A Phase III Clinical Trial of the Immunogenicity and Safety of the Gam-COVID-Vac Vaccine Against COVID-19 in the UAE

The subjects will be randomized into two groups in the ratio of 1:3; a reference group of 250 subjects receiving placebo and a study group of 750 subjects receiving the Gam-COVID-Vac combined vector vaccine against the SARS-СoV-2-induced coronavirus infection. The trial subjects will be randomized into five age strata: 18-30, 31-40, 41- 50, 51-60, and 60+ years. Each subject will participate in the trial for 180±14 days after the first dose of the study vaccine/placebo and will have in total six on-site visits to the study physician during the study period and several follow-ups Phone Call/ Teleconsultation during the study as follow: * One Screening visit, i.e., Screening Visit = Day -7 to Day -1 * Two vaccination visits, i.e., o Visit 1 / Day1 * Tele-consultation / Phone Call to start on Day 2 and a weekly basis until visit 2 o Visit 2/ Day 21±2 Days * Tele-consultation / Phone Call to occur on Day 22±2 Days then on a weekly basis until visit 3. * Four Observational Visits to be scheduled as follow: * Visit 3/ Day 28 ±2 days * Weekly Follow Up Tele-consultation / Phone calls until visit 4 * Visit 4/ Day 42 ±4 days * Weekly Follow Up Tele-consultation / Phone Call until visit 5 * Visit 5/ Day 90 ±7 days * Weekly Follow Up Tele-consultation / Phone Call until visit 6 * Visit 6/ Day 120 ±14 days * Weekly Follow Up Tele-consultation / Phone calls until visit 7 * End of Study Visit/ Visit 7/ Day 180 ± 14 days The study vaccine/placebo will be administered intramuscularly during vaccination visits 1 and 2 (day 1 and day 21±2). Subsequent observation visits 3, 4, 5, 6 and end of study visit / EOS /Visit 7 will be made on days 28±2, 42±4, 90±7, 120±14 and D180±14 respectively. During the observation visits, vitals will be assessed in all trial subjects, and changes in the subjects' condition and wellbeing compared to the previous visit will be recorded. Blood samples will be collected per the schedule of assessment from all subjects during the following visits to assess the following immunogenicity parameters.