PROS1 and COVID-19: In this investigation, we evaluated the safety, immunogenicity, and efficacy in rhesus macaques of a COVID-19 vaccine candidate based on the poxvirus MVA vector expressing a human codon-optimized full-length SARS-CoV-2 S protein (MVA-S), which was previously reported to induce potent B- and T-cell immune responses and full efficacy in mice (16, 17, 19).