Abstract
This randomized, partially-blind study (ClinicalTrials.gov registration number NCT00541970) evaluated the immunogenicity and safety of 2-dose (2D) schedules of the HPV-16/18 AS04-adjuvanted vaccine. Results to month (M) 24 have been reported previously and we now report data to M48 focusing on the licensed vaccine formulation (20 μg each of HPV-16 and -18 antigens) administered at M0,6 compared with the standard 3-dose (3D) schedule (M0,1,6). Healthy females (age stratified: 9-14, 15-19, 20-25 years) were randomized to receive 2D at M0,6 (n = 240) or 3D at M0,1,6 (n = 239). In the according-to-protocol immunogenicity cohort, all initially seronegative subjects seroconverted for HPV-16 and -18 antibodies and remained seropositive up to M48. For both HPV-16 and -18, geometric mean antibody titer (GMT) ratios (3D schedule in women aged 15-25 years divided by 2D schedule in girls aged 9-14 years) at M36 and M48 were close to 1, as they were at M7 when non-inferiority was demonstrated. The kinetics of HPV-16, -18, -31, and -45 antibody responses were similar for both groups and HPV-16 and -18 GMTs were substantially higher than natural infection titers. The vaccine had a clinically acceptable safety profile in both groups. In summary, antibody responses to a 2D M0,6 schedule of the licensed vaccine formulation in girls aged 9-14 years appeared comparable to the standard 3D schedule in women aged 15-25 years up to 4 years after first vaccination. A 2D schedule could facilitate implementation of HPV vaccination programs and improve vaccine coverage and series completion rates.