Recombinant vaccine against hepatitis E: dose response and protection against heterologous challenge.

Thirty-two rhesus monkeys were used to evaluate the dose response of a recombinant HEV vaccine, and the efficacy of the vaccine based on the ORF2 protein of the Pakistani strain for pre- and post-exposure vaccination against intravenous challenge with homologous or heterologous virus was examined. Post-exposure vaccination did not protect animals against hepatitis. Although primates vaccinated twice with 50-microgram, 10-microgram, 2-microgram, or 0.4-microgram doses of the recombinant 55 kDa ORF-2 protein were infected, they were protected from hepatitis when they were challenged with very high doses of the homologous strain of HEV. Primates vaccinated twice with a 50 micrograms dose of the recombinant protein were protected from hepatitis after heterologous challenge with the Mexican strain, the strain of HEV most genetically distant from the Pakistani strain.