A 20-year study of incidence trends of anogenital warts in Denmark -population impact of human papillomavirus vaccination.

Abstract

Anogenital warts are caused by infection with low-risk human papillomavirus (HPV). In 2008/2009 and 2019, Denmark implemented HPV vaccination for girls and boys, respectively, in the childhood vaccination program. This study investigates HPV vaccine impact by estimating the pre- and post-vaccination incidence of anogenital warts. Information on anogenital warts diagnosed 2000-2022 was extracted from the National Patient Registry and the National Prescription Registry. Age-standardized- and age-specific incidence rates were calculated alongside estimated annual percentage change. Incidence rate ratios (IRRs) were estimated by comparing post-vaccination periods (2008-2012, 2013-2019, 2020-2022) with a pre-vaccination period (2005-2007). The incidence of anogenital warts decreased significantly after HPV vaccination was implemented. In the latest post-vaccine period (2020-2022), IRRs showed decreases of 95%, 87% and 35% in women aged 15-19, 20-29, and 30-39 years compared to the period 2005-2007. For men in the same age groups, similar trends were observed with decreases of 84%, 75% and 7%. Our study shows population-level decreases in incidence rates of anogenital warts in post-vaccine periods, especially in younger women, while cohorts not covered by HPV vaccination continued having increasing rates. Decreases in anogenital warts in younger men before implementation of gender-neutral vaccination, points to substantial herd effects.