RSV prevention strategies linked to fewer infant hospital visits

The introduction of infant nirsevimab and maternal respiratory syncytial virus (RSV) prefusion F vaccine was associated with a substantial reduction in RSV-related hospitalizations and emergency department (ED) visits among infants, according to a recent cohort study published in JAMA Network Open.¹ The findings provide early population-level evidence that combined immunization strategies may reduce severe RSV burden in the first months of life.

RSV remains a leading cause of hospitalization in infants, particularly during the first year of life.² The study suggests that broad uptake of both passive immunization with monoclonal antibodies and maternal vaccination may shift disease burden and reduce health care utilization in this high-risk population.¹

“This analysis seeks to estimate the combined population-level impact of infant nirsevimab and antenatal RSVpreF vaccine on the rate of RSV-associated hospitalizations and [ED] visits among infants in Washington state using syndromic surveillance data,” wrote investigators.

Population-level impact of RSV prevention strategies

Investigators conducted a controlled quasi-experimental cohort study using syndromic surveillance data from the Washington State Department of Health Rapid Health Information Network. The analysis included 16,775 RSV-associated hospitalizations and ED visits among children aged 24 months or younger between July 2022 and June 2025.

The study compared outcomes before and after the introduction of RSV prevention products in autumn 2023. Infants aged 7 months or younger served as the exposure group, as they were eligible for nirsevimab or indirect protection from maternal vaccination. Children aged 8 to 24 months were used as a comparison group. A difference-in-differences approach with negative binomial modeling was applied to estimate relative changes in RSV-associated health care utilization.

During the prevaccine 2022 to 2023 season, infants aged 7 months or younger had greater RSV-associated hospitalization and ED visit rates than older children, at 6.1 vs 3.8 per 100 population. By the 2024 to 2025 season, rates declined to 2.6 and 2.7 per 100 population, respectively, indicating convergence between age groups.

The primary finding showed a 43.0% relative reduction in RSV-associated hospitalizations and ED visits among infants aged 7 months or younger in 2024 to 2025 compared with 2022 to 2023, beyond reductions observed in older children (relative rate, 0.57; 95% CI, 0.48-0.68; P < .001).¹ No significant differential reduction was observed during the first postimplementation year.

Most cases in the data set were ED visits without admission, accounting for 81% of encounters. Acute bronchiolitis because of RSV was the most common diagnosis, representing 81% of cases.¹

Clinical implications and remaining gaps

The observed reduction aligns with prior estimates of individual-level effectiveness for nirsevimab and maternal RSV vaccination, both of which have demonstrated protection against RSV-associated hospitalization in infants. The current analysis extends those findings by suggesting a measurable population-level impact when both strategies are implemented concurrently.

Investigators also reported heterogeneity in outcomes. County-level reductions ranged from 15.5% to 57.7%, with some smaller counties showing imprecise estimates. Racial disparities persisted, with the greatest RSV-associated visit rates observed among Native Hawaiian or Other Pacific Islander children, followed by children of multiple or other races and Black children. Notably, the relative reduction in 2024 to 2025 was smaller in Native Hawaiian or Other Pacific Islander infants compared with White infants.

These findings highlight both the potential and limitations of current RSV prevention strategies. While overall burden decreased, unequal impact across populations suggests differences in access, uptake, or underlying risk factors that warrant further investigation.

“Our data support continued use of long-acting infant monoclonal antibodies and antenatal vaccine in the state,” wrote investigators.

References

1. Bennett JC, Bevers E, Chronister S, et al. RSV prevention products and severe RSV-associated disease among infants. JAMA Netw Open. 2026;9(4):e265695. doi:10.1001/jamanetworkopen.2026.5695
2. Hall CB, Weinberg GA, Iwane MK, et al. The burden of respiratory syncytial virus infection in young children. N Engl J Med. 2009;360(6):588-598. doi:10.1056/NEJMoa0804877