Immunological aspects of features of post-vaccine immune response to measles virus are presented and causal relationships are detected, that lead to the disappearance of protective anti- bodies against measles virus, as one of the arguments for improvement of vaccination tactics with the aim to increase immune population and enhancement of epidemiologic situation regarding measles in general. At contemporary stage during mass vaccinations against measles a portion of seronegatives among women of reproductive age and newborns (up to 20.1%) with an additional increase of this parameter by 8 - 13% during pathologic course of pregnancy is established. At the age of 12 months portion of seronegatives among children with health deviations reaches 80 - 90.0% against 53.8% - in healthy. Revaccination of children with deviation of health is shown not to result in production of antibodies against measles virus at protective titers in 30.4 - 33.3% of cases, that could facilitate formation of risk groups for measles virus infection during unfavo- rable epidemic situations. A problem of possible introduction of a third dose of the measles vaccine. among the indicated population groups is discussed.