Effect of postexposure vaccination in a chimpanzee model of hepatitis A virus infection.

Passive transfer of antibodies to hepatitis A virus (HAV) in immune globulin (IG) effectively prevents hepatitis A when given after exposure, but does not provide lasting protection from infection. Hepatitis A vaccines have been shown to generate quickly levels of antibody equivalent to those found after IG administration. The effect of hepatitis A vaccine in preventing infection following fecal-oral exposure was evaluated in a chimpanzee model of HAV infection. Two animals were vaccinated 1 and 3 days, respectively following inoculation and two inoculated animals served as unprotected controls. Of the two immunized animals, one had no evidence of HAV infection, while the other had an attenuated infection with no evidence of virus shedding. These results suggest that while postexposure hepatitis A vaccination may be infection permissive, it attenuates disease expression and prevents virus shedding.