Population immunity and structure of measles cases in the Russian Federation

Relevance. In recent years, in Russia, against the background of a stable high (no less than 95%) coverage of live measles vaccine (GI) inoculations of decreed groups of the population for almost twenty years, increases in morbidity have been registered, reaching the indicators of 3.3(2014) and 3.1 (2019) per 100 ths population and local outbreaks involving the child population. This situation has raised doubts among a number of researchers about the reliability of high vaccination coverage in children and adults. In this regard, some researchers assumed the loss of post-vaccination immunity and suggested revaccination against measles every 10 years for people up to 50 years old. Others suggested serological examination of certain cohorts of the adult population without taking into account the vaccination history for timely detection and vaccination of individuals with primary post-vaccination failures and who have lost post-vaccination immunity. The purpose of the work: to assess the state of population immunity for some manifestations of the epidemic process of measles infection and the feasibility of changing the tactics of vaccination against measles. Materials and methods. The work uses epidemiological operational and retrospective analysis. The research is based on the analysis of official statistics № 2, № 5, № 6, reports of regional centers, «maps of the surveillance of a case of suspected measles…», information and analytical bulletins of the National scientific and methodological center for the supervision of measles and rubella (NNMC). A total of 18,750 documents were analyzed. The average values, the average standard error, the correlation coefficient of the series, the reliability of the correlation coefficient, and the regression coefficient were calculated. Results and discussion. One of the indirect indicators of the state of population immunity is the ratio of vaccinated and not vaccinated against measles in the structure of patients. The analysis showed a steady trend towards the prevalence of cases not vaccinated against measles in the structure: since 2011, more than 70%, and since 2017 – more than 80%. The percentage of vaccinated people is decreasing from 12.8% to 5.4% (2017) and has stabilized in the last 2.5 years at the level of 5.4–7.2%. Over the past 2 years, there has also been some stabilization of the proportion of people twice vaccinated – 9.4–9.8%. Intensive indicators of morbidity confirmed the General trend of extensive indicators. In addition, over the past 3 years, the intensive incidence rate of those vaccinated is 14 times lower than that of those not vaccinated against measles. All this testifies to the lack of accumulation of susceptible individuals due to the loss of post-vaccination immunity and confirms the adequacy of the strategy and tactics of vaccination against measles in our country. The calculation of the regression coefficient showed that with an increase in vaccination coverage of the entire population by one percent, the incidence of measles among unvaccinated people will increase by 1.34 per one hundred thousand unvaccinated people against measles. The prevalence of foci without infection spread (more than 80%) during the analyzed period, and the restriction of secondary measles spread by the second generation of infection reproduction in foci with two or more cases of measles, multiple circulation of genotypes and subtypes of the measles virus also characterizes a fairly high population immunity. Conclusion. The steady predominance of lesions 1 case, limiting secondary spread of infection in outbreaks, the maintenance of the epidemic process of measles through an unvaccinated population indicate adequate tactics and strategy for measles immunization in our country. At the same time, the achieved 74.1% vaccination coverage of the entire population is clearly not enough to prevent sustained endemic transmission of the measles virus, since the reproductive index R<1 can be maintained with vaccination coverage of at least 95%. To increase population immunity, it is necessary to search for new forms of work of pediatricians and therapists with the population to form a commitment to immunization, as well as to legislate responsibility for the consequences of refusing vaccinations, as is done in a number of States. © Tsvirkun OV et al.