The Antibody Response in Human Beings Inoculated with Japanese Encephalitis Vaccine, Chick Embryo Type

Abstract

Summary Japanese encephalitis vaccines which were prepared from infected mouse-brain or chick-embryo tissue, and were of adequate potency as measured by the standard mouse-protective test, were found to be equally effective in immunizing human beings when the vaccines were administered to soldiers in two doses of 2.0 ml each given four days apart. Approximately 30 per cent of the men developed neutralizing antibodies following immunizations with either vaccine. Human beings immunized with 3.0 ml of chick embryo vaccine given subcutaneously in doses of 1.0 ml on the first, seventh, and thirtieth day developed neutralizing antibody with twice the frequency obtained with the first schedule. Similar results were obtained in a small group of persons who received three intracutaneous injections of 0.1 ml each of vaccine over a period of a month. A recall dose of vaccine administered subcutaneously to eight persons one year after vaccination elicited a significant rise in neutralizing antibody in five cases. A recall dose of 0.1 ml injected intradermally into another group of eight previously vaccinated persons resulted in a marked rise in the serum neutralization index of all eight. Neutralizing antibodies which appeared following primary vaccination persisted for a year in six of fourteen individuals. Only one of the human volunteers receiving either vaccine by either schedule developed specific complement-fixing antibodies to Japanese encephalitis virus following primary vaccination. However, an appreciable number of soldiers had antibodies which reacted with antigen prepared from normal chick embryo. Complement-fixing antibodies to Japanese encephalitis virus appeared in low titer in the sera of about one third of the persons who were repeatedly vaccinated.