The Risk of Serious Respiratory-Related Events Following Immunization with the Quadrivalent Human Papillomavirus (qHPV) Vaccine: The Ontario Grade 8 HPV Vaccine Cohort Study
Cheung, Melanie T.
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Background: The qHPV vaccine has the potential to significantly reduce the burden of HPV-related diseases, including cervical cancer. However, a recent systematic review of clinical trials has suggested that the risk of bronchospasm may be increased by this vaccine, and a large observational study has reported an increased risk of anaphylaxis. Objectives: To determine whether qHPV vaccination increases the risk of incident asthma, asthma exacerbation, and anaphylaxis. Methods: A population-based retrospective cohort of grade 8 girls eligible for Ontario’s HPV immunization program between 2007 and 2011 was identified using the province’s administrative health and immunization databases. Cohort members were followed from September 1st of their grade 8 year until their date of death or end of study (March 31st, 2012). The self-controlled case series method, a self-matched, case-based analysis was used to assess the effect of qHPV vaccination on the risk of SRREs, and rate ratios (RRs) and 95% confidence intervals for each outcome was estimated using conditional Poisson regression. Results: The cohort consisted of 125,575 girls with a mean age of 13.2 years, 57.7% of whom received at least one dose of the qHPV vaccine. During an average of 2.5 years of follow-up, 1473 cases of incident asthma, 901 of asthma exacerbation and 38 of anaphylaxis were identified. HPV vaccination was not associated with an increased risk of incident asthma or asthma exacerbation (RRadj 0.76, 95% CI 0.37-1.54 and RRadj 0.74, 95% CI 0.27-2.00, respectively), and these associations were unchanged by the presence of risk factors and time since vaccination. There was also no evidence of an increased risk of anaphylaxis following qHPV vaccination as demonstrated by an absence of cases of anaphylaxis occurring on the day of vaccination. Conclusions: This large, population-based study provides strong evidence that the qHPV vaccine does not increase the risk of developing or exacerbating asthma, and additional evidence for the lack of an increased risk of anaphylaxis in the younger populations targeted by HPV immunization programs. These findings add to the growing body of evidence on the safety of the qHPV vaccine.