The status of herd immunity to measles in Russia: A systematic review and meta-analysis of epidemiological studies

Introduction. The comprehensive assessment of the herd immunity to measles in Russia can be challenging, as Russian subject-related studies tend to focus on seroprevalence in various cohorts of different sizes. The systematic review and subsequent meta-analysis of different research findings increase the total number of observations and statistical significance of the studies, thus enhancing the reliability of conclusions.The purpose of the study is to assess the status of herd immunity to measles in Russia by analyzing the findings of studies published by Russian researchers. Materials and methods. The conducted systematic review and meta-analysis covered 13 Russian studies (the total number of the examined was 15,353, from birth to 79 years of age) published in 2011-2020 and addressing the assessment of herd immunity to measles in population of different regions in Russia.Results. It was found that the principal approach in all the studies was assessment of herd immunity through examination of adult people, including healthcare workers, with no regard for their vaccination history. The proportion of seronegative cases among young people (18-30 years) — 27.3% (95% CI 25.7-27.3%) and among children under 17 — 38.3% (95% CI 35.8-40.8%), who were born after the two-time vaccination had been included in the National Immunization Calendar, was larger than in older age groups — 19.8% (95% CI 17.8¬21.8%). The level of herd immunity among healthcare workers representing a decreed group — 84.5% (95% CI 83.7-85.3%) was higher than that of relatively healthy population — 75.4% (95% CI 74.1-76.6%), which can be explained by stricter vaccination requirements.Conclusion. The high proportion of seronegative cases among children and young adults of under 30 years of age is a risk factor associated with measles spread among the population and can be seen as the result of insufficient vaccination coverage.