Immunization of Laboratory Workers with Purified Venezuelan Equine Encephalomyelitis Vaccine

Abstract

The occurrence of infection with the Venezuelan equine encephalomyelitis virus in two members of our laboratory staff and the reports of 24 other laboratory infections with the same virus indicate the exigency for the protective immunization of personnel having contact with this agent. A formalinized vaccine prepared from chick embryos infected with the Venezuelan virus and partially purified by differential high-speed centrifugation was used to immunize 20 laboratory workers who had not previously had contact with the agent. Following two injections of 1.0 ml amounts of vaccine, the majority developed appreciable amounts of specific neutralizing antibody and one-half of them developed detectable amounts of specific complement-fixing antibodies. A third injection of vaccine resulted in increased amounts of both neutralizing and complement-fixing antibodies in the majority of the group. The neutralization indices now ranged from 150 to 1,585,000 and the complement-fixation titers from 0 to 1/32. While there was a general correlation between the results of neutralization and complement-fixation tests there was no close relation between the levels of antibody as determined by the two methods. None of the 20 persons who received the present vaccine developed clinical signs of disease when they subsequently engaged in the large scale manufacture of Venezuelan equine encephalomyelitis vaccine.