Background: Inactivated hepatitis A vaccines are licensed with a vaccination schedule based on two injections of vaccine given at least 6 months apart.

Methods: Two vaccination schedules for the inactivated hepatitis A vaccine, AvaximTM (Pasteur Mérieux Connaught, Lyon, France), were compared in a monocentric, randomized, open trial. Two doses of the vaccine were given at intervals of either 6 months (0–6 month group) or 12 months (0–12 month group) to 96 adult volunteers. Anti-hepatitis A virus (HAV) antibody titers were determined in a blind fashion using the modified RIA (mRIA) HAVABTM assay. After excluding subjects with positive preimmunization anti-HAV titers and those with protocol deviations, both groups were still comparable by sex ratio and mean age.

Results: Four weeks (28 ± 4 days) after the first dose, the seroconversion (SC) rate of initially HAV-seronegative subjects (antibody titer < 20 mlU/mL) was 100% in the 0–6 month group and 96.9% in the 0–12 month group, with corresponding geometric mean titer (GMT) values (95% Cl) of 369 mlU/mL (274–497 mlU/mL) and 445 mlU/mL (292–679 mlU/mL), respectively. After 6 months, SC was obtained in all subjects, and the corresponding GMT values were 349 mlU/mL and 359 mlU/mL in the 0–6 month group and the 0–12 month group, respectively. Four weeks after the booster dose given at 6 months, a 14.5-fold rise in GMT was observed. In the 0–12 month group, anti-HAV GMT values decreased by only 20% from 6 months to 12 months with a pre-booster GMT value of 286 mlU/mL at the 12-month evaluation. Four weeks after the booster given at 12 months, a 22.5-fold rise in GMT was observed. Statistical analysis showed that the two vaccination schedules were comparable in their ability to boost antibody titers. Unsolicited reactions to vaccination were not different to those reported during earlier trials. Less than 12% of the vaccinees reported reactions after the first dose (11/93), or after the booster dose (11/92).

Conclusions: This trial demonstrated antibody persistence is excellent for at least 12 months after one dose of this vaccine, and that a booster may be given at any time between 6 and 12 months after primary immunization.