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 (SpO2) <= 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 3 months of screening Pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of study drug. Women of childbearing potential must have a negative serum 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 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 (SpO2) <= 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 3 months of screening Pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of study drug. Women of childbearing potential must have a negative serum 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 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 (SpO2) <= 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 serum 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 (SpO2) <= 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 serum 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