An Open Study of the Safety, Tolerability and Immunogenicity of the Drug "Gam-COVID-Vac" Vaccine Against COVID-19

The purpose of the study is to assess safety, tolerability and immunogenicity of the drug "Gam-COVID-Vac ", a solution for intramuscular administration, with the participation of healthy volunteers Study objectives A safety and tolerability assessment of the drug "Gam-COVID-Vac ", solution for intramuscular administration, using single dose of each component (Stage 1). A safety and tolerability assessment of the drug "Gam-COVID-Vac ", solution for intramuscular administration, using prime-boost immunization according to the proposed scheme (Stage 2). Post-vaccination immunity assessment at different time points after vaccination by: * Determination of antigen-specific antibody titer in blood serum by ELISA by comparison with baseline values before the vaccine administration and at days 14, 21, 28, and 42 after vaccination (hereinafter, the countdown comes from the first time of the vaccine administration); * Determination of virus neutralizing antibody titer before and at days 14, 28, and 42 after vaccination; * Determination of antigen-specific cellular immunity (specific T-cell immunity) before the vaccine administration and at days 14 and 28 after vaccination.