Safety and Immunogenicity of the BNT162b2 Vaccine Coadministered with Seasonal Inactivated Influenza Vaccine in Adults

Abstract Introduction Vaccination is a critical tool for preventing coronavirus disease 2019 (COVID-19) and influenza illnesses. Coadministration of the COVID-19 vaccine, BNT162b2, with seasonal inactivated influenza vaccine (SIIV) can provide substantial benefits, including streamlining vaccine delivery. Methods In this phase 3 study, healthy 18- to 64-year-olds who had received three previous doses of BNT162b2 were randomized (1:1) to the coadministration group (month 0, BNT162b2 + SIIV; month 1, placebo) or the separate-administration group (month 0, placebo + SIIV; month 1, BNT162b2). The primary immunogenicity objective was to demonstrate that the immune responses elicited by BNT162b2 and SIIV [measured by full-length S-binding immunoglobulin G (IgG) levels and strain-specific hemagglutination inhibition assay (HAI) titers against four influenza strains 1 month post-vaccination, respectively] when coadministered were noninferior to those elicited by either vaccine administered alone, based on a prespecified 1.5-fold noninferiority margin [lower bound 95% CI for geometric mean ratio (GMR) > 0.67]. Reactogenicity and adverse event (AE) rates were evaluated. Results Randomized participants who received study vaccination (N = 1128; coadministration group, n = 564; separate-administration group, n = 564) had a median age of 39 years. Model-adjusted GMRs for coadministration to separate administration were 0.83 (95% CI 0.77, 0.89) for full-length S-binding IgG levels and 0.89–1.00 (lower bound of all 95% CIs > 0.67) for the four influenza strain-specific HAI titers, with all endpoints achieving the prespecified noninferiority criterion. Reactogenicity events were mostly mild or moderate when BNT162b2 was coadministered with SIIV. Serious AEs were reported in