Clinical signs indicative of COVID-19 illness requiring hospitalization Admitted to a hospital prior to randomization or is hospitalized (inpatient) at randomization due to COVID-19 In the opinion of the investigator, is likely to experience imminent deterioration and require hospitalization Treatment with an investigational drug within 5 half-lives or 3 months (whichever is longer) of randomization Treatment with a COVID-19 therapeutic agent against SARS-CoV-2 including, but not limited to, other direct or indirect acting antivirals against SARS CoV 2 (such as remdesivir or favipiravir), systemic or inhaled steroids (such as dexamethasone or inhaled budesonide), colchicine, ivermectin, interferons, convalescent plasma, monoclonal antibodies against SARS CoV-2 or Interleukin 6 (IL-2) intravenous immunoglobulin or other emergency use authorization (EUA)-approved treatments within 3 months or less than 5 drug elimination half-lives (whichever is longer) prior to the screening visit Concomitant use of P-glycoprotein (P-gp) inhibitors or inducers Known allergy or hypersensitivity to components of study drug Pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of RO7496998 (AT-527) Abnormal laboratory test results at screening Requirement of any prohibited medications during the study Other known active viral or bacterial infection at the time of screening, such as influenza. This exclusion does not apply to patients with stable chronic viral infections, such as chronic HCV or HIV providing other eligibility criteria are met Any clinically significant medical condition or laboratory abnormality that, in the opinion of the investigator, could jeopardize the safety of the patient or affect patient compliance or safety/efficacy observations during the study COVID 19 vaccination within <=40 days prior to enrollment (second dose if applicable)

Clinical signs indicative of COVID-19 illness requiring hospitalization Admitted to a hospital prior to randomization or is hospitalized (inpatient) at randomization due to COVID-19 In the opinion of the investigator, is likely to experience imminent deterioration and require hospitalization Treatment with an investigational drug within 5 half-lives or 3 months (whichever is longer) of randomization Treatment with a COVID-19 therapeutic agent against SARS-CoV-2 including, but not limited to, other direct or indirect acting antivirals against SARS CoV 2 (such as remdesivir or favipiravir), systemic or inhaled steroids (such as dexamethasone or inhaled budesonide), colchicine, ivermectin, interferons, convalescent plasma, monoclonal antibodies against SARS CoV-2 or Interleukin 6 (IL-2) intravenous immunoglobulin or other emergency use authorization (EUA)-approved treatments within 3 months or less than 5 drug elimination half-lives (whichever is longer) prior to the screening visit Concomitant use of P-glycoprotein (P-gp) inhibitors or inducers Known allergy or hypersensitivity to components of study drug Pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of RO7496998 (AT-527) Abnormal laboratory test results at screening Requirement of any prohibited medications during the study Other known active viral or bacterial infection at the time of screening, such as influenza. This exclusion does not apply to patients with stable chronic viral infections, such as chronic HCV or HIV providing other eligibility criteria are met Any clinically significant medical condition or laboratory abnormality that, in the opinion of the investigator, could jeopardize the safety of the patient or affect patient compliance or safety/efficacy observations during the study COVID 19 vaccination within <=40 days prior to enrollment (second dose if applicable)

Clinical signs indicative of COVID-19 illness requiring hospitalization Admitted to a hospital prior to randomization or is hospitalized (inpatient) at randomization due to COVID-19 In the opinion of the investigator, is likely to experience imminent deterioration and require hospitalization Treatment with an investigational drug within 5 half-lives or 30 days (whichever is longer) of randomization Treatment with a COVID-19 therapeutic agent against SARS-CoV-2 including, but not limited to, other direct or indirect acting antivirals, dexamethasone, interferons, convalescent plasma, monoclonal antibodies against SARS CoV-2, intravenous immunoglobulin or other emergency use authorization (EUA)-approved treatments within the last 2 weeks prior to the screening visit Concomitant use of P-glycoprotein (P-gp) inhibitors or inducers Known allergy or hypersensitivity to components of study drug Pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of RO7496998 (AT-527) Abnormal laboratory test results at screening Requirement of any prohibited medications during the study Known active viral or bacterial infection at the time of screening Any clinically significant medical condition or laboratory abnormality that, in the opinion of the investigator, could jeopardize the safety of the patient or affect patient compliance or safety/efficacy observations during the study

Clinical signs indicative of COVID-19 illness requiring hospitalization Admitted to a hospital prior to randomization or is hospitalized (inpatient) at randomization due to COVID-19 In the opinion of the investigator, is likely to experience imminent deterioration and require hospitalization Treatment with an investigational drug within 5 half-lives or 30 days (whichever is longer) of randomization Treatment with a COVID-19 therapeutic agent against SARS-CoV-2 including, but not limited to, other direct or indirect acting antivirals, dexamethasone, interferons, convalescent plasma, monoclonal antibodies against SARS CoV-2, intravenous immunoglobulin or other emergency use authorization (EUA)-approved treatments within the last 2 weeks prior to the screening visit Concomitant use of P-glycoprotein (P-gp) inhibitors or inducers Known allergy or hypersensitivity to components of study drug Pregnant or breastfeeding, or intending to become pregnant during the study or within 30 days after the final dose of RO7496998 (AT-527) Abnormal laboratory test results at screening Requirement of any prohibited medications during the study Known active viral or bacterial infection at the time of screening Any clinically significant medical condition or laboratory abnormality that, in the opinion of the investigator, could jeopardize the safety of the patient or affect patient compliance or safety/efficacy observations during the study