Impact of the first nirsevimab immunization campaign on RSV-related emergency department visits and hospitalizations in Quebec, Canada

ObjectivesDuring the 2024-2025 respiratory syncytial virus (RSV) season, a universal nirsevimab infant immunization program was implemented in the province of Quebec. We evaluated its population-level impact on RSV-related emergency department (ED) visits and hospitalizations in infants, using both active surveillance and administrative health data. MethodsStudy population included all Quebec children <18 years old. Incidence rates of RSV-confirmed hospitalizations (6 hospital-based active surveillance), RSV-associated hospitalizations and ED visits linked to a positive RSV test, and acute bronchiolitis ED visits (administrative databases) were measured for nirsevimab-eligible (0-5 months old) and non-eligible (6-11 months and 1-17 years old) age groups during the 2024-2025 season and compared to the previous seasons (varying lookback periods). Using difference-in-differences and observed versus expected approaches, pre-/post-intervention variations in 0-5-month-olds were adjusted for any time trends extending to non-targeted age groups. ResultsDecreases of 59% (95% CI: 49-70) and 66% (95% CI: 58-71) were observed in RSV-confirmed and RSV-associated hospitalizations, respectively. Acute bronchiolitis ED visits decreased by 35% (95% CI: 28-41), and RSV-associated ED visits, by 60% (95% CI: 56-65). This impact became noticeable approximately one week after expanding the campaign to all eligible infants. ED visits and hospitalizations were less frequent than expected (i.e. without nirsevimab) in 0-5-month-olds, across all indicators. Between 323 and 746 hospitalizations were possibly prevented. ConclusionThe 2024-2025 nirsevimab campaign was associated with a two-thirds reduction in RSV-related hospitalizations and RSV-associated ED visits in Quebec infants. ED visits for acute bronchiolitis were also reduced by a third.