Following two consecutive RSV seasons, nirsevimab immunization demonstrated significant protection against severe outcomes. The first season showed a substantial reduction in severe disease, and this protective effect continued into the second season without increasing the risk of severe illness.

The study calculated marginal risk differences and risk ratios (RR) with 95% confidence intervals (95%CI) to quantify the effectiveness of the immunization. These metrics confirmed the protective impact of nirsevimab across both seasons.

Following two consecutive RSV seasons, nirsevimab immunization demonstrated significant protection against severe outcomes. The first season showed a substantial reduction in severe disease, and this protective effect continued into the second season without increasing the risk of severe illness.

Key Findings

• Researchers used inverse probability-weighted Kaplan–Meier methods to estimate the cumulative incidences (CInc) of various RSV-related outcomes from October 2023 to mid-February 2025.
• Hospitalizations: Nirsevimab reduced hospital admissions due to RSV.
• Intensive Care: It also lowered the need for pediatric intensive care unit (PICU) admissions.
• Emergency & Primary Care: There was a decrease in emergency department (ED) visits for bronchiolitis, as well as fewer RSV infections and bronchiolitis cases reported in primary care.

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