Background: In Phase II/III trials, administration of quadrivalent human papillomavirus (HPV) (types 6/11/16/18) L1 virus-like-particle vaccine was highly effective in preventing HPV6/11/16/18-related cervical intraepithelial neoplasia and non-invasive cervical cancer in women aged 16-26 years who were naive to these HPV types at enrollment. However, the makeup and extent of catch-up vaccination programs among young women is unclear, because a proportion of this population will likely already have been exposed to one or more vaccine-HPV-types. Objective: Herein we analyze baseline data from the quadrivalent HPV vaccine clinical trial program to investigate variables which may help shape catch-up vaccine implementation policies. Methods: Female adolescents and young adults aged 16-26 years were randomized into five clinical trials. Baseline data regarding demographics, sexual history, pregnancy history, and other characteristics were collected at enrollment. At the baseline gynecological examination during enrollment, specimens were obtained for Pap testing. Swabs of external genital, lateral vaginal, and cervical sites for HPV polymerase chain reaction (PCR) testing were taken, and serum samples were obtained for HPV serology testing. Regional analyses of data were conducted. Results: Overall, 72% of subjects enrolled worldwide were naïve by both serology and PCR to all four vaccine HPV types. Few subjects were seropositive and/or PCR positive for more than two vaccine-related HPV types. Of all subjects with HSIL at enrollment, 78% were positive to at least one vaccine-related HPV type at enrollment. Regional differences in HPV and STD prevalence were evident. Study limitations included under-representation of women with ≥4 sexual partners and possible underestimation of prior HPV exposure. Conclusions: Our findings demonstrate that sexually active 16-26 year-old women with ≤4 life time sex partners (LSP) in North America, Europe, Latin America, and Asia Pacific are generally naive to most or all types targeted by the quadrivalent HPV6/11/16/18 vaccine and that they are at subsequent risk for infection and disease caused by these types.
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