Phase 3: Percentage of Participants; (SARS-CoV-2 seronegative at baseline); With Virologically-confirmed COVID-19 Disease;Phase 2: Change From Baseline in Neutralizing Antibody Response Measured by a Pseudovirus-based Neutralization Assay;Phase 2: Change From Baseline in Antigen-specific Cellular Immune Response Measured by Interferon-gamma (IFN-?) Enzyme-linked Immunospot (ELISpot) Assay

Phase 3: Percentage of Participants; (SARS-CoV-2 seronegative at baseline); With Virologically-confirmed COVID-19 Disease;Phase 2: Change From Baseline in Neutralizing Antibody Response Measured by a Pseudovirus-based Neutralization Assay;Phase 2: Change From Baseline in Antigen-specific Cellular Immune Response Measured by Interferon-gamma (IFN-?) Enzyme-linked Immunospot (ELISpot) Assay