This is a study to see if an intravenous (IV) infusion of medication: REGN10933+REGN10987 is an effective and safe treatment for COVID-19. REGN10933+REGN10987 is an investigational medication which means they have not been approved by the FDA to treat COVID-19 or any other disease. Adult patients who are not hospitalized with COVID-19 (i.e. outpatient or ambulatory) and have COVID-19 symptoms may be eligible for this study. Participants will be randomly assigned to receive a onetime infusion of the medication or placebo. Study participation will last about 4 weeks and may include home home-based visits.

Treatment of chronic hepatitis C virus (HCV) infection is now possible with all oral medications. While most patients achieve a sustained virologic response (SVR) after treatment, synonymous with cure, some patients relapse after treatment for reasons that are unclear. The goal of this research is to understand how a person's immune system changes during treatment of HCV infection with all oral therapy, and how these changes might impact the chances of relapse after treatment. To address these questions, blood and clinical information will be collected from study participants over the course of receiving standard of care treatment for HCV infection. This blood and clinical information will be used to conduct laboratory research focused on the immune system.