Monitoring HPV Vaccine Impact: Early Results and Ongoing Challenges

same period (15.8%) and women from the prevaccine period (28.7%). Using the age-adjusted HPV prevalence ratio of vaccinated to unvaccinated women, the authors calculate a vaccine effectiveness of 73% against infection with any of the 4 vaccine types. Because the major benefit of HPV vaccination—prevention of cervical and other less common HPV-associated cancers—will not be evident for decades, a spectrum of intermediate outcomes are being monitored to assess the early impact of HPV vaccines. Although considered to be the simplest and earliest indicator of vaccine impact, a reduction in HPV vaccine type prevalence may not be sufficient to guide vaccine policy and practices. Therefore, in addition to ongoing HPV type prevalence monitoring, cancer and precancer outcomes as well as HPV-associated genital warts are also included in the monitoring portfolios of most high-income and some middleand low-income countries where quadrivalent vaccine is being used [2, 3]. Although this study is the first to