Dynamics of changes in the number of SARS-CoV-2 seropositive patients over two years of the COVID-19 pandemic

Serological assays, being rapid and relatively inexpensive methods for detecting COVID-19, may play an important role in combating the SARS-CoV-2 pandemic. The aim of the present study was to assess dynamics of changes in the number of seropositive patients for SARS-CoV-2 antibodies over 2.5 years of the evolving COVID-19 pandemic. The study included 6051 persons (2840 women and 3211 males). Their mean age was 41.680.17 years (MSEM). At the time of this survey, all participants were residents of the Chelyabinsk region. General information was collected over the period from 06/01/2020 to 01/18/2022. Seropositivity for SARS-C0V-2 was assessed by test kits for IgG, IgM and IgA antibodies (JSC Vector-Best, Novosibirsk, Russia) against SARS-CoV-2 using indirect two-stage enzyme immunoassay (ELISA). Over the entire period, 27 cases were seronegative (20.45%); 99 samples were positive for IgA to SARS-CoV-2 (75%), and 6 samples (4.55%) yielded questionable ELISA results. IgG testing for SARS-Cov-2 antibodies was negative in 2433 cases (42.35%); 3245 samples (56.48%) were positive, and 67 specimens provided (1.17%) doubtful results using ELISA tests. IgM antibodies were not revealed in 2710 (70.41%) cases; 996 were positive (25.88%), and 143 specimens (3.72%) yielded doubtful results by ELISA technique. In general, the highest proportion of positive results was found in class A immunoglobulins. The wave-like distribution of the density among all antibody-positive patients was revealed, which, however, was not associated with peak values of COVID-19 morbidity in Chelyabinsk Region. Most waves of seroprevalence were detected before the waves of SARS-CoV-2 infection. A positive relationship was established between IgG and IgM seropositivity against SARS-CoV-2 with age and female gender. Conclusion. In general, serological testing and regular monitoring of antibodies against SARS-CoV-2 may play an important role in assessing its prevalence during the coronavirus pandemic and immune response to the infection at a population level.