Impact of Nirsevimab Implementation on the Mid-Term Burden of Bronchiolitis in the Outpatient Setting: Results from the Prospective OURSYN Study.

CONTEXT: Nirsevimab was implemented in Europe and the United States in September 2023. While its effectiveness in preventing respiratory syncytial virus (RSV)-bronchiolitis has been demonstrated by real-life studies, its impact on mid-term child health, quality of life, and parental absenteeism remains unstudied.

METHODS

Infants under 1-year with a first bronchiolitis episode were recruited through the OURSYN study involving 37 primary care pediatricians in France between 2021 and 2025 (pre-nirsevimab period: 02/2021-03/2023 and nirsevimab period: 09/2023-03/2025). RSV status was determined by antigenic nasopharyngeal testing. At day 15, parents reported symptoms, quality of life (PedsQL Infant), and work absenteeism. Their associations with (i) RSV status, (ii) period of inclusion, and (iii) nirsevimab immunization status among RSV-positive cases were assessed using multivariable logistic regression adjusted for confounders.

RESULTS

Among 1870 bronchiolitis cases included, 637 (34.0%) occurred during the nirsevimab period and 812 (43.4%) were RSV-related. Over the study period, at day 15, RSV-cases had more feeding difficulties (aOR = 1.41 [1.06-1.88]), longer daycare absence (4.7 vs. 3.2 days), and more parental absenteeism (aOR = 1.61 [0.99-2.62]) compared to RSV-negative. The proportion of RSV-cases decreased during the nirsevimab period compared with the pre-nirsevimab period (47.1% vs. 35.7% P < .001). Bronchiolitis cases recruited during this period had shorter daycare absences (3.2 vs. 4.3 days). Among RSV-cases, immunized infants had lower risk of persistent fever (aOR = 0.14 [0.01-0.79]).

CONCLUSION

This large prospective study provides the first evidence that the mid-term burden of RSV-bronchiolitis in infants may be reduced following the implementation of nirsevimab, with potential benefits for infant health, quality of life and parental absenteeism.