Machalek DA, et al. - In this study, the impact of a quadrivalent human papillomavirus vaccination program on HPV prevalence among women aged 18–35 in 2015 was determined. This study reported the longest surveillance follow-up to date and showed a continuous decline in the prevalence of vaccine-targeted HPV types among young women. Despite lower coverage, women aged 25–35 also showed a substantial fall. These reductions could be due to strong herd protection, and the effectiveness of less than three-doses of the vaccine.