In this study, Phase II part will evaluate the efficacy, safety and PK of SCTA01 low dose+BSC, high dose+BSC and placebo+BSC in patients with severe COVID-19.~In Phase II part, subjects will be randomized at 1:1:1 ratio. At the end of Phase II part, a dose for the Phase III will be determined.~The Phase III part will evaluate the efficacy, safety, and immunogenicity of SCTA01 at the recommended dose recommended. Subjects in Phase III part will be randomized at 1:1 ratio to SCTA01+BSC and placebo+BSC groups.
The study is a multicenter, adaptive, randomized, double-blinded and placebo-controlled Phase II/III trial, and will be conducted globally. The study is comprised of two parts: dose selection (Phase II) and pivotal treatment effect (Phase III).