RSV prevention lowered severe infant RSV burden
In Washington, infant antibody plus pregnancy vaccination was linked to fewer respiratory syncytial virus–related hospital and emergency visits in infants by the second year of rollout.
*Difference-in-differences cohort (quasi-experimental); Level 2b (OCEBM).

Citation

Bennett JC, Bevers E, Chronister S, et al. RSV Prevention Products and Severe RSV-Associated Disease Among Infants. JAMA Network Open. 2026;9(4):e265695. doi:10.1001/jamanetworkopen.2026.5695

Background

In 2023, Washington began using a long-acting preventive antibody for infants and a respiratory syncytial virus vaccine during pregnancy. Population-level evidence on their combined impact has been limited.

Patients

Washington residents aged 24 months or younger with clinically diagnosed respiratory syncytial virus–associated hospitalizations or emergency department visits (July 1, 2022–June 30, 2025). Data from 2020–2022 were excluded due to disrupted, atypical trends.

Intervention

Introduction of infant preventive antibody and pregnancy respiratory syncytial virus vaccination (starting autumn 2023).

Control

Children aged 8 to 24 months (comparison group) and the pre-introduction season (July 2022–June 2023).

Outcome

Rate of respiratory syncytial virus–associated hospitalizations plus emergency department visits.

Follow-up Period

Two respiratory seasons after rollout: 2023–2024 and 2024–2025.

Results

Comparison (difference-in-differences) Rate ratio (95% confidence interval) Relative change
2024–2025 vs 2022–2023 (≤7 months vs 8–24 months) 0.57 (0.48 to 0.68) 43.0% decrease
In 2023–2024 (first, limited-use year), no additional decrease was detected for infants beyond trends in older children.

Limitations

Cases were identified from diagnosis codes, not lab confirmation, so misclassification is possible. The study used group-level data (not individual receipt), so causation cannot be proven. Some protection may have occurred in the comparison age group, which could underestimate benefit. Race data were incomplete or potentially misrecorded, and county estimates were imprecise in small counties.

Funding

Public health agency support; relevant industry relationships were disclosed by one author.

Clinical Application

Continue and expand infant antibody and pregnancy vaccination; expect fewer severe infant cases, while monitoring coverage gaps and outcomes in higher-risk communities.