Recombinant vaccine against hepatitis E: duration of protective immunity in rhesus macaques.

Hepatitis E virus (HEV) is an enterically transmitted virus that causes acute hepatitis. A candidate vaccine containing recombinant HEV capsid protein (56kDa) expressed in insect cells was shown previously to be highly immunogenic when administered in two doses to rhesus monkeys and to protect them from hepatitis E when challenged with a large intravenous dose of homologous or heterologous HEV. In the present study, the effect of a third dose of the same vaccine lot was evaluated and more importantly, the duration of protection following two doses was determined. Rhesus monkeys vaccinated twice with the 56kDa capsid protein were challenged with homologous virus 6 or 12 months after the last vaccination: 3 of 4 monkeys challenged 6 or 12 months later, respectively were protected against viral hepatitis. Similarly, all four of the rhesus monkeys given a third dose of vaccine 1 month prior to challenge were protected against hepatitis. In contrast, all four monkeys given placebo developed hepatitis following challenge. In summary, two doses of HEV vaccine partially protected rhesus monkeys from hepatitis E following intravenous challenge 6 or 12 months after vaccination.