Long‐term persistence of immune response to the AS04‐adjuvanted HPV‐16/18 vaccine in Chinese girls aged 9‐17 years: Results from an 8‐9‐year follow‐up phase III open‐label study

AIM In 9-17-year-old Chinese girls, the AS04-adjuvanted HPV-16/18 vaccine (AS04-HPV-16/18) given as three-dose schedule induced high antibody levels, which were noninferior 1 month after the third dose to those observed in 18-25-year-old Chinese women in a large efficacy study. We assessed the persistence of antibodies 8-9 years after vaccination in the same subjects. METHODS This follow-up phase III, open-label study (NCT03355820) included subjects who had received three doses of AS04-HPV-16/18 in the initial trial (NCT00996125). Serum antibody concentrations were assessed by ELISA and compared to antibody persistence observed in 18-25-year-old Chinese women 6 years after first vaccination in the efficacy study (NCT00779766). RESULTS Out of the 227 enrolled subjects, 223 were included in the per-protocol immunogenicity analysis. Mean interval from first AS04-HPV-16/18 dose to blood sampling was 101.4 months (8.5 years). For antibodies against HPV-16 and -18, 8.5 years after first vaccine dose all subjects remained seropositive and antibody. Geometric mean concentrations (GMCs) were 1236.3 (95% confidence interval [CI]: 1121.8; 1362.4) and 535.6 (95% CI: 478.6; 599.4) ELISA Units/mL, respectively. These seropositivity rates and antibody GMCs were higher than those observed 6 years after first vaccination of 18-25-year-old women. CONCLUSION Sustained anti-HPV-16 and -18 immune responses were observed 8-9 years after AS04-HPV-16/18 vaccination of 9-17 year-old Chinese girls that were higher than the ones observed 6 years after first vaccination in Chinese adult women in whom AS04-HPV-16/18 efficacy against cervical intraepithelial neoplasia of grade ≥2 was demonstrated.