A reduced national incidence of anogenital warts in young Danish men and women after introduction of a national quadrivalent human papillomavirus vaccination programme for young women--an ecological study.

In January 2009 the human papillomavirus (HPV) vaccine was included in the Danish childhood vaccination programme for girls aged 12 years. A catch-up programme for girls up to 16 years of age was started a couple of months earlier. Based on national register data, anogenital wart (AGW) incidences between January 2001 and December 2011 were estimated. We used χ2 analysis to identify significant trends in proportions of patients diagnosed with AGW in the period before and after inclusion of the HPV vaccine in the program. The development of chlamydia infections was included in this study as a proxy for possible behaviour changes that could affect the AGW incidence. Between 2008 and 2011, a 50% (95% CI 44-56) decrease in AGW incidence was seen among 15-19-year-old men (p = 0.041), from 5.2 to 2.6/1,000. Among women, a 67% (95% CI 63-72) decrease from 11.7 to 3.8/1,000 was seen (p < 0.0001). The decline in frequency of AGW in young Danish women seems to result from the high coverage of the HPV vaccination programme and young men probably benefit from herd immunity.