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Quadrivalent human papillomavirus vaccination in girls and the risk of autoimmune disorders: the Ontario Grade 8 HPV Vaccine Cohort Study

Liu EY, Smith LM, Ellis AK, Whitaker H, Law B, Kwong JC, Farrington P, Lévesque LE. CMAJ. 2018; 190(21):E648-55. Epub 2018 May 28.

Background — Despite demonstrated effectiveness in real-world settings, concerns persist regarding the safety of the quadrivalent human papillomavirus (HPV4) vaccine. We sought to assess the risk of autoimmune disorders following HPV4 vaccination among grade 8 girls eligible for Ontario’s school-based HPV vaccination program.

Methods — We undertook a population based retrospective cohort study using Ontario’s administrative health and vaccination databases from 2007 to 2013.The self-controlled case series method was used to compare the rate of a composite end point of autoimmune disorders diagnosed during days 7–60 post vaccination (“exposed” follow-up) to that at any other time (“unexposed”).The analysis was repeated to assess the effect of a history of immune-mediated diseases and time since vaccination. We also conducted an exploratory analysis of individual autoimmune disorders. Rate ratios and 95% confidence intervals(CIs) were estimated using conditional Poisson regression, adjusted for age, seasonality, concomitant vaccinations and infections.

Results — The study cohort consisted of 290 939 girls aged 12–17 years who were eligible for vaccination between 2007 and 2013. There was no significant risk for developing an autoimmune disorder following HPV4 vaccination (n = 681; rate ratio 1.12, 95% CI 0.85–1.47), and the association was unchanged by a history of immune-mediated disorders and time since vaccination. Exploratory analyses of individual autoimmune disorders found no significant risks, including for Bell palsy (n = 65; rate ratio 1.73,95% CI 0.77–3.89), optic neuritis (n = 67; rate ratio 1.57, 95% CI 0.74–3.33) and Graves disease (n = 47; rate ratio 1.55, 95% CI 0.92–2.63).

Interpretation — We did not observe an increased risk of autoimmune disorders following HPV4 vaccination among teenaged girls. These findings should reassure parents and health care providers.