To evaluate the dynamics of IgG levels to the SARS-CoV-2 virus after a booster dose of Soberana Plus vaccine.

Prospective clinical study of evaluation of the immune response to booster dose of vaccine against COVID-19 using enzyme immunoassay using the Sunrise Tecan microplate photometer (Austria). The material is participants' plasma, obtained by the standard method. Blood sampling performed 4 times: immediately before the first dose of vaccine, on day 42, 90 days and 180 days after booster dose of vaccine. Booster dose of vaccine against coronavirus infection performing using approved and licensed vaccine Soberana Plus (Republic of Cuba). Venous blood sampling performing standardly. All study participants are informed about the study objectives and upcoming procedures, and all of them given informed written consent to participate the study.

A reagent kit manufactured by Vector-Best (Russian Federation) and designed for enzyme immunoassay for quantitative detection of SARS-CoV-2 class G immunoglobulins, SARS-CoV-2-IgG quantitative ELISA-BEST, D-5505 SARS-CoV-2-IgG (series 5, 6) РУ № РЗН 2022/17065Т used for immunoassay. The "SARS-CoV-2-IgG quantitative ELISA-BEST" reagent kit design uses recombinant full-length trimerized S glycoprotein (Spike) of the SARS-CoV-2 virus derived from a eukaryotic expression system. The protein molecule+ consists of two subunits, S1 containing the RBD domain and S2. The reagent kit "SARS-CoV-2-IgG quantitative ELISA-BEST" detects the pool of immunoglobulin class G synthesized to all antigenic determinants of protein S including the RBD-domain.

The quantification of the SARS-CoV-2 antibody assay is based on the WHO First International Standard (NIBSC code:20/136) and expressed in international units (BAU/ml).

Analytical characteristics of reagent kit "SARS-CoV-2-IgG quantitative ELISA-BEST (series 5, 6)" were: Linearity - within 90-110%, considering the analytical results at wavelengths 405 nm and 415 nm - within the concentration range IgG к SARS-CoV-2 10-5000 BAU/ml; Reproducibility: the coefficient of variation does not exceed 8%). The "opening" test - within 90-110% (samples with absorbances lower than 90% of the cut-off value are considered negative and samples with absorbances higher than 110% of the cut-off value are considered positive. The samples with absorbance in the range of 90-110% of cut-off value are equivocal). Analytical sensitivity - minimal detectable concentration of IgG to SARS-CoV-2 does not exceed 1.0 BAU/ml.

Inclusion Criteria:

1. Age 18-80 y.o.;
2. More that 4 months after the previous vaccination against COVID-19;
3. No COVID-19 infection registered within 30 days prior to Soberana Plus administration.

Exclusion Criteria:

1. Age less than 18 y.o. or more than 80 y.o.;
2. Less than 4 months after the previous vaccination against COVID-19;
3. COVID-19 infection registered within 30 days prior to Soberana Plus administration.