Kinetics of anti–human papillomavirus (HPV) 16 and anti–HPV-18 antibody responses in initially seronegative participants in the vaccine group of the according-to-protocol (ATP) immunogenicity month 7 cohort. The ATP immunogenicity cohort at month 7 was used for the months 0, 2, and 7 time points; the ATP immunogenicity cohort at month 12, for the month 12 time point. Natural infection indicates GMT in women who had cleared a natural infection [16]; plateau, GMT at plateau level (months 45–50) from a previous study in women aged 15–25 years, in which sustained protection with the HPV-16/18 AS04-adjuvanted vaccine was shown up to 6.4 years after first vaccination [18]. Abbreviations: CI, confidence interval; EU, enzyme-linked immunosorbent assay units.