Open-label, Non-randomized, Non-comparative, Phase II Study of Safety and Immunogenicity of Combination of AZD1222 and rAd26-S for COVID-19 Prevention

The purpose of the study is to assess safety and immunogenicity of heterologous booster vaccine containing combination of AZD1222 and rAd26-S (one of components of Gam-COVID-Vac vaccine) in adult subjects aged ≥ 18 years old to prevent COVID-19 spread.

This clinical study is a prospective, single-center, open-label, non-comparative, non-randomized single-arm study. It will enroll adult subjects aged ≥ 18 years old with absence of active COVID-19 infection to be verified by the results of reverse transcription polymerase chain reaction (RT-PCR). 100 subjects meeting inclusion criteria are expected to be screened, 100 of them meeting eligibility criteria will receive one intramuscular injection of AZD1222 vaccine at 5×10\^10 viral particles (nominal dose) and at least 90 subjects per one intramuscular injection of rAd26-S at (10±0.5) 1\*10\^11 viral particles with a 4-week interval on study days 1 and 29, respectively. Duration of the subject participation in the study will be 6 months (180±10 days) from the day of administration of the first dose of AZD1222 vaccine. 10 visits are scheduled for each subject, 8 of them being obligatory personal visits to the study site. Safety will be assessed for the duration of the study as follows: * Solicited adverse events (AEs) (local and systemic) will be assessed for 7 days following each vaccination (ie, on days 1-7 after the first vaccination and on study days 29-35 to account for AEs after second vaccination) at the study visits and based on the results of Subject Diary review. * Unsolicited AEs will be recorded within 29 days after administration of each dose of AZD1222/rAd26-S vaccine (i.e. on days 1-29 and on days 29 to 57). * Serious adverse events (SAEs) will be recorded from signing of the informed consent form through Day 180 * Adverse events of special interest (AESI) will be documented from the first vaccination until day 180. Immunogenicity will also be assessed throughout the study and include serological assay of levels of antibodies specific for Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen as well as level of seroconversion, tests for neutralising antibodies. At least 100 subjects are expected to receive at least one dose of the study product in 1 study site on the territory of Republic Azerbaijan.