Clinical Trial to Assess Safety and Immunogenicity of Gam-COVID-Vac Combined Vector Vaccine for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-Сov-2) Infection

Inclusion Criteria: 1. Written informed consent of a subject to participate in the trial 2. Males and females aged 18+ years 3. Negative human immunodeficiency virus (HIV 1 \& 2) and hepatitis B and C test results 4. Negative immunoglobulin M (IgM) and immunoglobulin G (IgG) SARS-CoV-2 antibodies through enzyme immunoassay test result 5. Negative COVID-2019 Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) test result at the screening visit (72 hours prior to Visit 1 \[Day 1\]) 6. No COVID-2019 in the medical history 7. History of no contact with COVID-2019 persons within at least 14 days before the enrolment (according to subjects) 8. Consent for using effective methods of contraception during the entire trial 1 9. Negative urine pregnancy test at the screening visit (for child-bearing age women) 10. No evident vaccine-induced reactions or complications after receiving immunobiological products in the medical history 11. No acute infectious and/or respiratory diseases within at least 14 days before the enrolment. Exclusion Criteria: 1. Any vaccination/immunization within 30 days before the enrolment 2. Steroids (except hormonal contraceptives) and immunoglobulins or other blood products therapy not finished 30 days before the enrolment 3. Immunosuppressors therapy finished within 3 months before the enrolment 4. Pregnancy or breast-feeding 5. Acute coronary syndrome or stroke suffered less than one year before the enrolment 6. Tuberculosis, chronic systemic infections 7. Drug allergy (anaphylactic shock, Quincke edema, polymorphic exudative eczema, atopy, serum disease),hypersensitivity or allergic reaction to immunobiological products, known allergic reactions to study product components, acute exacerbation of allergic diseases on the enrolment day 8. Subjects who are on drugs that could have potential drug interactions with adenovirus vaccine 9. Medical history of malignancy 10. Donated blood or plasma (450+ mL) within 2 months before the enrolment 11. Splenectomy in the medical history 12. Neutropenia (absolute neutrophil count less than 1,000 mm3), agranulocytosis, significant blood loss,severe anaemia (haemoglobin less than 80 g/L), immunodeficiency including autoimmune disorders in the medical history within 6 months before the enrolment 13. Active form of a disease caused by the HIV and hepatitis B or C 14. Anorexia, protein deficiency of any origin 15. Tattoos at the injection site (deltoid muscle area), which does not allow assessing the local response to the IMP or placebo administration 16. Alcohol or drug addiction in the medical history. 17. Participation in any other interventional clinical trial within 1 month prior to the Screening 18. Any other medical condition that would limit the participation of the subject as per Investigator discretion 19. Study centre staff or other employees directly involved in the trial and their families 20. Subjects contraindicated for vaccination