The results obtained in the study of the antigenic activity and epidemiological effectiveness of live
parotitis vaccine prepared from strain
L-3 are presented. Children aged 3-7 years were shown to react to the injection of this preparation by the moderate production of virus-
neutralizing antibodies (the percentage of persons with antibody titers of 1:8 and higher increased from 26.5 to 64.4). The most intensive antibody production was stimulated by the
vaccines containing 40,000 and 20,000 viral particles in 1 vaccination dose. In seropositive children no significant shift in the antibody content was observed irrespective of the batch of the
vaccine used. During 1 1/2 years of observation the morbidity rate of
epidemic parotitis among children immunized with live
parotitis vaccine was 6.9 times lower than among the unvaccinated children in the same groups and 8.8 times lower than among the children used as external control. The effectiveness rate of the
vaccine was on the average 85.4% and 88.6%. The
vaccines containing 40,000 and 20,000 HADU50 were found to have greater epidemiological effectiveness, while the epidemiological effectiveness of the
vaccine containing 5,000 HADU50 was somewhat less. The effect of vaccination depended not only on the dose of the
antigen and the initial state of the
vaccines, but also on the extent of the coverage of children with vaccination in organized groups.