Decline in pediatric respiratory syncytial virus hospitalizations following nirsevimab implementation: A multicenter, three-season observational study

OBJECTIVES: To describe the demographic characteristics and clinical outcomes of hospitalized children with RSV in Catalonia during the first two seasons after the implementation of nirsevimab compared to the preceding season. METHODS: This observational study included patients <18 years hospitalized across 12 Catalan hospitals during three RSV seasons: 2022-2023, 2023-2024, and 2024-2025. We collected demographic, clinical and microbiological data on patients with a laboratory-confirmed RSV-positive respiratory sample. RESULTS: RSV-associated hospitalizations among <6-month-olds declined by 66.7% and 77.6% in the 2023-2024 and 2024-2025 seasons, respectively, compared to the prenirsevimab season. This resulted in overall reductions of 40.8% and 28.4% across all age groups and an increase in patient median age (16.6 and 11.8 vs 4.8 months, P < 0.001). PICU admissions for under 6-month-olds decreased by 69.8% and 75.5%, with global declines of 49.2% and 44.1%. There was a slight rebound in hospitalizations in 2024-2025. Median hospital length of stay and respiratory support duration both decreased by one day between 2022-2023 and 2024-2025. The proportion of patients with preexisting conditions such as asthma increased significantly (32.1% and 38.6% vs 19.7%, P < 0.001). CONCLUSIONS: After implementing nirsevimab, there was a significant decrease in pediatric RSV-associated hospitalizations and PICU admissions, especially among under 6-month-olds. The increase in patient median age and preexisting conditions highlight the need for new preventive strategies for these at-risk groups.