In this preprint, Gao et al. describe the first evidence of vaccine efficacy against COVID-19 in non-human primates. A patient-derived SARS-CoV-2 isolate was expanded then inactivated with β-propiolactone. Rhesus macaques were immunized three times with inactivated virus plus alum, then challenged 1 week later with a virus from a different isolate. Although SARS-CoV-2 infection of rhesus macaques doesn’t fully recapitulate human pathophysiology, vaccinated macaques had no symptoms and a rapid decrease in viral loads. Vaccine safety was assessed in additional macaques that showed no immediate adverse effects. This inactivation technique is well known and adaptable for production in other facilities, which argues for scalability. Phase I and II clinical trials are underway.