Although maximum reduction in the risk of genital warts (condylomata) was seen after 3 doses of human papillomavirus (HPV) vaccine, receipt of 2 vaccine doses was associated with considerable reduction in risk, particularly among women who were younger than 17 years at first vaccination, according to a study in the February 12 issue of JAMA.
HPV infection causes genital warts and cervical cancer, and HPV vaccine prevents both. The typical dose schedule requires 3 doses of vaccine, but small clinical trials have reported measures of vaccine efficacy with fewer than 3 doses. Although the primary goal of HPV vaccination programs is to prevent cervical cancer, genital warts related to HPV types 6 and 11 are prevented with a version of the vaccine and are the earliest measurable preventable disease outcome for the HPV vaccine, according to background information in the study.
Eva Herweijer, M.Sc., of the Karolinska Institutet, Stockholm, Sweden, and colleagues assessed the association between the number of doses of HPV vaccination and genital warts among females 10 to 24 years of age living in Sweden (n = 1,045,165) who were followed up between 2006 and 2010, using the Swedish nationwide population-based health data registers.
Among 20,383 new cases of genital warts, 322 occurred after receipt of at least 1 dose of the vaccine. The researchers found that maximum risk reductions were found after 3 doses, but 2 doses were also protective, although to a lesser extent; there was small difference in the number of cases prevented by 3 doses vs 2 doses.
The authors caution that this study does not account for HPV disease outcomes other than genital warts, and that more studies with longer follow-up are needed to assess if these observed reductions apply for cervical cancer.