Assessment of the State of Antidiphtheria Immunity in Different Age Groups of the Population of the Russian Federation Based on Seromonitoring Data for 2015–2021

Relevance . Diphtheria is one of the dangerous diseases that threaten human life. Immunization is the only means of creating a favorable epidemiological situation. Ensuring the immunity of the population to this infection prevents the occurrence of the rise and spread of diphtheria among the population. One of the ways to assess the state of specific immunity to diphtheria is annual serological monitoring. Aims . Assessment of the state of antidiphtheria immunity in different age groups of the population of the Russian Federation based on seromonitoring data for 2015–2021. Materials and methods . The data of serological monitoring of diphtheria and the state of vaccination of the population by indicator groups from 85 subjects of the Russian Federation in 2015–2021 were analyzed. In just 7 years, in terms of seromonitoring in Russia, 439,874 people were examined for the presence of antibodies to diphtheria, including 73,559 children in the age group of 3–4 years, 74,424 adolescents aged 15–17 years, and 291,891 adults aged 18 and older. During the same period, 12,154 controlled blood sera from 20 subjects of the Russian Federation were examined. In the age group of 3–4 years – 1834 children, 15–17 years – 1366 teenagers, 18–29 years – 1711 adults, 30–39 years – 1724 adults, 40–49 years – 1918 adults, 50–59 years – 1798 adults, 60 years and older – 1803 adults. The presence of antibodies to diphtheria was determined in the course of passive hemagglutination. The protective titers of antibodies were taken to be dilution of sera with a titer of 1:20 or more, the intensity of anti-diphtheria immunity was assessed as follows: antibody titers in dilution of sera 1:20–1:40 – low titers, 1:80–1:160 – medium and 1:320 or more – high titers of antibodies of JSC «Biomed» im. I. I. Mechnikov. Results and discussion . In Russia, improving the surveillance system for diphtheria continues to be an urgent task of the private epidemiology of this infection. The data obtained during the study allowed us to characterize the population immunity of the population of the Russian Federation, as a whole across the country, as sufficient to prevent the occurrence and spread of diphtheria. The main factor contributing to this was the long-term high coverage of vaccinations against diphtheria of persons in the decreed age groups (more than 95% of those vaccinated from the number of persons to be vaccinated in each age group). When comparing the level of immunization of the population depending on age, it was found that the percentage of vaccinated persons in the age group of people 50 years and older was statistically significantly lower than in the group of people younger than 50 years. The data of serological studies in Russia as a whole showed a high proportion of people with protective titers of antibodies to diphtheria in each age group – 3–4 years – 96.7 ± 0.1%, 15–17 years – 98.3 ± 0.1%, 18–29 years – 96,0 ± 0,4% – 97,5 ± 0,3%, 30–39 – 95,9 ± 0,4% – 97,5 ± 0.3%, 40–49 years old – 95,7 ± 0,4% – 97,7 ± 0,3%. The largest proportion of seronegative individuals is detected among groups aged 50–59 years and 60 years and older. The analysis of the share of seronegative persons in certain subjects of the Russian Federation revealed that the number of territories with a share of seronegative persons of more than 10% in the age groups of 50–59 years and 60 years and older was significantly higher than in other age groups. Conclusion . Thus, when planning companies for «сatch-up» immunization, it is advisable to provide mandatory revaccination of seronegative persons over 50 years of age. Timely revaccination according to the National Vaccination Calendar, tracking the proportion of persons susceptible to diphtheria in all indicator groups, followed by revaccination of seronegative persons in older ages will allow maintaining a high level of population immunity (more than 95%) and ensuring a consistently low incidence of diphtheria in the country for many years.