Nirsevimab effectiveness on paediatric emergency visits for RSV bronchiolitis: a test-negative design study.

Abstract

Bronchiolitis is one of the leading reasons for paediatric emergency department (PED) visits. France was one of the few countries in the world to implement nirsevimab during winter 2023-2024 in order to reduce the burden of bronchiolitis each year. We conducted a test-negative design study, including all infants younger than 1, diagnosed with a first episode of bronchiolitis. We included all cases presenting to the PED of five university hospitals across France, between October 1, 2023, and February 29, 2024, and undergoing a nasopharyngeal sample for RSV testing. Case patients were the RSV-positive bronchiolitis and control patients the RSV-negative. As a follow-up, all parents were contacted by e-mail 15 days after inclusion. We included 383 bronchiolitis patients, of which 274 tested positive for RSV (75.2%). Among case patients, 27/274 (9.8%) received nirsevimab, compared to 50/109 (46.2%) among control patients. Nirsevimab had an adjusted estimated effectiveness of 82.5% (95% CI [68.0-90.8]) at PEDs. Sensitivity analyses found similar results. At 15-day follow-up, characteristics were similar between children immunized by nirsevimab or not.

Conclusion: Our findings advocate for nirsevimab widespread adoption to alleviate the burden of RSV bronchiolitis in paediatric emergency departments.

Trial registration: NCT04743609 (date of registration: February 4, 2021).

What is known: • Each year, RSV-bronchiolitis places significant pressure on pediatric emergency services. • France is one of the first countries in the world to have implemented nirsevimab in septembre 2023.

What is new: • Nirsevimab effectiveness on pediatric emergency visits for RSV-bronchiolitis has been estimated to 82.5% (95% CI [68.0-90.8]) in our study. • The effectiveness was as strong to prevent hospitalizations and sever illnesses.