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Two poxvirus-vectored vaccines for Japanese encephalitis (JE), NYVAC-JEV and ALVAC-JEV, were evaluated in rhesus monkeys for safety, immunogenicity, and protective efficacy. The vaccines were given to four monkeys each on study days 0 and 28 along with saline placebo on day 7. For controls, the licensed BIKEN JE vaccine and a saline placebo were given to other groups of four monkeys on days 0, 7, and 28. No systemic effects were observed. All injection site reactions were mild. All vaccines elicited appreciable JE-specific neutralizing antibody responses. However, a more rapid increase and higher peak level of antibody were seen in the BIKEN group as compared with the NYVAC-JEV and ALVAC-JEV groups. The peak neutralizing antibody level in the NYVAC-JEV group was higher than that of the ALVAC-JEV group. Antibody persisted in all four BIKEN recipients through 273 days of follow-up, whereas, the antibody level decreased to the threshold of detection in two NYVAC-JEV and all four ALVAC-JEV recipients by day 120. On day 273, all monkeys were given a booster dose. A rapid increase in neutralizing antibody was seen in all vaccine recipients by seven days. Two months after the booster dose, all monkeys were challenged intranasally with one 90% effective dose of JE virus. Four recipients of saline, three of ALVAC-JEV, one of NYVAC-JEV, and one of BIKEN experienced encephalitis. This study suggests that the NYVAC-JEV and ALVAC-JEV vaccines are safe and immunogenic in monkeys and that the NYVAC-JEV and BIKEN vaccines are effective in protecting monkeys from encephalitis.