[Inactivated vaccine against Japanese encephalitis. The characteristics of a purified preparation from mouse brain].

A vaccine has been prepared from formalin-inactivated suspension of brain tissue of Japanese encephalitis (JE) virus-infected white mice. The material was purified by flow ultracentrifugation in sucrose density gradient. Four members of the Nakayama antigenic group were compared as production JE virus strains for the vaccine preparation. Satisfactory results with regard to the immunogenicity of the bulk vaccine determined in mice (the intensity of response and the antigenic spectrum range) were obtained for three of them, including only one of the two variants of the Nakayama NIH strain. The highly purified experimental vaccine proved to be immunologically active and safe in trials in laboratory animals and 20 human volunteers. After two vaccinations, immunological changes in people were recorded much more frequently in the neutralization test than in the hemagglutination-inhibition test. Blasttransformation of lymphocytes in response to the specific antigen was observed in 5 out of 7 vaccines examined. There was no strict correlation of this test with the results of both serological tests.