JAMA Netw Open. 2025 Jun 2;8(6):e2514622. doi: 10.1001/jamanetworkopen.2025.14622.
ABSTRACT
IMPORTANCE: In 2023, new immunization strategies became available for preventing respiratory syncytial virus (RSV) hospitalizations in infants and older adults. Modeling studies to understand the population-level impact of their use are important for public health planning.
OBJECTIVE: To estimate the number of hospitalizations averted in 2023 to 2024 due to new RSV immunization strategies and provide scenario projections for future seasons.
DESIGN, SETTING, AND PARTICIPANTS: This decision analytical model examined RSV hospitalizations in King County, Washington, from October 7, 2023, through April 26, 2025. The population of King County was disaggregated into infants younger than 6 months, infants aged 6 to 11 months, children aged 1 to 4 years, children/adults aged 5 to 59 years, adults aged 60 to 74 years, and adults aged 75 years or older.
EXPOSURES: Respiratory syncytial virus vaccination for adults aged 60 years or older, maternal RSV vaccination, and long-acting monoclonal antibodies (nirsevimab) for infants younger than 8 months.
MAIN OUTCOMES AND MEASURES: The proportion of RSV hospitalizations averted in adults aged 60 years or older and infants younger than 1 year were estimated using an RSV transmission model calibrated to RSV hospitalizations.
RESULTS: The RSV transmission model simulated the population of King County, which includes approximately 2.3 million individuals, with 23 700 infants younger than 1 year and 446 500 adults aged 60 years or older. During the 2023 to 2024 RSV season, 21.2% of adults aged 60 to 74 years, 32.7% of adults aged 75 years or older, and 33.0% of infants were protected through active or passive immunization. A total of 125 (95% projection interval [PI], 77-192) RSV hospitalizations were averted, with most of the benefit observed in infants younger than 6 months (28.6% [95% PI, 26.9%-30.5%] reduction from baseline) and adults aged 75 years or older (14.8% [95% PI, 14.3%-15.5%] reduction from baseline). For the 2024 to 2025 season, optimistic scenarios of high immunization coverage (50% in older adults and 80% in infants) projected reductions of 29.8% (95% PI, 29.1%-30.8%) in adults aged 75 years or older and 68.8% (95% PI, 66.0%-71.7%) in infants younger than 6 months compared with a counterfactual scenario with no immunizations. Targeting infants eligible for catch-up doses of nirsevimab early in the season increased the proportion of RSV hospitalizations averted in infants aged 6 to 11 months from 31.7% (95% PI, 29.4%-33.9%) to 40.4% (95% PI, 39.0%-42.1%). If vaccine protection in adults aged 75 years or older waned by 50% in the second year after immunization, the proportion of RSV hospitalizations averted was projected to decrease to 22.2% (95% PI, 21.7%-23.0%).
CONCLUSIONS AND RELEVANCE: In this decision analytical model of RSV immunizations, the results suggest a modest reduction in RSV-diagnosed hospitalizations during the 2023 to 2024 season due to limited availability of immunization products, particularly for infants. A higher uptake earlier in the season may lead to substantial reductions in RSV hospitalizations in the 2024 to 2025 season.
PMID:40498487 | DOI:10.1001/jamanetworkopen.2025.14622
