In phase 1 of the study, one dose of either rAd26 OR rAd5 was given and were assessed over 28 days for the safety of each component individually, with clinical and laboratory assessments on days 0, 2, and 14. Participants' immune status was analyzed on days 0 and 28. After concluding the safety of the individual components, phase 2 began and participants received the prime-boost vaccination (rAd26-S) on day 0 and the rAd5-S on day 21, undergoing assessments on days 0, 14, 28, and 42. On days 0, 28, and 42, they assessed the immune status of the participants. Volunteers were in hospital for the first 28 days from the start of vaccination and information on adverse events was recorded daily for both phases. To compare post-vaccination immunity with the natural immunity that forms during infection with SARS-CoV-2, they obtained convalescent plasma from blood samples of 4817 people from Moscow who had recovered after COVID-19.