Long-term immunogenicity and safety of the HPV-16/18 AS04-adjuvanted vaccine in 10- to 14-year-old girls: open 6-year follow-up of an initial observer-blinded, randomized trial.

Background: Immunogenicity and safety of the HPV-16/18 AS04-adjuvanted vaccine were evaluated up to 6 years postvaccination (month 72) in preteen/adolescent girls.
Methods: Participants, who had received 3 HPV-16/18 AS04-adjuvanted vaccine doses at 10-14 years of age in an initial controlled, observer-blinded, randomized study (NCT00196924) and participated in the open 3-year follow-up (NCT00316706), were invited to continue the follow-up for up to 10 years postvaccination (NCT00877877). Anti-HPV-16 and -18 antibody titers were measured by enzyme-linked immunosorbent assays at yearly visits and were used to fit the modified power-law and piecewise models, predicting long-term immunogenicity. Serious adverse events (SAEs) and pregnancy information were recorded.
Results: In the according-to-protocol immunogenicity cohort, all participants (N = 505) with data available remained seropositive for anti-HPV-16 and -18 antibodies at month 72. In initially seronegative participants, anti-HPV-16 and -18 antibody geometric mean titers were 65.8- and 33.0-fold higher than those associated with natural infection (NCT00122681) and 5.0- and 2.5-fold higher than those measured at month 69-74 in a study demonstrating vaccine efficacy in women aged 15-25 years (NCT00120848). Exploratory antibody modeling, based on the 6-year data, predicted that vaccine-induced population anti-HPV-16 and -18 antibody geometric mean titers would remain above those associated with natural infection for at least 20 years postvaccination. The HPV-16/18 AS04-adjuvanted vaccine safety profile was clinically acceptable.
Conclusions: In preteen/adolescent girls, the HPV-16/18 AS04-adjuvanted vaccine induced high anti-HPV-16 and -18 antibody levels up to 6 years postvaccination, which were predicted to remain above those induced by natural infection for at least 20 years.