Immunogenicity and protective efficacy in mice of a formaldehyde-inactivated Indian strain of Japanese encephalitis virus grown in Vero cells

P20778, an Indian strain of Japanese encephalitis virus (JEV) obtained from Vellore in the Southern India, was grown in Vero cells cultured on microcarriers in a spinner flask. The virus was formalin-inactivated and its immunogenicity and protective efficacy in mice were tested in comparison with a commercially available vaccine. Our studies indicated that formalin-inactivated JEV P20778 induced high levels of protective immunity in mice. Virus inactivation with formalin at 22°C, which required shorter incubation period, was found to be as good or better to virus inactivation at 4°C for generating high titers of anti-JEV antibodies. Similarly, the 22°C-inactivated virus generated JEV neutralizing antibody titers as good or higher than those induced by the 4°C-inactivated virus. Thus, for the vaccine production, inactivation of JEV with formalin at 22°C would be a preferred method as it is faster and does not require cold room storage