Coverage, Timing, Safety, and Determinants of Neonatal Intensive Care Unit Admission in Newborns Receiving Nirsevimab...

Background: Nirsevimab, a long-acting monoclonal antibody targeting respiratory syncytial virus (RSV), has recently been introduced as universal prophylaxis in newborns and infants. Although clinical trials have shown high efficacy and a favorable safety profile, real-world evidence remains limited. Objectives: Our Italian multicenter observational study included newborns eligible for nirsevimab prophylaxis during the 2025-2026 season and aimed to assess nirsevimab coverage, timing of administration, and short-term safety in routine clinical practice. The association between perinatal and environmental factors and neonatal intensive care unit (NICU) admission was also investigated, while RSV occurrence was evaluated as a descriptive and exploratory outcome. Methods: Eligible newborns were from four Italian hospitals during the 2025-2026 RSV season. We assessed nirsevimab coverage, timing of administration, RSV incidence, adverse events, and selected neonatal, perinatal, and maternal risk factors. Results: Among 1554 eligible newborns, 1462 received nirsevimab, corresponding to a coverage rate of 94.0%. The median age at administration was 3.0 days (IQR 2-6 days), with significantly delayed prophylaxis in preterm compared with term infants. During the observation period, two laboratory-confirmed RSV-associated bronchiolitis cases occurred, corresponding to a cumulative incidence of 0.13%. One case occurred in the immunized group and one in the non-immunized group. No adverse events following immunization were recorded. Conclusions: Nirsevimab prophylaxis achieved high coverage and showed a reassuring short-term safety profile in this real-world multicenter cohort. RSV infections were uncommon, and their very limited number prevents definitive conclusions regarding comparative effectiveness between immunized and non-immunized newborns. Prematurity was associated with delayed administration and greater need for intensive care, underscoring the importance of timely prophylaxis in vulnerable newborns.