HPV vaccines were licensed and recommended a decade ago to reduce individual- and population-prevalence of HPV, a necessary cause of cervical carcinogenesis. These vaccines were initially tested and approved in three-dose regimens. Vaccine uptake has been poor in many world regions, likely the consequence of high costs and the intensive infrastructure required for administering three doses over a six-month period. In time, serological data provided consistent evidence that two doses administered among adolescents at least six-months apart evoked immunological responses that were non-inferior compared to three doses among the 16-to 26-year-old women who experienced protection in clinical trials. Consequently, European and US authorities reduced the dosing recommendation for adolescents to two doses. Yet, the Costa Rica Vaccine Trial (CVT) and the PATRICIA trial, both of which tested the bivalent HPV vaccine, showed in post-hoc analyses similar vaccine efficacy over four years among women who received one, two and three doses of the HPV16/18 vaccine, and stable antibody responses; the CVT has recently extended these data to seven years. Additionally, the 36-month preliminary analysis of a post-licensure trial of the quadrivalent vaccine showed similar protection against cervical infection with HPV16/18 regardless of number of vaccine doses. In this talk, post-hoc data from phase 3 clinical trials on efficacy and immunogenicity of a single dose of the HPV vaccines will be discussed.
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