Berenson AB, et al. - A cross-sectional survey is performed to investigate changes in prevalence of vaginal human papillomavirus (HPV) between 2009-2010 and 2013-2014 among both vaccinated and unvaccinated U.S. women. The decline in HPV infections among unvaccinated 18- to 26-year-old women recommends that young women in the United States are beginning to benefit from herd immunity resulting from the introduction of the HPV vaccine.