Durability of RSV Prefusion F Vaccine Protection across Two RSV Seasons

BACKGROUND: Respiratory syncytial virus (RSV) is an important cause of hospitalization and death among older adults. Although first-season vaccine effectiveness against RSV-related hospitalization has been demonstrated for the bivalent RSV prefusion F protein-based vaccine (RSVpreF), data regarding the durability of protection beyond a single RSV season are lacking. METHODS: In a pragmatic, open-label trial with individual randomization, participants 60 years of age or older were assigned in a 1:1 ratio to receive RSVpreF vaccine or no vaccine during the 2024-2025 winter season. Participants were followed through the 2025-2026 winter season to evaluate protection across two consecutive RSV seasons after a single vaccine dose. The primary endpoint was RSV-related respiratory tract disease (RTD) hospitalization. Secondary endpoints included RSV-related and all-cause lower respiratory tract disease hospitalization, all-cause respiratory hospitalization, all-cause cardiorespiratory hospitalization, and all-cause mortality. RESULTS: Of 131,379 participants who underwent random assignment, 130,991 were included in the intention-to-treat population during the second season. During the second RSV season, the incidence rate of RSV-related RTD hospitalization was 0.11 events per 1000 person-years in the RSVpreF group and 0.25 events per 1000 person-years in the control group, corresponding to a vaccine effectiveness of 56.2% (95% confidence interval [CI], -12.4% to 84.8%), as compared with 83.3% (95% CI, 42.9%-96.9%) during the first season. Across both seasons, the corresponding incidence rates were 0.11 and 0.37 events per 1000 person-years in the RSVpreF and control groups, respectively, with a vaccine effectiveness of 70.6% (95% CI, 39.1%-87.0%). There was no apparent difference in all-cause respiratory and cardiorespiratory hospitalization outcomes in the second season among those randomly assigned to vaccine or no vaccine in the first season. CONCLUSIONS: Among adults 60 years of age or older, the RSVpreF vaccine was associated with a lower incidence of RSV-related respiratory tract disease during a second RSV season as compared to no vaccine. Vaccine effectiveness estimates appeared to be lower in the second season compared to the first. (Funded by Pfizer; ClinicalTrials.gov number, NCT06684743.).