Immunogenicity and safety of a SARS-CoV-2 recombinant vaccine S-268024 booster vaccination versus NVX-CoV2373: Interim results from a phase 3, multicenter, randomized, observer-blind, active-controlled study

BACKGROUND: S-268024 is a recombinant protein vaccine developed as a COVID-19 booster. METHODS: This randomized, observer-blind, phase 3 study enrolled previously vaccinated Japanese adults without a history of SARS-CoV-2 infection. The noninferiority of the immunogenicity of the S-268024 booster vaccination versus NVX-CoV2373 was assessed. RESULTS: The immunogenicity population included 733 (S-268024 group: n = 368; NVX-CoV2373 group: n = 365) of 734 randomized participants. The geometric mean titer (GMT) ratio (95% confidence interval [CI]) was 1.79 (1.52-2.12), and the difference in seroresponse rate (95% CI) of SARS-CoV-2 neutralizing antibody was 7.9% (1.3%-14.4%) on day 29. The lower limit of 95% CI exceeded prespecified margins, indicating noninferior immunogenicity of S-268024 versus NVX-CoV2373; superiority in GMT was also demonstrated. Treatment-related adverse events (AEs) were numerically higher with S-268024 (92.4%) than NVX-CoV2373 (77.5%), with no treatment-related deaths/serious AEs/AEs of special interest. CONCLUSIONS: Interim analyses established noninferiority and superiority of S-268024 to NVX-CoV2373 in immunogenicity, with an acceptable safety profile.