[Results of a study of the pathogenesis of postvaccinal encephalitis]

The results of 10-year virological and immunological studies in patients with postvaccination encephalitis (PVE) developing after smallpox vaccination are analysed. Vaccinia virus was isolated from 23 (59%) out of 39 children in the acute stage of PVE and for a long period in the protracted course of the disease in 14 out of 24 from the cerebrospinal fluid in 15 out of 33 from the blood, in 8 out of 24 from the throat and in 4 out of 5 from the brain or spinal cord tissue. Examinations of 56 serum specimens from 36 children with PVE revealed considerable variations in the levels of virus-neutralizing antibodies (VNA): 6 had no VNA, while 10 children showed low titres (10-20). No cases of agammaglobulinemia were observed. Instances of defective immune response were found which was manifested by a delay in increasing levels of IgM and IgG in response to vaccination. Two children were shown to have a defective cellular immunity. It is concluded that vaccinia virus participates in the pathogenesis of PVE; realization of the pathogenic properties of the virus requires the proper conditions, the main of which appears to consist in the immunodeficient state. The analysis of the appurtenance of 342 children to blood groups of the ABO system did not confirm the dependence of the development of postvaccination complications upon the presence in the blood of the vaccinees of the A antigen or immunological advantages of persons having alpha-isoantibodies.