Impact of nirsevimab universal prophylaxis on RSV bronchiolitis hospitalizations. A tertiary level children's hospital perspective

Introduction: The 2024-2025 winter season was the first in which Nirsevimab was adopted as universal prophylaxis for bronchiolitis in Friuli Venezia Giulia, a region in the northeastern Italy. This report describes the impact of Nirsevimab universal prophylaxis on bronchiolitis from the perspective of a tertiary-level, children's hospital, the Institute IRCCS Burlo Garofolo in Trieste, Italy. Methods: We conducted a retrospective observational study reviewing the medical records of all children diagnosed with bronchiolitis during the 2024-2025 winter season, and the winter seasons of the seven preceding years. For each infant admitted, we collected data on age, gender, viral testing result, the need for ventilatory support, and the length of hospital stay. The primary outcome was the number of infant admissions for bronchiolitis during the 2024-2025 winter season, compared with previous years. Results: During the study period, from 2016 to 2025, 695 infants were diagnosed with bronchiolitis, and 195 were hospitalized. In the 2024-2025 winter season, 597 neonates, 94% of the children born at the Institute, received Nirsevimab prophylaxis. Following the introduction of Nirsevimab, we observed a drastic decrease in the number of infants requiring hospitalization, a marked reduction in infants needing ventilatory support, and a considerable decrease in the cumulative length of hospital stay for bronchiolitis, compared to previous years. These results were clearly related to a substantial decrease in the number of RSV-positive infants arrived at the Institute. Discussion: In our population, Nirsevimab prophylaxis was very effective and led to a considerable reduction in the number of infants infected with RSV and requiring hospitalization. The hospital burden of bronchiolitis was significantly reduced.