Simultaneous active and passive immunization against hepatitis A studied in a population of travellers.

Three hundred travellers, seronegative for hepatitis A, were enrolled into this study to evaluate a new inactivated hepatitis A vaccine. Three injections, each containing at least 720 ELISA units, were administered intramuscularly at months 0, 1 and 6. The subjects were distributed into three groups: 100 received vaccine only; 100 received a single injection of immunoglobulin enriched in HAV antibody; and the 100 remaining travellers received the vaccine and immunoglobulin administered simultaneously with the first vaccine dose. In both vaccinated groups, the rate of seroconversion was found to be higher than 90% at month 1, reaching 100% and 97.8% at month 2 in groups 1 and 3, respectively, and 100% at month 7. In the group receiving both vaccine and immunoglobulin, antibody production was somewhat slower and the final titres were, on average, slightly lower than those obtained in the group with the vaccine alone (GMT 2488 and 3614 mIU ml-1 respectively; p = 0.02). The vaccine appeared to be highly immunogenic in all subjects and was also well tolerated. The slight inhibition of antibody production, induced by the concurrent administration of immunoglobulin, does not affect the overall protection afforded by the vaccine. We conclude that simultaneous active and passive hepatitis A immunizations can be recommended.