Vaccine effectiveness of mRNA-1345 against RSV-associated hospitalization and medically attended acute respiratory illness among US veterans, 2025–2026

Background Clinical trials showed mRNA-1345 (mRESVIA) was highly efficacious against RSV-associated lower respiratory tract disease in adults; real-world studies are critical to confirm vaccine impact on RSV-related healthcare usage. Methods A retrospective test-negative case-control study used Veterans Health Administration electronic health records from the 2025–2026 respiratory season. Veterans aged ≥50 years with acute respiratory illness (ARI) who underwent RSV testing were included. Vaccine effectiveness (VE) of mRNA-1345 was estimated against RSV-positive ARI-associated hospitalization, urgent care/emergency department (UC/ED), and/or outpatient visits using conditional logistic regression. Results 1.4% of 91,397 tested persons received mRNA-1345. The matched analysis included 3673 RSV cases and 14,566 controls. Among RSV-positive ARI-associated hospitalizations, <5/649 cases and 49/2572 controls were vaccinated (VE: 85%[95% CI:39%–96%]). Effectiveness against medically attended RSV-ARI was 65%(45%–77%), 57%(28%–74%) against ED/UC visits and 71%(19%–90%) against outpatient visits. Conclusions mRNA-1345 is associated with substantial protection against RSV-positive ARI-associated hospitalization that was generally consistent across medically-attended outcomes.