Strongly Decreased Risk of Genital Warts After Vaccination Against Human Papillomavirus: Nationwide Follow-up of Vaccinated and Unvaccinated Girls in Denmark

Background. A reduction in the incidence of genital warts (GWs) is one of the first markers of the effectiveness of vaccination against human papillomavirus (HPV) at the population level. The aim of this cohort study was to use individual information on HPV vaccination status to assess the effect on risk of GWs. Methods. Population-based registries were used to identify all girls in the birth cohorts 1989-1999 in Denmark, and information about HPV vaccination was obtained for the period 2006-2012. The cohort was linked to incident cases of GWs, and vaccinated and unvaccinated girls were compared using Cox proportional hazards models. Results. A total of 248 403 girls were vaccinated. The relative risk of GWs among girls who had received at least 1 dose of vaccine compared with unvaccinated girls was 0.12, 0.22, 0.25, and 0.62 for those born in 1995-1996, 1993-1994, 1991-1992, and 1989-1990, respectively (P for trend <.0001). No GWs occurred among vaccinated girls in the youngest birth cohort (1997-1999). Conclusions. The strong, highly significant reduction in the occurrence of GWs among vaccinated girls indicates an early and marked population effect of the national HPV vaccination program and may forecast a similar effect on cervical precancerous lesions.