mRNA-1345 RSV Vaccine Associated With Lower RSV Illness in US Veterans

Researchers used Veterans Health Administration records to emulate four monthly sequential trials from October 2025 through January 2026. They matched 74,926 veterans who received one dose of mRNA-1345 with 286,425 unvaccinated individuals, weighted to represent an equivalent number of controls. The cohort had a median age of 73 years and was 91.3% male. Outcomes were assessed for up to 24 weeks, with documented RSV infection as the primary outcome and RSV-associated emergency department or urgent care visits and hospitalizations as secondary outcomes.

Estimated vaccine effectiveness was 60.3% (95% CI, 49.0%-70.4%) against documented infection, 60.2% (95% CI, 47.2%-71.5%) against emergency or urgent care encounters, and 81.8% (95% CI, 58.1%-99.9%) against hospitalization. Estimates against documented infection declined with age, from 82.9% (95% CI, 64.0%-96.7%) among adults aged 50 to 59 years to 28.6% (95% CI, −12.0% to 60.4%) among those aged 80 years or older. An active-comparator analysis produced similar estimates.

The findings provide real-world evidence of protection during one respiratory illness season, but the observational design cannot establish causality. Applicability may be limited by the predominantly older, male veteran population. The authors note that comparative studies are needed to assess the relative benefits of available RSV vaccines.