The use and safety of the quadrivalent HPV vaccine in Grade 8 girls in KFL&A
Smith, Leah Marie
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INTRODUCTION: Use of the quadrivalent human papillomavirus (HPV) vaccine through Ontario’s $117 million program has been low, reaching only half of the eligible population. Safety concerns have been identified as a major barrier to vaccine uptake. In order to maximize the benefits of this program, it is necessary to understand factors associated with vaccine use and address parental safety concerns. DESIGN: We conducted a population-based, retrospective cohort study of girls eligible for Ontario’s Grade 8 HPV vaccination program in 2007 and 2008 residing in the Kingston, Frontenac, Lennox and Addington (KFL&A) health region. METHODS: Using data from the province’s administrative databases, we described the patterns of use of the quadrivalent HPV vaccine, identified factors associated with this use, and assessed the vaccine’s safety with respect to the risk of autoimmune diseases. To assess vaccine use, cross-tabulations were used to determine the vaccination and adherence status of girls according to socio-demographic and clinical characteristics. Logistic regression was used to estimate the strength of these associations. To assess the risk of autoimmune diseases, we identified all new cases of selected autoimmune diseases diagnosed during study follow-up. Juvenile arthritis was the only condition for which there were sufficient cases to permit further analysis. Rate ratios for juvenile arthritis were estimated using a self-matched analysis. RESULTS: We identified a cohort of 2519 girls eligible for publicly funded HPV vaccination in KFL&A, 56.6% of whom received at least one dose of the HPV vaccine and 48.2% of whom received all three doses. Vaccinated and unvaccinated girls differed only on the basis of vaccination history, whereas adherers and non-adherers differed on the basis of socio-demographics. The risk of juvenile arthritis was more than four times higher in the 60 days following HPV vaccination than in other time periods (RR 4.33, 95% CI 1.36-13.73). This risk appeared to vary across time. CONCLUSION: The results of this thesis provide new evidence of an increased risk of juvenile arthritis following quadrivalent HPV vaccination in girls aged approximately 13-15 years. Moreover, it demonstrates differences between vaccinated and unvaccinated girls, as well as adherers and non-adherers that have potential policy implications.