In this randomized, observer-blinded, phase 2/3 study, S-268019-b (n = 101), a recombinant spike protein vaccine, was analyzed for noninferiority versus BNT162b2 (n = 103), when given as a booster ≥6 months after 2-dose BNT162b2 regimen in Japanese adults without prior SARS-CoV-2 infection. Interim results showed noninferiority of S-268019-b versus BNT162b2 in co-primary endpoints for neutralizing antibodies on day 29: geometric mean titer (GMT) (124.97 versus 109.70; adjusted-GMT ratio [95% CI], 1.14 [0.94-1.39]; noninferiority P-value, <0.0001) and seroresponse rate (both 100%; noninferiority P-value, 0.0004). Both vaccines elicited anti-spike-protein immunoglobulin G antibodies, and produced T-cell response (n = 29/group) and neutralizing antibodies against Delta and Omicron pseudovirus and live virus variants (n = 24/group) in subgroups. Most participants reported low-grade reactogenicity on days 1-2, the most frequent being fatigue, fever, myalgia, and injection-site pain. No serious adverse events were reported. In conclusion, S-268019-b was safe and showed robust immunogenicity as a booster, supporting its use as COVID-19 booster vaccine.
Keywords: Booster; Clinical trial; Immunization; Neutralization test; Recombinant spike protein; SARS-CoV-2.
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