Vaccination against Viral Hepatitis A and B in Adults Aged over 40 Years - Antibody Persistence and Immune Memory

Study objective: Primary vaccination with combined vaccine against viral hepatitis A (VHA) and viral hepatitis B (VHB) induces higher anti-hepatitis B surface (anti-HBs) antibody responses and similar anti-hepatitis A virus (anti-HAV) antibody responses in adults aged over 40 years in comparison with concomitant monovalent vaccines against VHA and VHB. The objectives were to assess, in a clinical study, persistence of anti-HAV and anti-HBs antibodies in adults aged over 40 years four years after primary VHA/VHB vaccination and antibody response following a booster dose of the vaccine. Material and Methods: Five hundred and ninety-six subjects aged > 40 years were vaccinated with three doses of the combined VHA/VHB vaccine at Months 0, 1, 6 (HAB group) or with concomitant VHA and VHB vaccines at Months 0, 6 and 0, 1, 6 (ENG+HAV and HBVX+VAQ, respectively). Blood samples were collected one month following primary vaccination (Month 7) and then at one-year intervals for four years after the booster dose with the same vaccine as used for the primary vaccination. The anti-HBs and anti-HAV antibody levels were determined prior to the booster dose and at days 14 and 30 after the booster dose. Results: At Month 7, > 97 % of study subjects were seropositive for anti-HAV antibodies in all groups analyzed. Four years after primary vaccination, anti-HAV antibody seropositivity persisted in > 93 % of study subjects, increasing to > 99 % after the booster dose. At Month 7, the highest proportion of study subjects with anti-HBs antibody levels >= 10 mIU/ml was found in the HAB group (91.7 % versus 79.7 % in the ENG+HAV group versus 71.0 % in the HBVX+VAQ group). Four years after vaccination, anti-HBs antibody levels of 10 mIU/ml persisted in 57.1 % of the HAB study subjects in comparison with 40.1 % and 26.6 % of the study subjects in the ENG+HAV and HBVX+VAQ groups, respectively. One month after the booster dose, anti-HBs antibody levels increased and antibody levels >= 10 mIU/ml was achived in 95.2 % of study subjects in the HAB group, 90.5 % in the ENG+HAV group and 85.3 % in the HBVX+VAQ group. Conclusion: In the adults aged over 40 years, an adequate anti-HAV antibody response persisted for at least four years after vaccination and was higher and more sustained in those who received the combined HAB vaccine. A strong antibody response to the booster dose indicative of the presence of immune memory was seen in all study groups.