Background: Palivizumab was introduced in Canada in 1998 as a publicly funded programme to reduce respiratory syncytial virus (RSV) disease in high-risk children. Severe early-life RSV infections are associated with increased asthma risk. Thus, palivizumab may also indirectly reduce paediatric asthma.
Objective: To evaluate the effectiveness of Ontario, Canada's palivizumab programme in decreasing paediatric asthma.
Methods: We used multiple linked population-based administrative databases to identify all children born in Ontario between 1993 and 2013, with follow-up through March 2020. Our primary outcome was physician-diagnosed asthma by age 7. Controlled interrupted time-series analysis was used to compare changes in annual asthma incidence (by birth year) before and after palivizumab's introduction, according to programme eligibility (clearly, possibly, or ineligible). Socio-demographic differences were explored via stratification.
Results: Nearly 3 million children were included in this study, including 406,596 (14.6%) diagnosed with asthma by age 7. Asthma incidence substantially declined over the study period, with the greatest declines among palivizumab-ineligible children (35.3%, 95% confidence interval [CI] 28.3, 42.6, versus 18.1%, 95% CI 13.9, 22.9 among clearly eligible children). However, relative to ineligible children, post-palivizumab declines were most apparent among possibly eligible children, with an additional annual decline of 2.0% (95% CI 0.3, 3.7) in asthma. Socio demographic differences in asthma incidence and post-palivizumab declines were noted. Particularly, incidence was higher among children born to teenage mothers than among those aged 19+ years; this gap narrowed over time, especially among possibly eligible children.
Conclusions: Asthma incidence declined over this 20-year study; however, smaller declines were observed among children clearly eligible for palivizumab relative to ineligible children. However, exploratory evidence was suggestive of reduced social inequities in asthma post-palivizumab, particularly among possibly eligible children. Larger reductions in asthma might be realized with the introduction of population-based RSV immunization programmes through broader programme eligibility and reductions in severe RSV disease.
Keywords: asthma; child health; interrupted time series analysis; palivizumab; respiratory syncytial virus.
© 2026 The Author(s). Paediatric and Perinatal Epidemiology published by John Wiley & Sons Ltd.