Persistence of immune responses to the HPV-16/18 AS04-adjuvanted vaccine in women aged 15–55 years and first-time modelling of antibody responses in mature women: results from an open-label 6–year follow-up study

OBJECTIVE Evaluation of the long-term HPV-16/18 AS04-adjuvanted vaccine immunogenicity persistence in women. DESIGN Multicentre, open-label, long-term follow-up (NCT00947115) of a primary phase-III study (NCT00196937). SETTING Six centres in Germany and Poland. POPULATION 488 healthy women (aged 15-55 years, age-stratified into groups: 15-25, 26-45, and 46-55 years) who received three vaccine doses in the primary study. METHODS Immune responses were evaluated in serum and cervicovaginal secretion (CVS) samples 6 years after dose 1. Anti-HPV-16/18 geometric mean titres (GMTs) were measured by enzyme-linked immunosorbent assay (ELISA), and were used to fit the modified power-law and piecewise models, predicting long-term immunogenicity. Serious adverse events (SAEs) were recorded. MAIN OUTCOME MEASURES Anti-HPV-16/18 seropositivity rates and GMTs 6 years after dose 1. RESULTS At 6 years after dose 1, all women were seropositive for anti-HPV-16 and ≥97% were seropositive for anti-HPV-18 antibodies. GMTs ranged from 277.7 to 1344.6 EU/ml, and from 97.6 to 438.2 EU/ml, for anti-HPV-16 and anti-HPV-18, respectively. In all age groups, GMTs were higher (anti-HPV-16, 9.3-45.1-fold; anti-HPV-18, 4.3-19.4-fold) than levels associated with natural infection (29.8 EU/ml). A strong correlation between serum and CVS anti-HPV-16/18 levels was observed, with correlation coefficients of 0.81-0.96 (anti-HPV-16) and 0.69-0.84 (anti-HPV-18). Exploratory modelling based on the 6-year data predicted vaccine-induced anti-HPV-16/18 levels above natural infection levels for at least 20 years, except for anti-HPV-18 in the older age group (piecewise model). One vaccine-related and two fatal SAEs were reported. CONCLUSIONS At 6 years after vaccination, immune responses induced by the HPV-16/18 AS04-adjuvanted vaccine were sustained in all age groups.