Features of the population immunity to SARS-CoV-2 development in staff members of medical organizations during the spread of COVID-19

Abstract

Background. The ongoing COVID-19 pandemic generates the urgent need of monitoring the herd immunity among healthcare workers as a high-risk group for infection. Aim. Determining the level and structure of population immunity to SARS-CoV-2 in the medical workers during the second peak of COVID-19 from August to November 2020. Material and methods. The study involved 15,158 medical workers from 91 medical organizations of the Republic of Tatarstan. The age of the examined stuff members varied from 18 to 74 years, the average age was 45.480.1016 years, most of them were women (13 627, 89.870.258%). Testing for the presence of total antibodies (immunoglobulin classes G, A and M) to SARS- CoV-2 was performed once by the enhanced chemiluminescence method. Statistical processing was carried out by methods of variation statistics and correlation analysis according to the Pearson method using MS Excel and WinPepi. Results. Seroprevalence to SARS-CoV-2 in medical workers was 35.230.388%. An increase in seropositive individuals level from 27.440.265% in August to 57.910.499% in November and an increase in the average geometric mean titer of total antibodies (immunoglobulin classes A, M, G) from 84.43 in August to 101.09 in November 2020 were detected. The level of individuals with antibodies increased with age from 18 to 59 years and decreased in group of 6070 years. The largest proportion of seropositive to SARS-CoV-2 individuals was found among junior (42.011.384%) and middle grade (37.50.527%) medical staff of hospitals for patients with COVID-19, ambulance and emergency stations. Among the seropositive to the SARS-CoV-2 workers the proportion of asymptomatic forms of infection was 84.970.498%. According to the level of seroprevalence, municipal districts of the Republic of Tatarstan were divided into three groups: moderate 8.939.0; average 42.949.6, high level 53.164.4. Сonclusion. An increase in seroprevalence to SARS-CoV-2 was revealed among medical workers of the Republic of Tatarstan from August to November 2020 during the second peak of COVID-19.