Comparison of measles incidence in different age groups with the intensity of specific humoral immunity in healthcare workers in Moscow

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The study of the intensity of humoral immunity to the measles virus (Paramyxoviridae: Morbillivirus) (MV) remains relevant due to the ongoing registration of the cluster cases of measles (including nosocomial cases).The aim of the study was to analyze correlation between the intensity of the humoral immunity to measles virus and the measles incidence in different age groups of the Moscow residents. A simple analytic study was carried out under the framework of measles prevention improvement program conducted in the subjects of the Russian Federation. The study included the analysis of the reasons for the increase in the proportion of seronegative individuals and the comparison of the results of seromonitoring with the data of age-related measles incidence. Throughout 2018, total 1,855 blood serum samples obtained from employees of a large hospital center in Moscow who were previously vaccinated against measles were tested for IgG antibodies (ABs) to MV. The subjects were divided into 11 groups according to their age. Statistical analysis of the obtained data was performed using nonparametric criteria. The proportion of seronegative individuals among the staff of the medical facility decreased with age, from 38.5% in persons aged 19-23 to 0% among employees aged 64 and over. Persons aged 19-43 years were the most susceptible to measles infection, which was confirmed also by the highest incidence rate at these age groups (from 6.93 to 14.03 per 100,000 population). The age group most protected against measles was those over 64 years of age, who were all seropositive and had the lowest rates of incidence. This is probably due to the fact that by this age most of them have had a measles infection and have formed a sufficient immune response. At the same time, younger individuals living in the post-elimination era have only vaccine-induced ABs to MV, the level of which declines rapidly to non-protective values in the absence of boosterization due to the exposure to the wild-type strain of the pathogen. The monitoring of the MV-specific IgG- AB levels is required for employees in the medical institutions under the age of 35. Administration of the single dose of the appropriate vaccine is recommended for seronegative individuals.