The NCI-sponsored Costa Rica Vaccine Trial (CVT) and the commercially-sponsored Papilloma TRIal against Cancer In young Adults (PATRICIA Trial), both of which tested the bivalent HPV vaccine, showed similar vaccine efficacy over four years among women who received one, two and three doses of the HPV16/18 vaccine, and stable antibody responses have been observed throughout the seven years of follow-up accrued to date in CVT, suggesting durability of responses. Additionally, 36-month preliminary analysis of a large, post-licensure trial of the quadrivalent vaccine in India showed similar protection against HPV16/18 cervical infection whether the women received one dose, two doses, or three doses. However, vaccine recipients in these trials were not randomized to receive these fewer doses, and immunogenicity among one-dose recipients was lower than that observed following two- or three-doses, leading regulatory bodies to conclude that the level of evidence in support of single-dose HPV vaccination is insufficient to warrant changes in current recommendations for two- or three- dose schedules.