1. Requiring hospitalization at time of screening, or at time of study drug administration. 2. Oxygen saturation (SpO2) = 93% on room air at sea level or ratio of arterial oxygen partial pressure (PaO2 in mmHg) to fractional inspired oxygen (FiO2) < 300, respiratory rate = 30 per minute, and heart rate = 125 per minute. 3. Known allergies to any of the components used in the formulation of the ensovibep or placebo. 4. Suspected or proven serious, active bacterial, fungal, viral, or other infection (besides SARS-CoV-2) that in the opinion of the investigator could constitute a risk when taking intervention. 5. Any serious concomitant systemic disease, condition, or disorder that, in the opinion of the investigator, should preclude participation in this study. 6. Any co-morbidity requiring surgery within 7 days of dosing, or that is considered life-threatening within 29 days of dosing. 7. Prior or concurrent use of any medication for treatment of COVID-19, including antiviral agents, convalescent serum, or anti-viral antibodies. Purely symptomatic therapies (e.g., over-the-counter [OTC] cough medications, acetaminophen, and nonsteroidal anti-inflammatories [NSAIDs]) are permitted. Prior vaccination for COVID-19 is permitted.

1. Requiring hospitalization at time of screening, or at time of study drug administration. 2. Oxygen saturation (SpO2) = 93% on room air at sea level or ratio of arterial oxygen partial pressure (PaO2 in mmHg) to fractional inspired oxygen (FiO2) < 300, respiratory rate = 30 per minute, and heart rate = 125 per minute. 3. Known allergies to any of the components used in the formulation of the ensovibep or placebo. 4. Suspected or proven serious, active bacterial, fungal, viral, or other infection (besides SARS-CoV-2) that in the opinion of the investigator could constitute a risk when taking intervention. 5. Any serious concomitant systemic disease, condition, or disorder that, in the opinion of the investigator, should preclude participation in this study. 6. Any co-morbidity requiring surgery within 7 days of dosing, or that is considered life-threatening within 29 days of dosing. 7. Prior or concurrent use of any medication for treatment of COVID-19, including antiviral agents, convalescent serum, or anti-viral antibodies. Purely symptomatic therapies (e.g., over-the-counter [OTC] cough medications, acetaminophen, and nonsteroidal anti-inflammatories [NSAIDs]) are permitted. Prior vaccination for COVID-19 is permitted.