Background: A phase 2 double-blind, controlled, randomized multicenter study with human papillomavirus (HPV)-16/18 AS04-adjuvanted vaccine is ongoing in healthy Japanese women aged 20 to 25 years. We assessed the vaccine efficacy in the event-triggered analysis.

Methods: Japanese women aged 20 to 25 years were randomly assigned to receive either HPV-16/18 AS04-adjuvanted (n = 519) or hepatitis A (n = 521) vaccine at 0, 1, and 6 months. The women were assessed for virological and cytological end points associated with HPV-16/18 in cervical specimens and for the vaccine safety and immunogenicity.

Results: The mean length of follow-up for women in the primary analysis for efficacy at the time of a prespecified event-triggered interim analysis was 13.6 months after the first vaccination. Vaccine efficacy against HPV-16/18 persistent infections (6-month definition) in the according-to-protocol cohort for efficacy was 100% (99% confidence interval, 20.5-100, P = 0.0037). At 6 months after the third dose of vaccine, geometric mean titers against HPV-16 and HPV-18 were 2899.3 and 1352.2 enzyme-linked immunosorbent assay units per milliliter, respectively, that is, 97- and 60-fold higher than geometric mean titers observed after natural infection. There were no clinically meaningful differences in safety between the HPV and control group.

Conclusions: The HPV-16/18 AS04-adjuvanted vaccine was as efficacious in Japan as in other countries and was generally safe and highly immunogenic in Japanese women.