Safety and Immunogenicity Study in Adults of AZD1222 and rAd26-S Administered as Heterologous Prime Boost Regimen for the Prevention of Coronavirus Disease 2019 (COVID-19)

This is a Phase I/II, parallel group, single blinded (participant blinded), randomised study assessing the immunogenicity and safety of AZD1222 and rAd26-S administered as heterologous prime-boost in alternating order in 2 study groups for the Prevention of COVID-19.

This is a prospective, single blinded randomised clinical study, designed to provide data on the heterologous prime boost use of AZD1222 and rAd26-S, to be administered one after the other interchangeably. This study aims to explore the immunogenicity and safety of combining these 2 different adenovirus vector vaccines in the prevention of coronavirus disease 2019 (COVID-19).

Participants will be healthy adults ≥ 18 years of age.

Approximately 100 participants will be randomised (1:1) to one of the following groups:

- Group A: 1 intramuscular (IM) injection of 5×10^10 vp (nominal) of AZD1222 on Day 1 followed by rAd26-S (1.0±0.5) х 10^11vp (nominal) on Day 29.
- Group B: 1 IM injection of rAd26-S (1.0±0.5) х 10^11vp (nominal) on Day 1 followed by AZD1222 5×10^10 vp (nominal) on Day 29.

Immunogenicity will be assessed for the duration of the study, including serologic quantification of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) antigen specific antibody levels and antibody seroconversion rate, neutralising antibody assays and cellular immunity testing.

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 (Day 1 through Day 7 for first vaccination and Day 29 through Day 35 for second vaccination).
- Unsolicited AEs will be recorded for 29 days following each vaccination (ie, until Day 29 following the first vaccination and Day 57 following the second vaccination).
- Serious adverse events (SAEs) will be recorded from signing of the informed consent form through Day 180. However, the safety endpoint for SAEs will be assessed after the first vaccination (see Section 12.2).
- Adverse events of special interest (AESIs) will be recorded from first vaccination through Day 180.

This study is going to be conducted in the United Arab Emirates. All participants will remain on study for 6 months (180 days) following the first vaccination.