Efficacy and Safety of Anti-Respiratory Syncytial Virus Monoclonal Antibody Nirsevimab in Neonates: A Real-World Monocentric Study

Background: RSV remains a leading cause of infant hospitalization worldwide, and the recently approved nirsevimab could represent an effective and safe prophylactic strategy to prevent severe infections in the general neonatal population. Objectives: We conducted a retrospective observational monocentric pilot study in a mixed preterm/term birth cohort to add real-world evidence of the efficacy and safety of nirsevimab in preventing severe RSV infection. Methods: We included a total of 2035 consecutive infants admitted to the Neonatal Unit, University Hospital “San Giovanni di Dio e Ruggi d’Aragona”, Salerno, Italy, from November 2024 to April 2025. We evaluated 30-day safety profiles and season-wide RSV infection rates, and the outcomes were also compared to newborns’ birth rate in the two previous seasons (2022–2023 and 2023–2024). Results: After the introduction of nirsevimab, a lower RSV infection rate was reported compared to previous seasons, and no adverse effects were observed. Compared to previous seasons, the clinical outcomes were more favorable, as only one unvaccinated neonate with RSV infection required invasive ventilation. Conclusions: In this real-world analysis, we demonstrated a good short-term safety profile of nirsevimab, as well as a potentially high efficacy in the general neonatal population with lower RSV infection incidence. However, future studies are needed to better assess its long-term safety and season-wide efficacy.