Effect of hepatitis A vaccination schedules on immune response.

An inactivated hepatitis A vaccine was given to 104 seronegative volunteers aged between 19 and 60 years according to two schedules: 0, 1 and 2 months or 0, 1 and 6 months. The vaccine was well tolerated and 97 and 100% of vaccinees developed a serum antibody response following a single and two doses of vaccine respectively. Geometric mean titres increased progressively after each dose; responses following the 0, 1, 6 month schedule were significantly higher at one year but, among those tested at two years, these differences were less marked. Vaccinees, when compared with naturally infected persons, developed poor or undetectable hepatitis-A-virus-specific immunoglobulin G and A antibody responses in saliva and parotid fluid. Such differences are, however, unlikely to affect the protective efficacy of the vaccine.