GRAd-COV2

Multicenter Study assessing the safety, efficacy, and immunogenicity of the candidate vaccine GRAd-COV2, compared to placebo, for the prevention of COVID-19. Participants will be adults ≥ 18 years of age who are healthy or have medically stable chronic diseases and are at increased risk for SARS-CoV-2 acquisition and COVID-19. In the phase II part approximately 900 participants will be randomized in a 1:1:1 ratio to receive i) 2 repeated (21 days apart) intramuscular (IM) doses of GRAd-COV2 at 1x10^11 viral particle (vp) (n = approximately 300 subjects) ii) 1 single IM dose of GRAd-COV2 at 2x10^11 vp plus 1 dose of placebo after 21 days (n= approximately 300 subject) or 2 doses of placebo (n = approximately 300 subjects) on day 1 and day 22. There will be 3 strata for randomization: ≥ 65 years, < 65 years and categorized to be at increased risk ("at risk") for the complications of COVID-19, and < 65 years "not at risk". Risk will be defined referring to the study participants' relevant past and current medical history. An independent Data Safety Monitoring Board will provide oversight, to ensure safe and ethical conduct of the Study; a Steering Committee will revise safety data (collected for 900 participants 1 week after dosing) and immunogenicity data (collected for 450 participants 5 weeks after the first dosing) generated in phase II part. Jointly DSMB and SC will recommend the expansion to phase III and the best regimen to be used.