Efficacy of an inactivated hepatitis A vaccine in pre- and postexposure conditions in marmosets.

A two-part challenge study was done in marmoset monkeys to confirm the efficacy of an inactivated hepatitis A vaccine. In part 1 (preexposure), 7 marmosets received a single low dose of vaccine (360 ELISA units [EL.U.]) and were challenged orally with wild type hepatitis A virus (HAV) either 1 or 6 months later. In part 2 (postexposure), 8 marmosets were challenged orally with HAV and then half each were inoculated with a single dose of 360 or 1440 EL.U. of vaccine 2 days later. The suboptimal immune response elicited by the low vaccine dose in the preexposure group was sufficient to induce complete protection against oral challenge with heterologous HAV in all marmosets that had responded serologically. In the postexposure group, the 360-EL.U. dose of vaccine resulted in partial protection against hepatitis A disease, whereas the 1440-EL.U. dose of vaccine elicited complete protection against disease and virus excretion.