[Dynamic changes in the epidemiological patterns of measles in the People's Republic of Bulgaria after mass vaccination and revaccination].

The main epidemiological regularities of measles before vaccination (1960--1968) and at the stage of mass vaccination (1969--1977) were studied. The average annual incidence of measles has been reduced from 423.97 to 279.72 per 100,000, mortality from 0.56 to 0.10 0/0000, and lethality from 0.13% to 0.04%. The dynamical changes of postvaccination immunity were uneven: in 1969 vaccinations covered 30.67%, in 1970 28.82%, in 1971 64.09%, in 1972 53.38%, in 1973 59.61%, in 1974 67.53%, and in 1975 69.04%. The level of herd immunity in those years was lower than the optimal (45.35%, 43.97%, 67.71%, 68.13%, 74.65%, 83.25%, and 84.63%, respectively). In the first part of 1976 a general immunoprophylactic campaign was carried out including vaccination of the unvaccinated children born in 1963--1975 and revaccination of all those vaccinated one year before the campaign. Primary vaccination increased the coverage by 11.25%, and revaccination increased the portion of seropositive subjects by 5.2%. As a result, a sufficiently high level of general herd immunity has been achieved (1976--96.02%, 1977--96.10%) and the incidence decreased accordingly (1976--192.69 0/0000, 1977--9.17 0/0000).