HERD IMMUNITY TO DIPHTHERIA IN THE POPULATION OF SEVERAL RUSSIAN REGIONS

Introduction. Diphtheria is a serious infection, often characterized by a pronounced toxic component, which can be accompanied by severe complications of the cardiovascular and nervous systems. The primary method of infection prevention is immunization (primarily in children) with diphtheria toxoid, which induces effective and long-lasting antitoxic immunity. Objective of the study: evaluation of collective immunity to the causative agent of diphtheria among the population of several regions (Amur, Irkutsk, Nizhny Novgorod, Kaliningrad) and the Republic of Crimea. Materials and methods. The cross-sectional cohort randomized study involved 18,207 people uniformly stratified by age (1–5, 6–11, 12–17, 18–29, 30–39, 40–49, 50–59, 60–69, 70+ years), including: 3,576 in Amur; 3,657 in Irkutsk; 3,580 in Nizhny Novgorod; 3,613 in Kaliningrad regions; and 3,781 in the Republic of Crimea. All studies were conducted in strict accordance with the requirements of the Declaration of Helsinki. Immunoglobulin G Abs to the C. diphtheriae toxin were determined in the examined volunteers by enzyme immunoassay using a Russian-made test system. Data analysis and statistical processing were carried out using a web application. Results. The average cohort regional seroprevalence levels were: Amur Region - 82.3% (95% CI: 81.0 - 83.5); Irkutsk - 87.6% (95% CI: 87.6-88.9); Nizhny Novgorod - 86.5% (85.3-87.6); Kaliningrad - 74.2% (95% CI: 72.8 - 75.6); and the Republic of Crimea - 74.8% (95% CI: 73.4-76.1). In some cases, seropositivity did not reach 60%, namely: among individuals aged ≥60 in the Kaliningrad Region and the Republic of Crimea; and among individuals aged ≥70 in the Amur and Nizhny Novgorod Regions. Most volunteers had serum IgG Abs to diphtheria toxin at concentrations of 0.1–1.0 IU/ml, regardless of age, region, or vaccine type. Conclusion. The level of collective immunity mandated by current Russian documents (95% in children, 90% in adults) was practically not achieved in any region or age group (except children aged 1–5 years in the Irkutsk and Nizhny Novgorod Regions). In all regions, the least protected group were individuals aged 60 and older, among whom the seronegative value reached 30–45%.

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