Is varicella vaccination associated with pediatric arterial ischemic stroke? A population-based cohort study

Abstract Background and purpose: Varicella disease is a risk factor for pediatric Arterial Ischemic Stroke (AIS). Isolated case reports have emerged suggesting that varicella vaccination may also pose a risk for AIS. Methods: This retrospective population-based cohort study assessed the risk of AIS in children who received a varicella-containing vaccine, as compared to those who did not. The study cohort consisted of children born between January 1, 2006 and December 31, 2013, in the Canadian province of Alberta, where all routine childhood vaccinations are publicly-funded, and recorded in a central immunization repository. These data were linked with hospital discharge abstract data to identify children diagnosed with AIS. A Cox proportional hazard model assessed the risk of AIS in the 12 months following vaccination for children receiving a varicella vaccine between 11 and 23 months of age, as compared to non-vaccinated children. Results: Of the 368,992 children in the cohort, 325,729 were vaccinated with a varicella-containing vaccine between 11 and 23 months of age. The rate of AIS was 7.8 (95% CI 4.8–10.9) per 100,000 person years at risk in the 12 months following varicella vaccination, as compared to 6.8 (95% CI 1.3–12.2) for children who did not receive a varicella vaccine. The adjusted Hazard Ratio for the risk of AIS, controlling for other AIS risk factors, in vaccinated children as compared to non-vaccinated children was 1.6 (95% CI 0.7–3.7) in the 12 months following vaccination and 1.7 (95% CI 0.5–4.9) in the 30 days following vaccination. Conclusions: Our study found no evidence of an increased risk of AIS following varicella vaccination. This population-based cohort study provides reassurance to parents and clinicians regarding the safety of varicella vaccination.