SARS-CoV-2 Seroprevalence Structure of the Russian Population during the COVID-19 Pandemic

Abstract

The SARS-CoV-2 pandemic, which came to Russia in March 2020, is accompanied by morbidity level changes and can be tracked using serological monitoring of a representative population sample from Federal Districts (FDs) and individual regions. In a longitudinal cohort study conducted in 26 model regions of Russia, distributed across all FDs, we investigated the distribution and cumulative proportions of individuals with antibodies (Abs) to the SARS-CoV-2 nucleocapsid antigen (Ag), in the period from June to December 2020, using a three-phase monitoring process. In addition, during the formation of the cohort of volunteers, the number of seropositive convalescents, persons who had contact with patients or COVID-19 convalescents, and the prevalence of asymptomatic forms of infection among seropositive volunteers were determined. According to a uniform methodology, 3 mL of blood was taken from the examined individuals, and plasma was separated, from which the presence of Abs to nucleocapsid Ag was determined on a Thermo Scientific Multiascan FC device using the “ELISA anti-SARS-CoV-2 IgG” reagent set (prod. Scientific Center for Applied Microbiology and Biotechnology), in accordance with the developer’s instructions. Volunteers (74,158) were surveyed and divided into seven age groups (1–17, 18–29, 30–39, 40–49, 59–59, 60–69, and 70+ years old), among whom 14,275 were identified as having antibodies to SARS-CoV-2. The average percent seropositive in Russia was 17.8% (IQR: 8.8–23.2). The largest proportion was found among children under 17 years old (21.6% (IQR: 13.1–31.7). In the remaining groups, seroprevalence ranged from 15.6% (IQR: 8–21.1) to 18.0% (IQR: 13.4–22.6). During monitoring, three (immune) response groups were found: (A) groups with a continuous increase in the proportion of seropositive; (B) those with a slow rate of increase in seroprevalence; and (C) those with a two-phase curve, wherein the initial increase was replaced by a decrease in the percentage of seropositive individuals. A significant correlation was revealed between the number of COVID-19 convalescents and contact persons, and between the number of contacts and healthy seropositive volunteers. Among the seropositive volunteers, more than 93.6% (IQR: 87.1–94.9) were asymptomatic. The results show that the COVID-19 pandemic is accompanied by an increase in seroprevalence, which may be important for the formation of herd immunity.

Longitudinal Randomized Cohort Study of SARS-CoV-2 Antibody Seroprevalence in the St. Petersburg Population

“…From a practical point of view, epidemiological analysis of the state of collective immunity using serological methods (for determining the prevalence of SARS-CoV-2 Abs) and other epidemiological analysis approaches are more appropriate [ 12 , 13 ]. This article continues our previous publications analyzing SARS-CoV-2 Ab seroprevalence, such as our cross-sectional study of herd immunity in the St. Petersburg population [ 14 ] conducted in the early period of COVID-19 incidence (13–20 June 2020), as well as longitudinal seromonitoring of the population in 26 regions of Russia [ 15 , 16 , 17 , 18 , 19 , 20 ]. Features of seroprevalence in Belarus and Kyrgyzstan (2020–21) were also analyzed [ 21 , 22 ].…”

“…Previously, features of coronavirus infection and seroprevalence development dynamics (anti-SARS-CoV-2 Abs) in the Russian population in 2020 were characterized [ 1 , 15 , 16 ]. As mentioned above, the epidemic proceeded in St. Petersburg in the form of two waves (May and December 2020), of which the second was significantly higher ( p > 0.0001).…”

“…As noted, a characteristic feature of coronavirus infection is a significant proportion of patients with an asymptomatic course in which there are no clinical manifestations of disease yet Abs specific for SARS-CoV-2 Nc are produced. According to various sources, the number of such seropositive individuals can vary from 40% to 100% [ 14 , 16 , 38 , 39 ]. In the course of the staged survey of the St. Petersburg volunteer cohort, an absolute predominance of asymptomatic forms of infection (among SARS-CoV-2 seropositive individuals) was revealed ( Figure 5 , Table S4 ).…”

Herd immunity to SARS-CoV-2 among the population of the Republic of Belarus amid the COVID-19 pandemic

“…This is manifested as a high proportion of convalescents, although it is worth noting that a noticeable morbidity did not lead to the activation of transmission or the appearance of a significant number of contact persons. The age structure of seroprevalence, in contrast to a number of Russian regions [10,11,13,41], was characterized by a statistically significant increase in the indicator among persons in older age groups (50-70+ years; p < 0.0001) (Table 3). When quantifying Abs SARS-CoV-2 Nc, it was shown that: the minimum Ab levels (100 to 750 U/ml) prevailed among volunteers in the age groups 1-17 and 18-29 years old; and the maximum levels (751 to 3000+ U/ml) were identified among persons aged 50 to 70+ years.…”

Seropositivity of SARS-CoV-2 in the Population of Kazakhstan: A Nationwide Laboratory-Based Surveillance

“…For example, a seroprevalence study that used sera collected between 28 September and 30 December 2020, in the Chelyabinsk region of the Russian Federation, showed that the crude prevalence of anti-SARS-CoV-2 Spike IgM was 3.2% [ 14 ]. Another seroprevalence study performed on the population of 26 regions of the Russian Federation identified that 17.8% of individuals had IgG antibodies to SARS-CoV-2 [ 15 ]. Another seroprevalence study performed on the population of 26 regions of the Russian Federation identified that 17.8% of individuals had IgG antibodies to SARS-CoV-2 [ 16 ].…”