Evaluation of the Risk of Inflammatory Bowel Disease after the HPV Vaccination in Primary Care in Spain: A Time-Varying Cohort Analysis of Around 390,000 Girls

Introduction A link between the human papillomavirus vaccination (HPVv) and inflammatory bowel disease (IBD) has been suggested. Objective We aimed to estimate the risk of IBD following HPVv compared with periods not exposed to the vaccines. Methods Primary healthcare records (Spanish Primary Care Database For Pharmacoepidemiological Research [BIFAP]) were used in a cohort study of girls in Spain aged 9-18 years between 2007 and 2016 free of IBD or HPVv at study entrance. During the follow-up to IBD diagnosis, time-varying HPVv exposure and confounders were assessed in Cox models to estimate the hazard ratio (HRs) of IBD in the 2 years after HPVv (exposed period) and thereafter (post-exposed) compared with the no exposure periods. In a post hoc analysis, we moved the IBD date back 30 days as a theoretical delay in diagnosis confirmation. Results The cohort comprised 388,669 girls; 154,174 of these received the HPVv, and 88 IBD cases occurred (55 non-exposed, 22 exposed [after first N = 6, second N = 2, or third N = 14 dose] and 11 in post-exposed periods). The adjusted HR was 1.66 (95% confidence interval [CI] 0.68-4.05) for exposed and 1.10 (95% CI 0.37-3.24) for post-exposed periods. The HR for the first dose was 3.94 (95% CI 1.19-13.02). No association was found for the second or third doses. Post hoc, the HR was 1.83 (95% CI 0.72-4.69) for exposed periods (N = 18), and 1.84 (95% CI 0.35-9.83; N = 2), 1.50 (95% CI 0.40-5.63; N = 4) and 1.98 (95% CI 0.71-5.49; N = 12) after the first, second and third doses, respectively. Conclusions This study did not show an increased risk of IBD following 2 years of HPVv exposure. However, an increased risk of IBD diagnosis was observed following the first vaccination dose (1-34 days), which is likely attributable to the clinical recommendation to vaccinate upon onset of IBD symptoms.