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Genital infection with human papillomavirus (HPV) is the etiologic agent for almost all cervical cancers; approximately 70% of cases involve HPV type 16 or 18. High-grade cervical lesions often begin to develop within 2 years of HPV infection. To determine whether a quadrivalent HPV vaccine (Gardasil) could prevent cervical intraepithelial neoplasia (CIN), investigators conducted a phase 3 trial in more than 10,000 women (age range, 15–26).
Participants were randomized to receive three doses of vaccine or placebo at 0, 2, and 6 months and were followed for evidence of CIN for 2.9 years after the first vaccination. Among participants without evidence of past or present HPV infection on DNA and serologic testing at baseline, the vaccine provid…