIV, or Fluzone High-Dose in a 3:2:1:3 ratio, respectively. The tolerability and safety of CIC and tNIV were evaluated by assessing reactogenicity for 7 days post dose and unsolicited adverse events (AEs) through Day 28. Immunogenicity was also assessed, with sera collected 28 days post dose and analyzed for vaccine-homologous influenza A and B strain neutralizing antibody (NAb) responses and influenza hemagglutination inhibiting antibodies, and for SARS-CoV-2 NAb responses to the JN.1 strain of SARS-CoV-2. Analyses of data are descriptive, with no prespecified statistical hypotheses.Table 3Summary of Solicited Systemic Adverse Events within 7 Days of Vaccination for CIC-E-301 – Systemic Reactogenicity Analysis SetTable 4Overall Summary of Unsolicited Adverse Events through Day 28 for CIC-E-301 – Safety Analysis Set Demographic and baseline characteristics were balanced across the vaccine groups. Overall, the median age of participants was 71 years, 54.5% male/ 45.5% female, 91.2% White, with median time since last COVID-19 vaccination of 46.7 weeks. A single dose of CIC or tNIV had an acceptable safety and tolerability profile. Solicited local and systemic reactogenicity AEs, respectively, were reported more frequently following CIC (66.7%, 42.3%) and tNIV (64.8%, 44.0%) than NVX-CoV2705 (36.4%, 31.5%) and Fluzone High-Dose (48.7%, 36.2%). Most reactogenicity events in the CIC and tNIV recipients were Grade 1 (∼1% Grade 3) including local tenderness and pain, muscle pain, and fatigue. Unsolicited TEAEs, including related and/or severe TEAEs, MAAEs, and SAEs (reported for 0.5% - 1.4%) were noted at similar frequencies across the vaccine groups. There were no AESIs reported for CIC or NVX-CoV2705, 1 (0.5%) for tNIV, and 3 (0.5%) for Fluzone High-Dose. There were no events of myocarditis/pericarditis or death. Chijioke Bennett, MD, MPH, MBA, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Katherine Smith, M.D., Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Wayne Woo, MS, Novavax, Inc: Employee|Novavax, Inc: Stocks/Bonds (Public Company) Susan Neal, n/a, Novavax Inc.: employee|Novavax Inc.: Stocks/Bonds (Public Company) Joyce S. Plested, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Tim Vincent, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Mingzhu Zhu, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Shane Cloney-Clark, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Bridget Riviers, Ph.D., Novavax, Inc: Employee|Novavax, Inc: Stocks/Bonds (Public Company) Miranda R. Cai, PhD, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Pratyusha Kajipet, M.S., Novavax: employee|Novavax: Stocks/Bonds (Public Company) Zhaohui Cai, PhD, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Iksung Cho, MS, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Raburn M. Mallory, M.D., Novavax: I am an employee of Novavax|Novavax: Stocks/Bonds (Public Company) Robert Walker, M.D., Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company)

A productive and antigen-specific immune response requires four essential components from a cancer vaccine: tumor antigens, formulations, immune adjuvants, and delivery vehicles. There is a growing need for safe and effective adjuvants tailored to cancer vaccines, which require strong cellular immunity. Matrix-M®, a saponin-based adjuvant derived from purified Quillaja saponaria bark, is known to enhance immune responses by promoting immune cell recruitment, Th1 polarization, and inflammasome activation. Early distribution of Matrix-M to draining lymph nodes contributes to the generation of long-lasting memory B cells and broad-based T-cell immunity1. Matrix-M–containing vaccines against some infectious diseases were shown to be safe and immunogenic across age groups2-7. Importantly, Matrix-M is compatible with multiple vaccine platforms. Beyond its established role in infectious disease vaccines, Matrix-M is being evaluated as a potential adjuvant for cancer immunotherapy. Recent findings reveal that Matrix-M enables antigen cross-presentation on MHC class I molecules by inducing a process called lysosomal membrane permeabilization (LMP)—a key event that facilitates antigen escape into the cytosol8. Following uptake by bone marrow–derived dendritic cells, Matrix-M and antigen show a high level of co-localization in the endosome, which subsequently enables efficient Matrix-M-induced cross-presentation. The localization of Matrix-M and antigen in the same endosome could potentially be enhanced by linking antigens to Matrix-M, which has been described for Matrix-M and avian influenza trimers9. The Matrix-M induced LMP supports the generation of cytotoxic CD8+ T cells, a critical component of anti-tumor immunity. These insights into the intracellular mode of action of Matrix-M promoting antigen cross-presentation and CD8+ T-cell priming highlight its potential to enhance the efficacy of prophylactic and therapeutic cancer vaccines.: References: 1) Carnrot, C. et al.Frontiers in Drug Delivery 3 (2023). 2) Datoo, M. S. et al. Lancet 403, 533-544 (2024). 3) Anez, G. et al. JAMA Netw Open 6, e239135 (2023). 4) Sang, S. et al. Wellcome Open Res 8, 450 (2023). 5) Venkatraman, N. et al. Lancet Microbe 6, 100868 (2025). 6) Shinde, V. et al. Lancet Infect Dis 22, 73-84 (2022). 7) Fries, L. et al. J Infect Dis 222, 572-582 (2020). 8) Zarnegar, B. et al. NPJ Vaccines 10, 184 (2025). 9) Patel, N. et al. Nat Commun 16, 6625 (2025). Berit Carow, Linda Stertman, Jonathan Fix, Sarah Sellers, Raj Kalkeri, Cecilia Carnrot, Joyce S. Plested, Robert Walker, Ruxandra Draghia-Akli. Matrix-M adjuvant – A promising adjuvant for preventative and therapeutic cancer vaccines development [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr C066.

INTRODUCTION:Immunosuppressed individuals are at increased risk of coronavirus disease (COVID-19). Although mRNA vaccines have shown efficacy in these populations, data on protein-based vaccines remain limited. We evaluated the immunogenicity and safety of Novavax COVID-19 vaccine (NVX-CoV2601) in immunosuppressed patients. METHODS:This single-center, prospective ARMOR study included adults with inflammatory bowel disease (IBD) or solid organ transplant recipients receiving immunosuppressive therapy who had received ≥3 prior COVID-19 vaccine doses. Participants received one NVX-CoV2601 booster with follow-up at one and six months. The primary outcome was change in humoral immunogenicity from baseline to one month post-vaccination. RESULTS:Twenty-one immunosuppressed patients (18 IBD, 3 solid organ transplant recipients) were enrolled and compared with 57 age/sex-matched healthy controls. In ARMOR participants, anti-spike IgG GMT increased significantly post-immunization (22,969 to 66,639 EU/mL; 2.9-fold increase, p = 0.001). Healthy controls increased from 54,812 to 129,813 EU/mL (2.4-fold increase; p < 0.001). After baseline adjustment, no significant difference existed between groups at day 28. At 6 months, antibodies waned faster in immunosuppressed subjects. NVX-CoV2601 was well tolerated without IBD flares or organ rejection. CONCLUSION:NVX-CoV2601 was safe and immunogenic with similar humoral responses compared to healthy controls, making it a viable alternative for immunosuppressed patients.

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.

Based on viral evolution, increases in seasonal infections, and facilitation of delivery, an annual combination vaccine simultaneously targeting influenza and SARS-CoV-2 would benefit public health. The safety and immunogenicity of a COVID-19-Influenza Combination nanoparticle vaccine (CIC) containing SARS-CoV-2 recombinant spike (rS) to the ancestral strain (Wuhan) and quadrivalent influenza hemagglutinin with a Matrix-M® saponin-based adjuvant were evaluated in a phase 1/2 blinded, randomized trial. The safety, tolerability, and immunogenicity of a CIC two-dose series were assessed and compared with standalone quadrivalent influenza (qNIV) and monovalent COVID-19 (NVX-CoV2373) vaccines. Reactogenicity events, unsolicited adverse events (AEs), antiviral microneutralization responses, hemagglutination-inhibition antibody titers, anti-rS protein immunoglobulin G, and human angiotensin-converting enzyme 2 receptor binding inhibition antibody responses for SARS-CoV-2 were measured. All participants had been previously vaccinated against ancestral SARS-CoV-2. From September 8, 2021, to April 22, 2022, 642 participants were enrolled and randomized into the study; 637 received at least one vaccination. After each dose, CIC formulations induced antibody responses against homologous and heterologous influenza and SARS-CoV-2 strains that were comparable with the references. The CIC vaccine group had similar incidence of solicited and unsolicited AEs as the qNIV and NVX-CoV2373 reference groups. Severe unsolicited AEs only occurred in the CIC group but were infrequent and not considered related to the study vaccine. Overall, CIC formulations displayed reference-comparable safety and immunogenicity and provided data for statistical modeling analyses to optimize influenza hemagglutinin and SARS-CoV-2 rS antigen concentrations for use in phase 2 clinical trials investigating CIC.

Mucosal immunity, including antibodies like immunoglobulin A (IgA), function as the body's first line of defense in the respiratory tract, particularly against viruses. An anti-rS protein IgA enzyme-linked immunosorbent assay (ELISA) was developed using the Omicron XBB.1.5 subvariant of SARS-CoV-2 and was validated to demonstrate the suitability of the method for testing saliva from SARS-CoV-2 vaccine clinical trials. This assay successfully met acceptance criteria for inter-/intra-assay precision, specificity, selectivity, linearity, lower/upper limits of quantitation, and assay robustness. The IgA in saliva was stable for up to 7 freeze/thaw cycles, for up to 48 h at 24 °C, up to 7 days at 4 °C, up to 3 weeks at -20 °C, and up to 1 year at -80 °C. After validation using Omicron XBB.1.5 rS protein, cross-reactivity was demonstrated with the SARS-CoV-2 variant JN.1. This validated IgA assay can be a valuable tool to assess mucosal IgA levels in SARS-CoV-2 clinical trials.

Proportional increases in anti-Spike (S) IgG4 associated with decreased Fc effector functions have been reported following repeated mRNA, but not recombinant protein-based (rS) (NVX-CoV2373, Novavax, Inc.), SARS-CoV-2 vaccination. We demonstrate the first evidence of a negative correlation between anti-S IgG4 and neutralizing antibody (nAb), as well as antibody-dependent surrogate Fc effector functions. Priming with two NVX-CoV2373 vaccines followed by a third dose was associated with higher IgG1 and IgG3, lower IgG4, higher nAb titers and surrogate Fc effector functions versus mRNA. Immune imprinting of anti-S IgG4 and nAbs, and Fc effector function imprinting after mRNA priming was observed. This effect was partially overcome by updated XBB.1.5 protein subunit vaccination, but not by ancestral vaccine strains. We establish correlation of anti-S IgG4 responses to reduced nAbs and surrogate Fc effector functions and demonstrate the impact of additional booster vaccination on subsequent immune response and Fc effector functions in the context of ancestral and XBB.1.5 strains.

OBJECTIVES:Safety and immunogenicity assessment of updated monovalent and bivalent SARS-CoV-2 vaccines in adolescents. METHODS:This phase 3, double-blinded study randomised 12-<18-year-old participants, who received ≥2 prior doses of an approved/authorised mRNA-based COVID-19 vaccine, 1:1 to receive NVX-CoV2601 (XBB.1.5) or a bivalent vaccine (NVX-CoV2373 [Wuhan] + NVX-CoV2601). The primary immunogenicity endpoint was day-28 neutralising antibody (nAb) geometric mean titres (GMTs) against XBB.1.5. Safety endpoints were solicited reactogenicity ≤7 days and unsolicited adverse events (AEs) ≤28 days post-vaccination and frequency/severity of predefined AEs of special interest through day 180. RESULTS:Of 401 randomised participants, nAb GMTs against XBB.1.5 increased (GMFR [95% CI]) for both NVX-CoV2601 (12.2 [9.5-15.5]) and the bivalent vaccine (8.4 [6.8-10.3]); post-vaccination responses to ancestral SARS-CoV-2 and the JN.1 variant were also observed. Increases in anti-spike IgG levels were comparable between the groups. Solicited and unsolicited AEs were mild to moderate, with similar occurrence among the groups. Severe and serious events were rare and unrelated to the study vaccines; no PIMMCs or myocarditis/pericarditis were reported. CONCLUSIONS:NVX-CoV2601 elicited more robust antibody responses to XBB.1.5 and ancestral virus, compared with a bivalent formulation. The safety profile within each group was consistent with NVX-CoV2373, which contains ancestral recombinant spike protein.

Abstract Background There is a public health need for annual immunizations against both SARS-CoV-2 and influenza viruses. We developed both a standalone saponin-adjuvanted (Matrix-M™) recombinant quadrivalent hemagglutinin (HA) nanoparticle influenza vaccine (qNIV), and a COVID and influenza combination (CIC) vaccine, comprising recombinant SARS-CoV-2 Spike (rS) (NVX-CoV2373), qNIV, and Matrix-M adjuvant.Table 1.Study design Methods Participants in Australia and New Zealand (1571 treated, including 864 in the CIC group) aged 50–80 years were randomized equally to receive one intramuscular dose of vaccine in 1 of 20 groups: either 1 of 11 different dose/formulations of CIC, 1 of 3 formulations of qNIV with Matrix-M, 1 of 4 formulations of standalone rS with Matrix-M, or 1 of 2 influenza vaccine comparators (Fluzone HD® or FLUAD®) (Table 1). Immunogenicity assessments included anti-spike IgG, SARS-CoV-2 neutralizing antibody (vaccine-homologous and -heterologous strains), wild-type influenza HAI antibodies (vaccine-homologous strains). Reactogenicity was assessed for 7 days following vaccination and SAEs, AESIS, and MAAEs were assessed throughout the study.Table 2.CIC and qNIV post-vaccination immunogenicity assessments (Day 21, per-protocol analysis set) Results qNIV ([HA60/M75], n=75) HAI and neutralizing antibody responses were significantly higher than FLUAD and Fluzone HD against both vaccine-homologous A strains, particularly against H3N2 (Table 2). CIC ([HA60/rS35/M75], n=75) showed evidence of rS and HA antigen interference, but achieved anti-spike IgG and influenza HAI antibody responses that were comparable to both the standalone rS vaccine (NVX-CoV2373) and FLUAD /Fluzone HD, respectively (Table 2). All qNIV and CIC formulations evoked local and systemic solicited adverse events at rates and severities less than or comparable to FLUAD and Fluzone HD (Figure 1). There was no dose dependence of HA, rS antigens, or Matrix-M on tolerability. SAEs were infrequent in all groups.Figure 1.Solicited (A) local and (B) systemic TEAEs within 7 days of vaccination (safety analysis population) Conclusion qNIV produced improved wild-type HAI antibody responses as compared to FLUAD and Fluzone HD against influenza A strains, notably against H3N2. CIC achieved both anti-spike IgG responses comparable to the authorized prototype NVX-CoV2373 rS vaccine and HAI responses comparable to licensed enhanced influenza comparators. CIC and qNIV had safety profiles comparable to Fluzone HD and FLUAD. Disclosures Vivek Shinde, MD, MPH, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Joyce S. Plested, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Tim Vincent, n/a, Novavax, Inc.: Employee|Novavax, Inc.: Stocks/Bonds (Public Company) Mingzhu Zhu, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Shane Cloney-Clark, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Zhaohui Cai, PhD, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Bridget Riviers, Ph.D., Novavax, Inc.: Employee|Novavax, Inc.: Stocks/Bonds (Public Company) Farnaz Mahkhou, Ph.D., Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Anthony M. Marchese, PhD, Novavax Inc: Employee|Novavax Inc: Stocks/Bonds (Public Company) Iksung Cho, MS, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Louis F. Fries, III, MD, Novavax, Inc.: contractor for Novavax|Novavax, Inc.: Stocks/Bonds (Public Company) Wayne Woo, MS, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company)

Background Authorities globally recommended a monovalent omicron XBB.1.5-based COVID-19 vaccine for the 2023-24 season. The Novavax COVID-19 vaccine, NVX-CoV2601, contains XBB.1.5 recombinant spike protein, based on an authorised prototype vaccine (NVX-CoV2373) technology.We aimed to determine whether a single dose of NVX-CoV2601 versus NVX-CoV2373 (from a previous study [2019nCoV-311 part 2]) produced superior neutralising antibody (nAb) responses, and non-inferior seroresponse rates to XBB.1.5, after three or more previous mRNA-based COVID-19 vaccinations. Methods In part 1 of this single-arm, phase 2/3 study (2019nCoV-313), participants aged 18 years or older who had been previously vaccinated with three or more doses of mRNA-1273 (Moderna) or BNT162b2 (Pfizer-BioNTech) were enrolled across 30 US centres (research groups and universities) located across 20 states. Participants received one intramuscular injection of NVX-CoV2601 (5 mu g XBB.1.5 spike plus 50 mu g Matrix-M adjuvant). Coprimary endpoints were superiority of baseline-adjusted nAb geometric mean XBB.1.5 titres (adjusted GMTs), with superiority declared when the lower bound of the 95% CI for the GMT ratio (GMTR) was greater than 1, and non-inferiority of seroresponse rates, with non-inferiority declared when the lower bound of the 95% CI for the seroresponse rate difference was greater than-10%, on day 28; comparisons were made for NVX-CoV2601 administered in this study versus NVX-CoV2373 administered in part 2 (group G) of the 2019nCoV-311 study. Coprimary endpoints were assessed in the per-protocol immunogenicity set (ie, all participants who received study vaccine, underwent 28 days of follow-up, had day 0 and day 28 samples available, and had no major protocol deviations). Safety was a secondary endpoint and included assessments of solicited treatment-emergent adverse events up to 7 days and unsolicited treatment-emergent adverse events up to 28 days after vaccination in the safety analysis set (ie, all participants who received study vaccine). Here we report the prespecified interim analysis of immunogenicity and safety up to day 28. This study is registered with ClinicalTrials.gov, NCT05975060, and is now complete. Findings Between Sept 7 and Sept 8, 2023, 380 individuals were screened, of whom 332 were enrolled and received study vaccine. At the 28-day interim analysis database lock (Jan 17, 2023), the per-protocol analysis sets included 309 (93%) of 332 NVX-CoV2601 recipients and 227 (90%) of 252 NVX-CoV2373 recipients. Mean age of NVXCoV2601 recipients was 521 years (SD 161); 192 (62%) of 309 were female and 117 (38%) were male. Mean age of NVX-CoV2373 recipients was 422 years (134); 128 (56%) of 227 were female and 99 (44%) were male. At day 28, the baseline-adjusted nAb GMT for NVX-CoV2601 was 9059 (95% CI 8071-10168) and for NVX-CoV2373 was 1566 (1370-1790); the between-group adjusted GMTR was 58 (95% CI 49-69). In the per-protocol immunogenicity set, seroresponse rates were 64% (196 of 305) among recipients of NVX-CoV2601 and 7% (16 of 227) among recipients of NVX-CoV2373, with a seroresponse rate difference of 57% (95% CI 51-63). In the NVX-CoV2601 group, within 7 days, solicited local treatment-emergent adverse events were reported in 189 (57%) of 332 participants (including one [<1%] grade 3 or worse event; tenderness) and solicited systemic treatment-emergent adverse events were reported in 158 (48%) participants (including four [1%] participants with one or more grade 3 events; malaise [n=3], headache [n=2], fatigue [n=1], and muscle pain [n=1]). The most common solicited treatment-emergent adverse events were tenderness (171 [52%]) and pain (98 [30%]) at the injection site, fatigue (97 [29%]), and muscle pain (97 [29%]). Up to day 28, unsolicited adverse events considered related to study vaccination in the NVX-CoV2601 group occurred in five (2%) participants (one for each of asthma, axillary pain, diarrhoea, hypertension [which was medically attended], and presyncope). No serious adverse events due to study product, adverse events of special interest, or deaths due to study product occurred, and no study discontinuations due to treatment-emergent adverse events occurred. Interpretation The coprimary endpoints were met, and NVX-CoV2601 was well tolerated. These interim data support NVX-CoV2601 use per guidance for XBB.1.5-directed COVID-19 vaccines and demonstrate the adaptability of this vaccine platform for updated SARS-CoV-2 spike proteins. Copyright (c) 2025 Elsevier Ltd. All rights reserved, including those for text and data mining, AI training, and similar technologies.

BACKGROUND:To support heterologous vaccine regimens, periodic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) revaccination requires immunogenicity and safety data for adjuvanted protein-based vaccines following prior mRNA doses. OBJECTIVE:We sought to assess noninferiority of neutralizing antibody (nAb) titers following a second dose versus a first dose (in a prior study) of an SARS-CoV-2 protein-based vaccine (NVX-CoV2373) administered following a primary series (2 or 3 doses) of an mRNA vaccine. METHODS:This phase 3, open-label study (2019nCoV-312/NCT05875701) enrolled participants who had received 1 dose of the ancestral SARS-CoV-2 protein-based vaccine in an earlier study (2019nCoV-307/NCT05463068) after a primary series (2 or 3 doses) of a commercial mRNA vaccine. In the current study, participants received an additional dose of protein vaccine (ancestral [n = 104] or Omicron BA.5 [n = 40]) at least 180 days after their previous study dose. RESULTS:The study enrolled 144 participants. The ratio of anti-Wuhan nAbs (geometric mean titer) at day 28 after this study dose (ancestral 393.2 IU/mL [95% CI 318.0-468.2]) versus previous study dose (396.6 IU/mL [95% CI 328.7-478.6]) was 1.0 (0.8-1.2), meeting noninferiority. The seroresponse rate difference between doses was 7.4% (95% CI -1.2% to 16.5%), also meeting noninferiority. Omicron BA.5 nAb titers suggest cross-protection against emerging variants. The anti-Wuhan nAb ratio at day 28 between Omicron BA.5 vaccine dose in this study (835.0 [597.1-1167.6]) versus the ancestral vaccine in the previous study (436.0 [305.6-622.2]) was 1.9 (1.5-2.5), exceeding superiority criterion. Local and systemic reactions were similar between doses and strains in both studies. CONCLUSION:A heterologous regimen of 2 adjuvanted, recombinant spike protein vaccine doses following multiple mRNA vaccine doses produced robust immune responses, exhibiting cross-reactivity to some newer variants.

Background: Seasonal (2023-2024) COVID-19 vaccine recommendations included updates against Omicron XBB.1.5. NVX-CoV2601 contains XBB.1.5 recombinant spike (rS) protein, Matrix-M (R) adjuvant, and is based on authorized prototype vaccine (NVX-CoV2373) technology. Immunogenicity and safety outcomes 6 months after vaccination following a single dose of monovalent NVX-CoV2601 in previously vaccinated and vaccine-naive, SARS-CoV-2-seropositive participants aged >= 18 years are reported here. Methods: The phase 2/3 open-label, single-arm 2019nCoV-313 study consisted of two parts (part 1: participants with >= 3 prior mRNA vaccines; part 2: unvaccinated participants with a clinical history of COVID-19). Participants received a single dose of NVX-CoV2601. Primary endpoint analyses through day 28 were previously published. This final analysis assessed immunogenicity and safety through the end of the study (day 180). Immunogenicity data (e.g., neutralizing antibodies [nAbs] and anti-rS IgG antibodies) were summarized using geometric mean antibody levels and fold rise and seroresponse rate (SRR). Results: The safety analysis set included 332 participants in part 1 and 338 participants in part 2. In previously vaccinated participants, nAb geometric mean titers (GMTs; 95% CIs) were 120.7 (101.5-143.6) at day 0, increased to 955.5 (814.0-1121.4) at day 28, and decreased to 454.8 (382.9-540.3) at day 180. SRR decreased from 64.3% at day 28 to 41.1% at day 180. Similar results were seen in vaccine-naive, SARS-CoV-2-seropositive participants, with GMTs of 67.0 (56.6-79.3), 1296.7 (1082.6-1553.2), and 303.6 (258.5-356.4) at day 0, 28, and 180, respectively. SRR waned from 74.3% at day 28 to 45.0% at day 180. Anti-rS IgG responses similarly increased at day 28 and had moderate decreases at day 180 in both groups. No new safety signals were reported. Conclusions: A single dose of NVX-CoV2601 showed robust, durable immunogenicity in adult participants from study 2019nCoV-313 parts 1 and 2. These data support the use of NVX-CoV2601 in both populations. Trial registration: NCT05975060

BACKGROUND:Most of the population has been infected with SARS-CoV-2 and, thus, is primed by natural exposure. As such, it was assessed whether a single dose of the monovalent XBB.1.5 vaccine, NVX-CoV2601, elicited a comparable immune response to XBB.1.5 in seropositive unvaccinated participants to that in previously vaccinated participants, thereby allowing the former to forego a two-dose primary series. METHODS:In this phase 2/3, open-label, single-arm study (2019nCoV-313/NCT05975060 [group 2]), vaccine-naive participants ≥18 years with previous SARS-CoV-2 infection received one dose of NVX-CoV2601. This analysis compared the 28-day immunogenicity and safety of NVX-CoV2601 in vaccine-naive and previously vaccinated (≥3 prior mRNA-based vaccines, from 2019nCoV-313 group 1) participants. Noninferiority of neutralizing antibody (nAb) response in vaccine-naive versus vaccinated participants was the primary objective. The day-28 geometric mean titer (GMT) ratio (GMTR) and seroresponse rate (SRR; percentage of participants with a ≥4-fold rise in antibody response from baseline) were measured, and safety was assessed. RESULTS:Of the participants enrolled from September 11 to November 15, 2023, per-protocol sets included 306/338 (90.5%) vaccine-naive and 309/332 (93.1%) vaccinated participants. At day 28, adjusted GMTs (95% CI) against XBB.1.5 in the vaccine-naive and vaccinated groups were 1491.5 (1277.5-1741.4) and 841.4 (723.9-978.0), respectively. The vaccine-naive-vaccinated nAb GMTR was 1.8 (95% CI 1.43-2.20) and SRRs were 74.3% and 64.3% for vaccine-naive and vaccinated participants, respectively (SRR difference: 10.0 [95% CI 2.6-17.4]). No new safety signals or events of special interest were reported. CONCLUSIONS:A single dose of NVX-CoV2601 in vaccine-naive participants with a history of SARS-CoV-2 infection elicited a robust neutralizing antibody response that was noninferior to that observed in vaccinated participants. The vaccine was well-tolerated. These data support the use of NVX-CoV2601 as a single dose, regardless of prior vaccination history. TRIAL REGISTRATION:NCT05975060.

Abstract Background IgG4, the least abundant human IgG subtype, increases after repetitive exposure to some antigens, and may induce immune tolerance. Studies have found that repeat mRNA SARS-CoV-2 vaccination leads to large proportional increases in spike (S)-specific IgG4. By contrast, increased IgG4 has not been observed following repeat vaccination with recombinant SARS-CoV-2 S (rS) protein (NVX-CoV2373, Novavax). Whether vaccine-induced anti-S IgG4 might impair SARS-CoV-2 immunity remains unknown.Figure:Serum anti-Spike IgG1 (A), IgG3 (B), and IgG4 (C) concentrations (ng/mL) measured by ELISA were correlated with neutralizing antibody titers (MN50) measured by infectious virus microneutralization assay. Methods Sera were collected from study participants in 2019nCoV-307 (NCT05463068) and 2019nCoV-301 (NCT04611802), including 2 groups from 2019nCoV-307 who received 3 homologous mRNA doses followed by 1 NVX-CoV2373 dose (mRNA-1273, Moderna, n=10; or BNT162b2, Pfizer, n=10), and a 3rd group from 2019nCoV-301 who received 4 homologous NVX-CoV2373 doses (n=18). Sera collected ≥6 months after the last dose in the first 2 groups and ∼4 weeks after the last dose in the 3rd group were assessed for neutralizing antibodies (nAb), IgG subclass profiles (anti-S total IgG, IgG1, IgG2, IgG3, and IgG4), and Fc effector activities (cell-based ADCP assay; surrogate ADCC by FcγRIIIa binding; and ADCD by C1q binding) after repeated NVX-CoV2373 or a single NVX-CoV2373 dose following repeated mRNA vaccine.Table:Summary of correlations between IgG1, IgG3, and IgG4 with neutralizing antibody titers (ancestral) and Fc effector functions in 2019nCoV-301 and 2019nCoV-307 studies. Results Increased nAb titers after NVX-CoV2373 were observed irrespective of the prior vaccine background, whereas increased IgG4 levels were only observed in recipients of mRNA vaccines. Spearman's rank correlation between nAb and Fc functions found significant positive correlations with anti-S IgG1 and IgG3 (Figure A, B), and significant negative correlation with anti-S IgG4 (Figure C) antibody responses (Table). Conclusion These are the first data to demonstrate the negative correlation of increased SARS-CoV-2 vaccine–induced anti-S IgG4 levels and nAb titers and Fc effector functions. The limitations of our data include small sample sizes, and potential differences attributable to vaccination and serum collection intervals. IgG4-mediated suboptimal nAb and reduced Fc effector function could reduce the vaccine effectiveness of the SARS-CoV-2 response, though more work is needed to understand its impact on the optimization of vaccine platform choice. Disclosures Raj Kalkeri, PhD, Novavax: Employee|Novavax: Stocks/Bonds (Public Company) Mingzhu Zhu, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Shane Cloney-Clark, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Anand Parekh, M.Sc., Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Drew Gorinson, B.S., Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Rongman Cai, PhD, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Soham Mahato, PhD, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company) Anthony M. Marchese, PhD, Novavax Inc: Employee|Novavax Inc: Stocks/Bonds (Public Company) Louis F. Fries, III, MD, Novavax, Inc.: contractor for Novavax|Novavax, Inc.: Stocks/Bonds (Public Company) Lisa M. Dunkle, MD, Novavax, Inc: Employee|Novavax, Inc: Ownership Interest|Novavax, Inc: Stocks/Bonds (Public Company) Amy W. Chung, PhD, Novavax: Grant/Research Support Joyce S. Plested, n/a, Novavax, Inc.: employee|Novavax, Inc.: Stocks/Bonds (Public Company)

Immunoglobulin (Ig) A acts as a first line of defense against respiratory pathogens. Mucosal IgA in salivary and nasal passages has a rapid response to antigens and can play a protective role against reinfection. The mainstay for analyzing SARS-CoV-2 infection and vaccine efficacy has been assessment of serum IgG levels; however, validated assays for assessment of mucosal IgA in clinical samples are necessary as new and adapted measures are generated to combat immune-evasive viral variants. A mucosal IgA assay was developed and tested through assessment of IgA levels in salivary samples from participants of the 2019nCoV-314/NCT05973006 study. These participants had previously received ≥ 2 mRNA-based COVID-19 vaccinations prior to enrollment and received a single intramuscular study dose of NVX-CoV2601 (XBB.1.5) or bivalent vaccine (NVX-CoV2601 + NVX-CoV2373 [Wuhan]). Salivary samples were collected prior to vaccination on Day 0 and on Day 28 to assess response postvaccination. Both vaccine groups elicited a significant increase in anti-SARS-CoV-2 spike IgA against XBB.1.5. Furthermore, cross-reactivity by identification of anti-JN.1 and anti-Wuhan IgA was also observed. The detection of IgA in clinical mucosal samples using this assay will be a valuable tool in supporting vaccine development.

BACKGROUND:We evaluated the immunogenicity and safety of a dose of NVX-CoV2705, a JN.1 subvariant SARS CoV-2 rS vaccine, in adults previously vaccinated with authorized/approved COVID-19 vaccines. METHODS:Study 2019nCoV-315 is a Phase 3, open-label, single-arm study to evaluate the safety and immunogenicity of a single dose of NVX-CoV2705 in previously COVID-19-vaccinated adult participants ≥18 years of age in the United States. Participants received one dose of NVX-CoV2705. The primary immunogenicity endpoint was the geometric mean titer (GMT) of serum neutralizing antibodies against the SARS-CoV-2 Omicron JN.1 variant at Day 28 following study vaccination and seroresponse rate (SRR) in ID50 titers for the JN.1 subvariant assessed at Day 28 following study vaccination. Primary safety endpoints include local and systemic solicited adverse events (AEs) up to Day 6 post-vaccination, unsolicited AEs up to Day 28, and treatment-related MAAEs, AESIs, and SAEs through Day 180. Exploratory endpoints also provided additional data for circulating variants. RESULTS:Between October 14, 2024, and October 15, 2024, 66 participants were screened and 60 enrolled. A total of 58 participants were included in the Per-Protocol Analysis Set. GMTs increased from 138.6 (95 % CI: 88.0, 218.2) to 671.4 (95 % CI: 437.0, 1031.6) from baseline to Day 28, respectively. In addition, GMTs increased ≥3.8-fold (GMFR) from baseline (Day 0) to Day 28 for currently circulating or emerging Omicron subvariants JN.1, LP.8.1, KP.2, KP.3, KP.3.1.1, MC.1, XEC, MC.10.1, LF.7, LF.7.2.1, LF.7.7.2, NB.1.8.1, and XFC, with an acceptable safety profile after single dose vaccination. DISCUSSION:A single dose of NVX-CoV2705 induced a rapid and robust anti-SARS-CoV-2 immune response against the Omicron JN.1 and other circulating variants and had an acceptable safety profile. https://clinicaltrials.gov/study/NCT06409663.

Immunoglobulin (Ig) A acts as a first line of defense against respiratory pathogens. Mucosal IgA in salivary and nasal passages has a rapid response to antigens and can play a protective role against reinfection. The mainstay for analyzing SARS-CoV-2 infection and vaccine efficacy has been assessment of serum IgG levels; however, validated assays for assessment of mucosal IgA in clinical samples are necessary as new and adapted measures are generated to combat immune-evasive viral variants. A mucosal IgA assay was developed and tested through assessment of IgA levels in salivary samples from participants of the 2019nCoV-314/ [NCT05973006][1] study. These participants had previously received ≥2 mRNA-based COVID-19 vaccinations prior to enrollment and received a single intramuscular study dose of NVX-CoV2601 (XBB.1.5) or bivalent vaccine (NVX-CoV2601 + NVX-CoV2373 [Wuhan]). Salivary samples were collected prior to vaccination on day 0 and on day 28 to assess response post vaccination. Both vaccine groups elicited a significant increase in anti –SARS-CoV-2 spike IgA against XBB.1.5. Furthermore, cross-reactivity via identification of anti-JN.1 and anti-Wuhan IgA was also observed. The detection of IgA in clinical mucosal samples through this assay will be a valuable tool in supporting vaccine development. ### Competing Interest Statement Mingzhu Zhu, Edmond Massuda, Urvashi Patel, Gordon Chau, Raj Kalkeri, Shane Cloney-Clark, Katherine Smith, Susan Neal, Joyce S. Plested, Raburn M. Mallory, and Chijioke Bennett are salaried employees of Novavax, Inc. and hold stock. ### Clinical Trial NCT05973006 ### Funding Statement This manuscript was funded by Novavax, Inc. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The trial protocol was approved by the Advarra Institutional Review Board and Independent Ethics Committee, the study performed in accordance with the Declaration of Helsinki and the International Conference on Harmonization Good Clinical Practice guidelines, and consent was provided from all participants. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The information and data that support the findings of the study are available at https://clinicaltrials.gov/study/[NCT05973006][1]. Requests submitted to the corresponding author will be considered upon publication of this article, and deidentified participant data may be provided. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT05973006&atom=%2Fmedrxiv%2Fearly%2F2025%2F01%2F22%2F2025.01.21.25320906.atom

BACKGROUND:NVX-CoV2373, a recombinant SARS-CoV-2 spike (rS) protein vaccine with Matrix-M® adjuvant, has been authorized for use in adults and adolescents. PREVENT-19 (NCT04611802/2019nCoV-301), a pivotal phase 3, randomized, placebo-controlled trial demonstrated robust efficacy of a primary, 2-dose series of NVX-CoV2373 against COVID-19. METHODS:Protocol expansions to PREVENT-19 included enrollment of adolescents (aged 12 to <18 years) and administration of 3rd and 4th doses of NVX-CoV2373 to adults and adolescents. Participants randomized 2:1 received NVX-CoV2373 or placebo 21 days apart; 3rd and 4th doses were administered ≥6 months after the preceding dose. Secondary and additional assessments included post-3rd- and 4th-dose immune responses (neutralizing antibody [nAb], anti-rS IgG, human angiotensin-converting enzyme-2-receptor binding inhibition [hACE2-RBI]) and response durability (post-3rd dose) to ancestral virus; cross-reactivity to Omicron subvariants; safety; and reactogenicity. RESULTS:Immune responses were observed against ancestral virus after two doses of NVX-CoV2373 but not after placebo. In both adults and adolescents, additional doses of NVX-CoV2373 increased nAb titers, anti-rS IgG levels, and hACE2-RBI; durable responses were recorded 8 months post 3rd dose. nAb responses post 3rd dose were noninferior to those post primary series. Cross-reactivity to BA.5 and BQ.1.1 variants was also observed, with anti-rS IgG levels post 3rd or 4th dose exceeding previously reported correlates of protection. Additional doses of NVX-CoV2373 were well tolerated, with no new safety signals. CONCLUSIONS:NVX-CoV2373 elicited robust and durable humoral immune responses to ancestral SARS-CoV-2 as a 3rd and 4th dose after the primary series in adults and adolescents. Cross-reactivity to relevant variants provides insight into potential protection against antigenically related, but shifted, viral strains. Additional doses of NVX-CoV2373 were well tolerated with no new safety signals. These results support the utility of this vaccine platform and continued updates, based on currently circulating strains, to help effectively combat SARS-CoV-2 infection.

As variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continue to emerge, assessment of vaccine immunogenicity remains a critical factor to support continued vaccination. To this end, an in vitro microneutralization (MN50) assay was validated to quantitate SARS-CoV-2 neutralizing antibodies against prototype and variant strains (Beta, Delta, Omicron BA.1, Omicron BA.5, and XBB.1.5) in human serum. For the prototype strain, the MN50 assay met acceptance criteria for inter-/intra-assay precision, specificity, linearity, and selectivity. The assay was robust against changes to virus/serum incubation time, cell seeding density, virus content per well, cell passage number, and serum interference. Analyte in serum samples was stable up to five freeze/thaw cycles and for up to 12 months of storage at –80 ± 10 °C. Similar results were observed for the variant-adapted MN50 assays. The conversion factor to convert assay result units to WHO international standard units (IU/mL) was determined to be 0.62 for the prototype strain. This MN50 assay will be useful for vaccine immunogenicity analyses in clinical trial samples, enabling assessment of vaccine immunogenicity for ancestral and variant strains as variant-adapted vaccines are developed.