Significant Decrease in the Incidence of Genital Warts in Young Danish Women After Implementation of a National Human Papillomavirus Vaccination Program

Background: Approximately 90% of genital warts (GWs) are caused by human papillomavirus (HPV) types 6 and 11. Denmark has provided the quadrivalent HPV vaccine to all 12-year-old girls since 2009 and catch-up vaccination to girls up to 15 years since 2008, with up to 80% to 85% vaccine coverage. We determined the incidence of GWs in Denmark since 1996, focusing on the period after licensing of HPV vaccination (October 2006). Methods: From the Danish National Patient Register, we identified all hospitalizations and outpatient consultations for GWs between January 1995 and July 2011. Poisson regression was used to estimate average annual percentage changes. Results: The overall incidence of GWs in women increased significantly until 2007, followed by an average yearly decline of 3.1% (95% confidence interval [CI], -5.5 to -0.7). In men, the incidence increased by 6.2% per year from 2004 (95% CI, 4.6-7.8). Stratifying on age, a significant decline was seen only for young women, particularly those aged 16 to 17 years, in whom GWs were virtually eliminated (average annual percentage change, -45.3%; 95% CI, -55.8 to -33.3). The incidences of genital Chlamydia, syphilis, and gonorrhea were stable or increased during the study period. Conclusions: The incidence of GWs decreased substantially among women with high HPV vaccine coverage, pointing to the effect of the national HPV vaccination program.