Real-world effectiveness of nirsevimab against respiratory syncytial virus in pediatric practice: the Piemonitorab study

Background: Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections (LRTIs) in pediatric populations, resulting in a substantial burden of disease. Immunization with the monoclonal antibody nirsevimab has shown efficacy in preventing RSV infection and reducing disease severity. This study aimed to evaluate the real-world effectiveness of a universal nirsevimab prophylaxis program against RSV-related LRTIs in children in the Piedmont region, Italy. Methods: A prospective, multicenter, observational study was conducted in the Piedmont Region (Italy). The primary endpoints were to assess nirsevimab immunization coverage among eligible infants and the number of RSV-related emergency department (ED) visits and hospitalizations during the 2024–2025 RSV season (October 1, 2024 to March 31, 2025). Secondary endpoints included the occurrence of adverse events following nirsevimab administration and the frequency of severe RSV-related outcomes, including intensive care unit (ICU) admission, need for respiratory support, and antibiotic therapy. The outcomes observed during the 2024–2025 season were compared with those from the 2022–2023 and 2023–2024 seasons. Results: During the study period, nirsevimab was administered to 71.5% of the eligible infants. According to individual-level analyses restricted to the at-risk population, nirsevimab-immunized children had a significantly lower risk of RSV-related ED visits (RR 0.14, 95% CI 0.11–0.18), hospitalization (RR 0.15, 95% CI 0.11–0.20), respiratory support (RR 0.14, 95% CI 0.09–0.19), and antibiotic therapy (RR 0.08, 95% CI 0.02–0.28) than nonimmunized children did. The estimated nirsevimab effectiveness exceeded 80% for RSV-related ED visits, hospitalization, and respiratory support. Compared with the two previous RSV seasons, the 2024–2025 season presented a notable decrease in RSV-related healthcare utilization. Conclusion: Universal nirsevimab prophylaxis is associated with a substantial reduction in medically attended RSV-related LRTIs among infants experiencing their first RSV season, including fewer ED visits and a lower frequency of severe disease requiring hospitalizations, respiratory support, and antibiotic use.