Age >=18 years (regardless of weight) at the time of signing informed consent or age >=12 to <18 years (weight >=40 kilogram) at the time of signing informed consent (and assent) Ability to comply with all aspects of the study protocol, including providing samples for virology, in the opinion of the investigator At least three of the following symptoms of at least moderate (score >=2 as per COVID-19 Symptom Diary) intensity: nasal congestion or runny nose, sore throat, cough, shortness of breath, muscle or body aches, fatigue, headache, chills or sweats, feeling hot or feverish, nausea, vomiting, or diarrhea Positive severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) diagnostic test (reverse-transcriptase polymerase chain reaction [RT-PCR] or validated rapid antigen test) <=72 hours prior to randomization Symptoms consistent with mild or moderate COVID-19, as determined by the Investigator, with onset <=5 days before randomization For women of childbearing potential and girls at or beyond menarche (age >=12 to <18 years): agreement to remain abstinent (refrain from heterosexual intercourse) or use adequate contraception during the treatment period and for 30 days after the final dose of RO7496998 (AT-527)

Age >=18 years (regardless of weight) at the time of signing informed consent or age >=12 to <18 years (weight >=40 kilogram) at the time of signing informed consent (and assent) Ability to comply with all aspects of the study protocol, including providing samples for virology, in the opinion of the investigator At least three of the following symptoms of at least moderate (score >=2 as per COVID-19 Symptom Diary) intensity: nasal congestion or runny nose, sore throat, cough, shortness of breath, muscle or body aches, fatigue, headache, chills or sweats, feeling hot or feverish, nausea, vomiting, or diarrhea Positive severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) diagnostic test (reverse-transcriptase polymerase chain reaction [RT-PCR] or validated rapid antigen test) <=72 hours prior to randomization Symptoms consistent with mild or moderate COVID-19, as determined by the Investigator, with onset <=5 days before randomization For women of childbearing potential and girls at or beyond menarche (age >=12 to <18 years): agreement to remain abstinent (refrain from heterosexual intercourse) or use adequate contraception during the treatment period and for 30 days after the final dose of RO7496998 (AT-527)