No evidence for cross-protection of the HPV-16/18 vaccine against HPV-6/11 positivity in female STI clinic visitors

Objectives Data from a vaccine trial and from post-vaccine surveillance in the United Kingdom have suggested that the bivalent HPV-16/18 vaccine offers cross-protection against HPV-6/11 and protection against anogenital warts (AGW). We studied the effect of the bivalent vaccine on genital HPV-6/11 positivity and AGW in the Netherlands. Methods We included all vaccine-eligible women from the PASSYON study, a biennial cross-sectional study among 16- to 24-year-old sexually transmitted infection (STI) clinic attendants. Vaginal self-swabs were analyzed for type specific HPV and AGW were diagnosed at the STI-clinic. Prevalence of HPV-6 and/or HPV-11 and AGW were compared between self-reported vaccinated and unvaccinated women by log-binomial regression analysis, adjusted for demographics and risk behavior. Results Of the 1198 women included, 56% reported to be vaccinated at least once. Relative to unvaccinated women, the adjusted prevalence ratio (PR) for HPV-6/11 was 1.03 (95% confidence interval [CI] 0.74–1.43) for women vaccinated at least once. The crude PR for AGW was 0.67 (95% CI 0.22–2.07) for women vaccinated at least once. Adjustment did not change these results. Conclusions We observed no cross-protective effect of the bivalent vaccine on genital HPV-6/11 positivity and a non-significant partially protective effect on AGW