[Current problems in the epidemiology and prevention of measles in the Ukrainian SSR. Reasons for the unfavorable epidemic situation with respect to measles which developed during the years of planned immunization].

In the first years of specific mass immunization (1969--1971) the epidemic situation in the Ukrainian SSR was more favorable than during the following period (1976--1977). With time after immunization the protection of the vaccinees decreased. The main reason of the measles virus circulation, of regular epidemics and the aggravation of the epidemic situation in 1976 and 1977 was the presence of 10% of seronegative children, which amounts to more than a million children unprotected against measles in the republic, and the decrease of the immune stratum of the children who had led measles (who played a definite role in the suppression of the epidemic process in 1969--1971) from 40% to 12%.