A novel chimeric vaccine protects pigs from infection with Japanese encephalitis virus

Widespread infection with a rare genotype 4 (GIV) strain of Japanese encephalitis virus (JEV) throughout eastern Australia in 2022 created new threats to animal and public health. Extensive production losses were incurred by the reproductive impacts of JEV infection at piggeries. Further, as an amplifying host for JEV, there are broader One Health advantages in minimising JEV infection of pigs. A candidate vaccine for pigs was developed using a chimeric virus with the structural glycoprotein genes (prM and E) of the outbreak JEV strain (JEV _NSW/22 ) inserted into an insect-specific orthoflavivirus (Binjari virus - BinJV) genome backbone (BinJ/JEV _NSW/22 ). Vaccines prepared with adjuvants using purified chimeric virus or a non-purified, formalin-inactivated formulation, induced JEV-specific antibody responses in mice and pigs. No adverse effects of vaccine administration were observed in either species for either vaccine formulation when used with a prime and boost delivery 28 days apart. Ninety-four percent (17/18) of weaner pigs that received the inactivated vaccine were protected from challenge with 1 x 10 ^5.0 TCID ₅₀ of JEV _NSW/22 , as determined by testing for JEV in blood and tonsils by RT-qPCR and virus isolation. In contrast, all control animals (n = 9) became viraemic and harboured JEV in the tonsils. When adult sows (1.5 to 3 years of age) (n = 9) were given a double-dose of the inactivated vaccine, there were no adverse effects, and each animal produced JEV-specific neutralising antibodies. Hence, BinJ/JEV _NSW/22 appears to be a promising candidate vaccine for prevention of JEV infection in pigs and can be used live or inactivated at varying levels of purity to provide manufacturers with logistical options for commercial production of the vaccine.