Immunological and epidemiological effectiveness of live poliomyelitis vaccine in the USSR.

In 1959 a total of 1 700 000 children up to 14-18 years old in the Latvian, Byelo-russian, Moldavian and Russian Republics of the USSR were given live poliovirus vaccine prepared from attenuated Sabin strains. The results show that the vaccine is highly effective and quite innocuous.The mean reduction in poliomyelitis incidence in the different republics varied from sixfold to tenfold, and among very young children (the age-group at greatest risk) was as high as 15-fold. In regions where live vaccine was administered to the bulk of the susceptible population under 14 years of age, it was found that the usual seasonal rise in poliomyelitis incidence did not take place, although it did occur in the unvaccinated control regions. The number of cases of paralytic poliomyelitis was negligible among vaccinated children but relatively high among children in potential or actual contact with them. This suggests that "blind" immunization of contacts by spread of the attenuated vaccine virus is irregular and unreliable, and the authors therefore recommend vaccination of the susceptible population on the widest possible scale in order gradually to eliminate the reservoir of pathogenic wild strains of poliovirus.The optimum immunization schedule appears to be a first inoculation with type-1 monovaccine, a second inoculation 4-6 weeks later with divaccine of types 2 and 3, and a third inoculation with trivaccine after a similar interval.