Respiratory Syncytial Virus Vaccine Effectiveness Among US Older Adults, 2023-2024 Season

Importance: Respiratory syncytial virus (RSV) causes a substantial number of hospitalizations and deaths among older adults. Two RSV vaccines for individuals aged 60 years or older were approved in 2023; it was important to monitor their clinical effectiveness during routine care in the first RSV season after regulatory approval. Objective: To estimate the clinical effectiveness of RSV vaccines during routine care overall and by brand among US older adults. Design, Setting, and Participants: This nationally representative, retrospective cohort study evaluated the effectiveness of RSV vaccines from August 6, 2023, to March 2, 2024. The primary analysis included eligible Medicare fee-for-service beneficiaries aged 65 years or older. Exposures: The RSVPreF3+AS01 RSV vaccine (GSK) and RSVpreF RSV vaccine (Pfizer). Main Outcomes and Measures: RSV-related hospitalization and RSV-related death. Results: Among 14 819 226 unvaccinated beneficiaries at the beginning of the study, the median age was 74 years (IQR, 70-79 years) and 57.7% were female. By the study end date, 13.9% of beneficiaries had received a RSVPreF3+AS01 vaccine, and 6.4% received a RSVpreF vaccine. Compared with the unvaccinated cohort, vaccinated individuals were less likely to have low-income status, lived in more affluent areas, and were more likely to have prior influenza vaccination and prior COVID-19 vaccination. The RSVPreF3+AS01 and RSVpreF vaccinated cohorts were largely comparable in demographic, social, and medical characteristics. Overall estimated vaccine effectiveness compared with the unvaccinated cohort was 81.8% (95% CI, 80.0%-83.4%) against RSV-related hospitalization and 85.0% (95% CI, 75.1%-90.9%) against RSV-related death. Brand-specific vaccine effectiveness against RSV-related hospitalization was 79.9% (95% CI, 77.6%-81.9%) for RSVPreF3+AS01 and 85.1% (95% CI, 82.2%-87.5%) for RSVpreF compared with the unvaccinated cohort. Vaccine effectiveness against RSV-related hospitalization was 72.2% (95% CI, 67.4%-76.3%) for immunocompromised individuals. Effectiveness did not change significantly with age. Conclusions and Relevance: In this cohort study of US older adults, both RSVPreF3+AS01 and RSVpreF vaccines had high effectiveness against RSV-related hospitalization and death during the 2023-2024 season. RSV vaccines demonstrated substantial effectiveness within this high-risk older adult population, including among immunocompromised individuals and across all ages 65 years or older. This large postmarketing noninterventional study provides clinical evidence of RSV vaccine effectiveness in the first year of vaccine approval.