ABSTRACT 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.
Foley et al. (2026) studied this question.