Exploration of the effect of human papillomavirus (HPV) vaccination in a cohort of pregnant women in Montreal, 2010-2016.

HPV vaccination efficacy has been shown in clinical trials but it is important to verify population level vaccine effectiveness (VE). We aimed to explore VE and herd effect using HPV infection data from a cohort study of Canadian pregnant women. We analyzed the baseline data of the HERITAGE study, which includes pregnant women recruited in Montreal between 2010-2012 and 2015-2016. Cervicovaginal samples self-collected in the first trimester were tested for 36 HPV types. Vaccination status was self-reported. VE and 95% confidence intervals (CI) were estimated by comparing the prevalence of HPV between vaccinated and unvaccinated women. Herd effect was explored by comparing HPV prevalence in unvaccinated women between the 2 recruitment periods. Adjusted ORs (95%CI) were estimated using exact logistic regression. The proportion of vaccinated women with at least one dose of 4vHPV was 7.5%. Although most of them were vaccinated after the onset of sexual activity, a high VE was found for HPV-16/18 (86.1% (95%CI: 15.0-99.7)). For HPV-6/11/16/18 and for HPV-31/33/45, VE was 61.9% (-23.5-92.6) and 57.0% (-47.7-92.0%), respectively. We also observed a non-statistically significant reduction in the prevalence of HPV-6/11/16/18 and HPV-31/33/45 among unvaccinated women recruited during the second recruitment period (adjusted OR: 0.8 (0.4-1.8) and 0.8 (0.3-1.7), respectively).