- clinical signs indicative of covid-19 illness requiring hospitalization, defined as any of the following: shortness of breath at rest, respiratory rate ≥30, heart rate ≥125, peripheral capillary oxygen saturation ≤93% on room air - treatment with a therapeutic agent against sars-cov-2 including, but not limited to, other direct acting antivirals, convalescent plasma, monoclonal antibodies against sars cov-2, or intravenous immunoglobulin within 3 months or less than 5 drug elimination half-lives (whichever is longer) prior to screening - requirement, in the opinion of the investigator, for any of the prohibited medications during the study - use of hydroxychloroquine or amiodarone within 7 days of screening - pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of at-527. women of childbearing potential must have a negative urine pregnancy test result at screening - abnormal laboratory test results at screening - clinically significant abnormal ecg, as determined by the investigator, at screening - planned procedure or surgery during the study - known allergy or hypersensitivity to study drug or drug product excipients - substance abuse, as determined by the investigator, within 12 months prior to screening - poor peripheral venous access - malabsorption syndrome or other condition that would interfere with enteral absorption - any clinically significant history of epistaxis within the last 3 months and/or history of being hospitalized due to epistaxis of any previous occasion - history of anaphylaxis - any uncontrolled serious medical condition or other clinically significant abnormality in clinical laboratory tests that, in the investigator's judgment, precludes the patient's safe participation in and completion of the study

- clinical signs indicative of covid-19 illness requiring hospitalization, defined as any of the following: shortness of breath at rest, respiratory rate ≥30, heart rate ≥125, peripheral capillary oxygen saturation ≤93% on room air - treatment with a therapeutic agent against sars-cov-2 including, but not limited to, other direct acting antivirals, convalescent plasma, monoclonal antibodies against sars cov-2, or intravenous immunoglobulin within 3 months or less than 5 drug elimination half-lives (whichever is longer) prior to screening - requirement, in the opinion of the investigator, for any of the prohibited medications during the study - use of hydroxychloroquine or amiodarone within 7 days of screening - pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of at-527. women of childbearing potential must have a negative urine pregnancy test result at screening - abnormal laboratory test results at screening - clinically significant abnormal ecg, as determined by the investigator, at screening - planned procedure or surgery during the study - known allergy or hypersensitivity to study drug or drug product excipients - substance abuse, as determined by the investigator, within 12 months prior to screening - poor peripheral venous access - malabsorption syndrome or other condition that would interfere with enteral absorption - any clinically significant history of epistaxis within the last 3 months and/or history of being hospitalized due to epistaxis of any previous occasion - history of anaphylaxis - any uncontrolled serious medical condition or other clinically significant abnormality in clinical laboratory tests that, in the investigator's judgment, precludes the patient's safe participation in and completion of the study

- clinical signs indicative of covid-19 illness requiring hospitalization, defined as any of the following: shortness of breath at rest, respiratory rate ≥30, heart rate ≥125, peripheral capillary oxygen saturation ≤93% on room air - presence of any of the following risk factors for severe covid-19 illness: obesity (body mass index ≥30 kg/m2), chronic kidney disease, chronic obstructive pulmonary disease, asthma, heart conditions (e.g., heart failure, coronary artery disease, cardiomyopathies), hypertension, diabetes, liver disease, hematological disorders, or immunosuppression - treatment with a therapeutic agent against sars-cov-2 including, but not limited to, other direct acting antivirals, convalescent plasma, monoclonal antibodies against sars cov-2, or intravenous immunoglobulin within 3 months or less than 5 drug elimination half-lives (whichever is longer) prior to screening - concurrent infection requiring systemic antiviral or antibacterial therapy at screening - requirement, in the opinion of the investigator, for any of the prohibited medications during the study - use of hydroxychloroquine or amiodarone within 7 days of screening - pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of at-527. women of childbearing potential must have a negative urine pregnancy test result at screening - planned procedure or surgery during the study - active cancer at any site - history of organ transplant - known history of hepatitis c - known history of hepatitis b - known hiv infection - known allergy or hypersensitivity to study drug or drug product excipients - current smoker, or former smoker with a smoking history of ≥10 pack-years - substance abuse, as determined by the investigator, within 12 months prior to screening - poor peripheral venous access - malabsorption syndrome or other condition that would interfere with enteral absorption - for cohorts b-e only: active psychiatric disease requiring treatment, or history of any psychiatric disorder, which, in the investigator's judgment, could deteriorate during the 14 day residential stay period of the study - any clinically significant history of epistaxis within the last 3 months and/or history of being hospitalized due to epistaxis of any previous occasion - history of anaphylaxis - any serious medical condition or abnormality in clinical laboratory tests that, in the investigator's judgment, precludes the patient's safe participation in and completion of the study

- clinical signs indicative of covid-19 illness requiring hospitalization, defined as any of the following: shortness of breath at rest, respiratory rate ≥30, heart rate ≥125, peripheral capillary oxygen saturation ≤93% on room air - presence of any of the following risk factors for severe covid-19 illness: obesity (body mass index ≥30 kg/m2), chronic kidney disease, chronic obstructive pulmonary disease, asthma, heart conditions (e.g., heart failure, coronary artery disease, cardiomyopathies), hypertension, diabetes, liver disease, hematological disorders, or immunosuppression - treatment with a therapeutic agent against sars-cov-2 including, but not limited to, other direct acting antivirals, convalescent plasma, monoclonal antibodies against sars cov-2, or intravenous immunoglobulin within 3 months or less than 5 drug elimination half-lives (whichever is longer) prior to screening - concurrent infection requiring systemic antiviral or antibacterial therapy at screening - requirement, in the opinion of the investigator, for any of the prohibited medications during the study - use of hydroxychloroquine or amiodarone within 7 days of screening - pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of at-527. women of childbearing potential must have a negative urine pregnancy test result at screening - planned procedure or surgery during the study - active cancer at any site - history of organ transplant - known history of hepatitis c - known history of hepatitis b - known hiv infection - known allergy or hypersensitivity to study drug or drug product excipients - current smoker, or former smoker with a smoking history of ≥10 pack-years - substance abuse, as determined by the investigator, within 12 months prior to screening - poor peripheral venous access - malabsorption syndrome or other condition that would interfere with enteral absorption - for cohorts b-e only: active psychiatric disease requiring treatment, or history of any psychiatric disorder, which, in the investigator's judgment, could deteriorate during the 14 day residential stay period of the study - any clinically significant history of epistaxis within the last 3 months and/or history of being hospitalized due to epistaxis of any previous occasion - history of anaphylaxis - any serious medical condition or abnormality in clinical laboratory tests that, in the investigator's judgment, precludes the patient's safe participation in and completion of the study