The Impact of Nirsevimab on the Transport of Critically Ill Children

Purpose: Respiratory syncytial virus-positive bronchiolitis continues to be the main diagnosis prompting transportation in children younger than one year of age. It represents approximately 15-20% of all services performed by a specialized pediatric transport team. In October 2023, an immunization program with nirsevimab, a monoclonal antibody against RSV, was started in Spain. The purpose of the present study is to describe how nirsevimab affects the rates of bronchiolitis managed by a pediatric team specialized in critical patient transport. Secondary objectives included describing and comparing the clinical aspects of the two cohorts-pre-nirsevimab (pre-n) and post-nirsevimab (post-n)-to quantify how immunization has modified the clinical phenotype of bronchiolitis. Methods: This is a descriptive and observational study. Patients with bronchiolitis transported by a specialized pediatric transport team between September 2021 and August 2025 were included. Demographic, clinical, and microbiological data were collected. The pre-n and post-n periods were compared. Results: From a total of 2347 interfacility transports conducted by the unit between 2021 and 2025, 463 (19.7%) involved bronchiolitis patients, all of whom were recruited: 307 in the pre-n period and 156 in the post-n. The median age was 2.5 months (IQR 1.3-5.7), and 55% were male. There was a significant decrease in bronchiolitis cases that required specialized transport between the two periods: 28.2% (307/1089) pre-n vs. 12.4% (156/1258) post-n (p < 0.001). RSV detection also declined (74.3% vs. 47.4%, p < 0.001), while other viruses increased significantly in the post-n period, including rhinovirus, metapneumovirus and bocavirus. Age at admission showed statistically significant differences across the two periods (2.2 vs. 3.4 months, p < 0.001). There were no differences in severity between the two periods in terms of respiratory and inotropic support and length of stay. No mortality was reported. Conclusions: Universal nirsevimab immunization was associated with a marked reduction in pediatric transports for bronchiolitis, particularly RSV-related cases, without modifying disease severity among those requiring transfer.