Studying Humoral Immune Response at Mild and Asymptomatic COVID-19 Forms

Background. Currently, during the COVID-19 pandemic, one of the most pressing healthcare problems is to ensure the safety of the population of the Russian Federation. There is insufficient information on the duration and intensity of post-infectious immunity in relation to SARS-CoV-2, especially in case of inapparent (without clinical signs), mild or latent forms of infection.

Materials and methods. The study involved 99 volunteers with a laboratory confirmed PCR diagnosis of COVID-19 who were residents of the Irkutsk Region and of other regions of the Russian Federation and arrived to work in Bodaybo on a rotational basis. Also the study included 50 conditionally healthy people living in Irkutsk who had negative PCR results for SARS-CoV-2 RNA presence.
Specific IgG and IgM antibodies to SARS-CoV-2 were detected in blood serum by enzyme-linked immunosorbent assay (ELISA) using test systems “ELISA anti-SARS-CoV-2 IgG” (FBUN SSC PMB, Obolensk, Russian Federation), “SARS-CoV-2-IgG-IFA-BEST” and “SARS-CoV-2-IgM-IFA-BEST” (Vector-Best, Novosibirsk, Russian Federation).

Results. The results of a study of the humoral immunity of patients with asymptomatic and clinical forms of COVID-19 are presented. The data indicate the production of specific IgG in the blood serum of people in 2–3 weeks after SARSCov-2 infection and reaching its maximum level on the 20–21st day. The seroconversion rate  was 94.9 %. It was shown that the geometric mean titer of antibodies in asymptomatic and mild forms of coronavirus infection did not differ statistically and amounted to 1:512 and 1:632, respectively. Higher titers of antibodies (1:1600) were detected in the moderate form.

Conclusion. The research results can serve as a basis for studying the dynamics of changes in the indicators  of the humoral immune response in patients with COVID-19 and for clarifying the duration of their post- infectious immunity in order to predict the development of the epidemic situation and to ensure the planning of specific prevention.

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