Key Inclusion Criteria:  Meets ≥1 of the following criteria:  Is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, HIV, rheumatological disease, autoimmune disease, multiple sclerosis OR Currently taking immunosuppressant drugs Have been fully vaccinated against COVID-19 or deemed medically ineligible to receive full course of vaccine Has documented negative serology/antibody response in an anti-SARS-CoV-2 spike protein IgG clinical test collected ≤72 hours prior to randomization Tested negative for the COVID-19 virus  Key Exclusion Criteria:  Weighs <40 kg (only applies to participants ≥12 to <18 years of age) Has any signs or symptoms consistent with COVID-19 Past COVID-19 infection within 90 days prior to randomization Planned use of any investigational, authorized, or approved vaccine for COVID-19 within 90 days of the last dose of study drug Prior (within 30 days), current, or planned use of any of COVID-19 convalescent plasma, other monoclonal antibodies against SARS-CoV-2 or any COVID-19 treatment Is planned to begin immunoglobulin (IVIG) or immunoglobulin (SCIG) therapy, is planned to have a change to existing IVIG or SCIG, or has been on a chronic stable dose of their IVIG or SCIG regimen for less than 90 days prior to screening Has any known active acute respiratory infection Has persistent (refractory to treatment for ≥14 days) bacterial or fungal infection Has known allergy or hypersensitivity to components of the study drugs  NOTE: Other Protocol Defined Inclusion/Exclusion Criteria Apply