# The Impact of Nirsevimab on the Transport of Critically Ill Children

## TL;DR

A new drug called nirsevimab reduced the need to transport critically ill infants with respiratory infections, especially those caused by RSV.

## Contribution

Nirsevimab immunization significantly reduced bronchiolitis-related transports without affecting disease severity.

## Key findings

- Nirsevimab was associated with a 56% decrease in bronchiolitis transports among infants.
- RSV detection dropped from 74.3% to 47.4% after nirsevimab introduction.
- Other viruses like rhinovirus increased in post-nirsevimab cases.

## Abstract

What is known about this subject?
Respiratory syncytial virus (RSV)-positive bronchiolitis is the leading cause of interfacility transport in children <1 year, especially in winter.In October 2023, universal immunization against RSV in children under 6 months of age was started in Spain.

Respiratory syncytial virus (RSV)-positive bronchiolitis is the leading cause of interfacility transport in children <1 year, especially in winter.

In October 2023, universal immunization against RSV in children under 6 months of age was started in Spain.

What does this study add?
Immunization with nirsevimab was associated with lower rates of bronchiolitis requiring specialized transport in pediatric patients, particularly in RSV-related cases, without modifying disease severity among those requiring transfer.

Immunization with nirsevimab was associated with lower rates of bronchiolitis requiring specialized transport in pediatric patients, particularly in RSV-related cases, without modifying disease severity among those requiring transfer.

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.