Herd Immunity to SARS-CoV-2 among the Population in Saint-Petersburg during the COVID-19 Epidemic

• Main Authors: A. Yu. Popova, E. B. Ezhlova, A. A. Mel’nikova, N. S. Bashketova, R. K. Fridman, L. V. Lyalina, V. S. Smirnov, I. G. Chkhindzheriya, T. A. Grechaninova, K. A. Agapov, N. A. Arsent’eva, N. A. Bazhenova, O. K. Batsunov, E. M. Danilova, E. V. Zueva, D. V. Komkova, R. N. Kuznetsova, N. E. Lyubimova, A. N. Markova, I. V. Khamitova, V. I. Lomonosova, V. V. Vetrov, A. M. Milichkina, V. G. Dedkov, A. A. Totolyan
• Format: Article
• Language: Russian
• Published: Federal Government Health Institution, Russian Research Anti-Plague Institute “Microbe” 2020-10-01
• Series: Проблемы особо опасных инфекций
• Subjects: coronavirus sars-cov-2; covid-19; seroprevalence; incidence; asymptomatic infection
• Online Access: https://journal.microbe.ru/jour/article/view/1372

The first case of COVID-19 was diagnosed in St. Petersburg on March 2, 2020; the period of increase in the incidence lasted for 10 weeks, the maximum rates were recorded in mid-May, and subsequently there was a statistically significant decrease in the incidence.Objective: to determine the level and structure of community immunity to SARS-CoV-2 among the population of St. Petersburg during the period of intensive spread of COVID-19.Materials and methods. Selection of volunteers for the study was carried out through interviewing and randomization. The exclusion criterion was active COVID-19 infection at the time of the survey. 2713 people aged 1 to 70 years and above were  examined for the presence of specific antibodies to SARS-CoV-2. Antibodies were detected by enzyme immunoassay.Results and discussion. Studies have shown that in St. Petersburg, in the active phase of COVID-19 epidemic, there was a moderate seroprevalence to SARS-CoV-2, which amounted to 26 %, against the background of a high frequency (84.5 %) of asymptomatic infection in seropositive individuals who did not have a history of COVID-19 disease, positive PCR result and ARI symptoms on the day of examination. The maximum indicators of herd immunity were established in children 1–6 years old (31.1 %), 7–13 years old (37.7 %) and people over 70 years old (30.4 %). Differences in the level of seroprevalence in the age groups of 18–49 years are statistically significant. The highest level of seroprevalence was found among the unemployed (29.7 %), healthcare workers (27.1 %), education sector (26.4 %) and business sector personnel (25 %). In convalescents, COVID-19 antibodies are produced in 75 % of cases. In individuals with positive result of PCR analysis carried out earlier, antibodies are detected in 70 % of the cases. The results of the study of herd immunity to SARS-CoV-2 are essential to forecast the development of the epidemiological situation, as well as to plan measures for specific and non-specific prevention of COVID-19.