1. Age: a. Ph 2: Is an adult aged 18 years and above b. Ph 3: Is an adult aged 18 years and above or is an adolescent aged 12-17 years (inclusive) and weighing ≥40 kg at the time of screening 2. Has had SARS-CoV-2 positive antigen, RT-PCR, or other locally approved molecular diagnostic assay obtained within 5 days prior to randomization 3. Has had initial onset of one or more of the following self-reported COVID-19-related signs or symptoms within 5 days prior to randomization: (temperature ≥38°C, subjective fever, chills, cough, sore throat, congestion, shortness of breath or difficulty breathing with exertion worse than usual, muscle or body aches, fatigue, headache, loss of taste or smell, nausea or vomiting, diarrhea) 4. Has one or more of the following COVID-19-related signs or symptoms on the day of randomization (temperature ≥38°C, subjective fever, chills, cough, sore throat, congestion, shortness of breath or difficulty breathing with exertion worse than usual, muscle or body aches, fatigue, headache, loss of taste or smell, nausea or vomiting, diarrhea) 5. Is at high risk of disease progression defined as: a. Age >55 years b. Age 18 to ≤55 years with one or more stable preexisting medical conditions as follows i. Obesity [BMI ≥ 30 kg/m2] ii. Diabetes (Type 1 or Type 2) iii. Chronic kidney disease iv. Chronic lung disease v. Cardiac disease vi. Sickle cell disease or thalassemia vii. Solid organ or blood stem cell transplant recipients viii. Other immunodeficiency due to underlying illness or immunosuppressant medication ix. Down Syndrome x. Stroke or cerebrovascular disease, which affects blood flow to the brain xi. Substance use disorder xii. Pregnant (Phase 3 only, after review Ph2 data by iDMC) c. Age 12 to 17 years (inclusive) with one or more preexisting medical conditions as follows i. BMI >85th percentile for age and gender based on CDC growth charts ii. Diabetes (Type 1 or 2) iii. Chronic kidney disease iv. Sickle cell disease or thalassemia v. Congenital or acquired heart disease vi. Neurodevelopmental disorders vii. A medically related technological dependence viii. Asthma, reactive airway or other chronic respiratory disease that requires daily medication for control ix. Solid organ or blood stem cell transplant recipients x. Other immunodeficiency due to underlying illness or immunosuppressant medication xi. Substance use disorder xii Pregnant (Ph 3 only: enrollment only after Ph2 data reviewed by iDMC) 6. Has been assigned female sex at birth and is of nonchildbearing potential. A female participant who is not of reproductive potential is eligible without requiring the use of contraception and pregnancy testing is not required. This includes female participants who have not undergone menarche or who are documented to be surgically sterile or postmenopausal. Follicle stimulating hormone is not required in postmenopausal females with amenorrhea for >2 years. 7. Has been assigned female sex at birth and is of childbearing potential and fulfills all the following criteria: a. Has a negative urine or serum pregnancy test at Screening b. Has practiced adequate contraception for or has abstained from all activities that could result in pregnancy for at least 28 days prior to the first dose (Day 1) c. Has agreed to continue adequate contraception for sexual activity that could lead to pregnancy through 6 months following study drug administration d. Is not currently breastfeeding Adequate contraception for participants assigned female sex at birth is defined as consistent and correct use of a highly effective locally approved contraceptive method in accordance with local regulations for contraceptive use in clinical trial participants. 8. Has been assigned male sex at birth with partner(s) of childbearing potential and agree to use contraception, per local regulations, through 6 months after dosing. If their partner is pregnant, males must agree to use a condom. No sperm donation is permitted through 6 months after dosing. 9. Is able to understand and comply with study requirements /procedures (if applicable, with assistance by caregiver, surrogate, or guardian/[LAR]) based on the assessment of the investigator. 10. Is able and willing to provide informed consent. An LAR may be used only in cases where inclusion criterion 9 is able to be fulfilled. In the case of adolescents, informed assent must also be obtained as required by local guidelines.

1. Age: a. Ph 2: Is an adult aged 18 years and above b. Ph 3: Is an adult aged 18 years and above or is an adolescent aged 12-17 years (inclusive) and weighing ≥40 kg at the time of screening 2. Has had SARS-CoV-2 positive antigen, RT-PCR, or other locally approved molecular diagnostic assay obtained within 5 days prior to randomization 3. Has had initial onset of one or more of the following self-reported COVID-19-related signs or symptoms within 5 days prior to randomization: (temperature ≥38°C, subjective fever, chills, cough, sore throat, congestion, shortness of breath or difficulty breathing with exertion worse than usual, muscle or body aches, fatigue, headache, loss of taste or smell, nausea or vomiting, diarrhea) 4. Has one or more of the following COVID-19-related signs or symptoms on the day of randomization (temperature ≥38°C, subjective fever, chills, cough, sore throat, congestion, shortness of breath or difficulty breathing with exertion worse than usual, muscle or body aches, fatigue, headache, loss of taste or smell, nausea or vomiting, diarrhea) 5. Is at high risk of disease progression defined as: a. Age >55 years b. Age 18 to ≤55 years with one or more stable preexisting medical conditions as follows i. Obesity [BMI ≥ 30 kg/m2] ii. Diabetes (Type 1 or Type 2) iii. Chronic kidney disease iv. Chronic lung disease v. Cardiac disease vi. Sickle cell disease or thalassemia vii. Solid organ or blood stem cell transplant recipients viii. Other immunodeficiency due to underlying illness or immunosuppressant medication ix. Down Syndrome x. Stroke or cerebrovascular disease, which affects blood flow to the brain xi. Substance use disorder xii. Pregnant (Phase 3 only, after review Ph2 data by iDMC) c. Age 12 to 17 years (inclusive) with one or more preexisting medical conditions as follows i. BMI >85th percentile for age and gender based on CDC growth charts ii. Diabetes (Type 1 or 2) iii. Chronic kidney disease iv. Sickle cell disease or thalassemia v. Congenital or acquired heart disease vi. Neurodevelopmental disorders vii. A medically related technological dependence viii. Asthma, reactive airway or other chronic respiratory disease that requires daily medication for control ix. Solid organ or blood stem cell transplant recipients x. Other immunodeficiency due to underlying illness or immunosuppressant medication xi. Substance use disorder xii Pregnant (Ph 3 only: enrollment only after Ph2 data reviewed by iDMC) 6. Has been assigned female sex at birth and is of nonchildbearing potential. A female participant who is not of reproductive potential is eligible without requiring the use of contraception and pregnancy testing is not required. This includes female participants who have not undergone menarche or who are documented to be surgically sterile or postmenopausal. Follicle stimulating hormone is not required in postmenopausal females with amenorrhea for >2 years. 7. Has been assigned female sex at birth and is of childbearing potential and fulfills all the following criteria: a. Has a negative urine or serum pregnancy test at Screening b. Has practiced adequate contraception for or has abstained from all activities that could result in pregnancy for at least 28 days prior to the first dose (Day 1) c. Has agreed to continue adequate contraception for sexual activity that could lead to pregnancy through 6 months following study drug administration d. Is not currently breastfeeding Adequate contraception for participants assigned female sex at birth is defined as consistent and correct use of a highly effective locally approved contraceptive method in accordance with local regulations for contraceptive use in clinical trial participants. 8. Has been assigned male sex at birth with partner(s) of childbearing potential and agree to use contraception, per local regulations, through 6 months after dosing. If their partner is pregnant, males must agree to use a condom. No sperm donation is permitted through 6 months after dosing. 9. Is able to understand and comply with study requirements /procedures (if applicable, with assistance by caregiver, surrogate, or guardian/[LAR]) based on the assessment of the investigator. 10. Is able and willing to provide informed consent. An LAR may be used only in cases where inclusion criterion 9 is able to be fulfilled. In the case of adolescents, informed assent must also be obtained as required by local guidelines.