TOPLINE:

The use of both nirsevimab in infants and maternal respiratory syncytial virus (RSV) prefusion F protein (RSVpreF) vaccine was associated with a more than 40% reduction in the burden of RSV-related hospitalizations and emergency department (ED) visits among infants aged 7 months or younger in Washington state during the 2024-2025 respiratory season.

METHODOLOGY:

• Researchers conducted a cohort study using surveillance data to assess the population-level impact of nirsevimab introduction among infants and maternal RSVpreF vaccination on RSV-related hospitalizations and ED visits among children aged 24 months or younger.
• The analysis included 16,775 children (median age, 10 months; 55% boys) with RSV-related hospitalizations or ED visits from July 2022 to June 2025.
• Infants aged 7 months or younger (n = 6840) served as the treatment group as they were eligible for nirsevimab or indirect protection from maternal vaccination, whereas children aged 8-24 months served as the comparison group (n = 9935).
• The study estimated mean relative changes in rates of RSV-related hospitalizations and ED visits for the treatment group beyond changes observed in the comparison group, before and after the introduction of RSV prevention products.
• Relative changes were estimated separately for the postvaccine respiratory seasons (July 2023 to June 2024 and July 2024 to June 2025) compared with the prevaccine respiratory season (July 2022 to June 2023).

TAKEAWAY:

• During the second postvaccine season (2024-2025), the estimated relative rate of RSV-related hospitalizations and ED visits among children aged 7 months or younger declined by an average of 43% beyond the change estimated for children aged 8-24 months (relative rate, 0.57; 95% CI, 0.48-0.68 ).
• The median age of children with RSV-related hospitalizations and ED visits increased from 9 months in 2022-2023 to 12 months in 2024-2025, suggesting a shift in disease burden toward older children.
• In the first postvaccine season (2023-2024), no statistically significant relative decrease in rates of RSV-related hospitalizations and ED visits was observed among children aged 7 months or younger.
• Relative changes were similar across racial groups except for children belonging to the Native Hawaiian or Other Pacific Islander race.

IN PRACTICE:

“Our data support continued use of long-acting infant monoclonal antibodies and antenatal vaccine in the state. Increased coverage of these products will likely be associated with additional decreases in severe disease burden for infants aged 7 months or younger, particularly in populations at increased risk,” the authors wrote.

SOURCE:

This study was led by Julia C. Bennett, PhD, Washington State Department of Health, Shoreline, Washington. It was published online on April 8, 2026, in JAMA Network Open.

LIMITATIONS:

Cases were identified using diagnostic codes rather than laboratory confirmation. Data on race and ethnicity were retrieved from medical records, and the method of ascertainment is unknown. Because nirsevimab is recommended for some high-risk children aged 8-19 months, some children in the comparison group may have received it, which could have biased the observed difference between groups.

DISCLOSURES:

No specific funding was explicitly mentioned in the article. One author disclosed receiving grants from the US Department of Health and Human Services/CDC, and another author disclosed receiving institutional support or personal fees from various pharmaceutical companies.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.