COVID-19 Study to Evaluate Safety, Tolerability, and Efficacy of REGN14256+Imdevimab for the Treatment of COVID-19 Adult and Adolescent Patients Without Risk Factors for Progression to Severe Disease

Phase 1 will enroll adult patients (≥18 years of age), Phase 2 will enroll adult patients, Phase 3 will enroll adult patients and an additional adolescent cohort of patients (≥12 and \<18 years of age) Key Inclusion Criteria: 1. For the adolescent cohort in Phase 3 only: Weighs ≥40 kg at randomization 2. Has SARS-CoV-2-positive antigen or molecular diagnostic test (by validated SARSCoV-2 antigen, RT-PCR, or other molecular diagnostic assay, using an appropriate sample such as nasopharyngeal \[NP\], nasal, oropharyngeal \[OP\], or saliva) ≤72 hours prior to randomization. A historical record of a positive result is acceptable as long as the sample was collected ≤72 hours prior to randomization 3. Has symptoms consistent with COVID-19 (as determined by the investigator) with onset ≤7 days before randomization, and doesn't have a medical condition or other factors associated with high risk for progression to severe COVID-19 as outlined in the exclusion criteria 4. Maintains O2 saturation ≥93% on room air Key Exclusion Criteria: 1. Has a medical condition or other factors associated with high risk for progression to severe COVID-19: 1. Cancer 2. Cardiovascular disease (such as heart failure, coronary artery disease, cardiomyopathies, congenital heart disease or hypertension) 3. Chronic lung disease including chronic obstructive pulmonary disease, asthma (moderate to severe), interstitial lung disease, cystic fibrosis, and pulmonary hypertension 4. Chronic kidney disease at any stage 5. Chronic liver disease (such as alcohol-related, nonalcoholic fatty liver disease, cirrhosis) 6. Dementia or other chronic neurological condition 7. Diabetes mellitus (type 1 or type 2) 8. Immunodeficiency disease or taking immunosuppressive treatment 9. Medical-related technological dependence \[for example, tracheostomy, gastrostomy, or positive pressure ventilation (not related to COVID-19)\] 10. Neurodevelopmental disorder (for example, cerebral palsy) or other condition that confers medical complexity (for example, genetic or metabolic syndromes and severe congenital anomalies) 11. Overweight (defined as BMI \>25 kg/m2) or obesity (defined as BMI ≥30 kg/m2) 12. Poorly controlled HIV infection or AIDS 13. Pregnancy 14. Sickle cell disease or thalassemia 15. Stroke or cerebrovascular disease 2. Prior, current (at randomization) or planned use (within time period given per CDC guidance \[90 days\]) of any authorized or approved vaccine for COVID-19 3. Was admitted to a hospital for COVID-19 prior to randomization, or is hospitalized (inpatient) for any reason at randomization 4. Has a known prior SARS-CoV-2 infection or positive SARS-CoV-2 serologic test 5. Has a positive SARS-CoV-2 antigen or molecular diagnostic test from a sample collected \>72 hours prior to randomization 6. Has participated, or is participating, in a clinical research study evaluating COVID-19 convalescent plasma, mAbs against SARS-CoV-2, or intravenous immunoglobulin (IVIG) within 3 months or within 5 half-lives of the investigational product (whichever is longer) prior to the screening visit 7. Prior, current, or any of the following treatments: COVID-19 convalescent plasma, mAbs against SARS-CoV-2, IVIG (any indication), systemic corticosteroids (any indication), or COVID-19 treatments (authorized, approved, or investigational) 8. Has known active infection with influenza or other non-SARS-CoV-2 respiratory pathogen, confirmed by a diagnostic test 9. Has been discharged, or is planned to be discharged, to a quarantine center 10. Has participated, is participating, or plans to participate in a clinical research study evaluating any authorized, approved, or investigational vaccine for COVID-19 11. For Phase 1only: Women of childbearing potential (WOCBP) who are unwilling to practice highly effective contraception prior to the initial dose/start of the first treatment and for at least 6 months after study drug administration as described in the protocol Note: Other protocol-defined inclusion/ exclusion criteria apply