Vaccinia virus in postvaccinal encephalitis.

Results of virological examination of 239 samples taken from 84 children with neurological complications after smallpox vaccination are described. In postvaccinal encephalitis, vaccinia virus was isolated from blood, cerebrospinal fluid and pharyngeal secretions of 23 out of 40 children (57.5%) as well as from autopsy specimens sampled between 10-35 days after vaccination. During the acute period of disease, virus was detected in 17 out of 31 (54.2%) cerebrospinal fluid specimens. In 3 postvaccinal encephalitis cases the virus was present in brain and in a case of encephalomyelitis--in the spinal cord. These results confirmed the participation of vaccinia virus in the pathogenesis of postvaccinal encephalitis. The pathogenicity of vaccinia virus may be manifested only under a changed reactivity of the vaccinated host.