A Randomized Phase 3 Study to Evaluate the Safety, Tolerability, and Immunogenicity of the Bivalent RSVpreF Vaccine in Older Adults in Korea.

Background/Objectives: The bivalent RSVpreF vaccine is effective at preventing respiratory syncytial virus (RSV)-associated lower respiratory tract illness in adults. However, data regarding safety and immunogenicity of RSVpreF in Korean populations are limited. Methods: This was a phase 3, multicenter, placebo-controlled, randomized (2:1), double-blind study in Korean adults 60 years of age and older. Participants received a single 120-μg dose of RSVpreF or matching placebo. Safety endpoints included local reactions and systemic events through 7 days and adverse events (AEs) through 1 month after vaccination, and serious AEs (SAEs) throughout the study. RSV-A and RSV-B serum 50% neutralizing geometric mean titers (GMTs) and geometric mean fold rises (GMFRs) were obtained 1 month after vaccination. Results: Overall, 377 participants received study intervention (RSVpreF, n = 251; placebo, n = 126). Most local reactions and all systemic events were of mild or moderate severity. Injection-site pain was the most frequently reported local reaction (RSVpreF, 12.4%; placebo, 3.2%). The most frequently reported systemic events were fatigue (RSVpreF, 23.1%; placebo, 26.2%) and muscle pain (RSVpreF, 15.5%; placebo, 9.5%). AEs through 1 month after vaccination were infrequent (RSVpreF, 3.6%; placebo, 0.8%); none were considered vaccine related by the investigator. RSV-A and RSV-B neutralizing GMTs increased 1 month after RSVpreF, with GMFRs (95% CIs) from before to 1 month after vaccination of 9.5 (8.51-10.67) for RSV-A and 8.3 (7.37-9.39) for RSV-B. Conclusions: In older Korean adults, RSVpreF had an acceptable safety and tolerability profile and elicited robust RSV neutralizing responses 1 month after vaccination consistent with pivotal phase 3 efficacy trial results. ClincalTrials.gov Identifier: NCT06593587 (date of registration: 9 September 2024).