A Study of Secutrelvir in Participants With Coronavirus Disease 2019 (COVID-19) Who Are at High Risk for Progression to Severe Disease

Key Inclusion Criteria: * Must be 12 to \<18 years of age (where permitted by local regulations) with a body weight ≥40 kilograms, or ≥18 years of age regardless of body weight, at the time of signing the informed consent form. * Presence of risk factors for progression to severe COVID-19 at the time of screening. * Must have ≥1 COVID-19 signs/symptoms that are at least mild in severity, and the symptoms must still be present in the 24 hours prior to randomization. * Confirmed SARS-CoV-2 infection, as determined by any SARS-CoV-2 test (for example, quantitative reverse transcription polymerase chain reaction, antigen test) approved according to local regulations, of any respiratory tract specimen (for example, oropharyngeal, nasopharyngeal or nasal swab, or saliva), collected ≤72 hours prior to randomization. * Must be randomized within 72 hours of symptom onset, defined as the time when the first COVID-19 symptom occurs. * Contraceptive use by women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies. * A women of childbearing potential must have a negative urine pregnancy test within 24 hours prior to receiving the investigational intervention. * Unable or unwilling to take other locally available COVID-19 antivirals (for example, nirmatrelvir/ritonavir, molnupiravir, remdesivir, ensitrelvir). Key Exclusion Criteria: * Planned \>24 hours hospitalization for any medical procedure through Day 28. * Documented respiratory infection (for example, influenza, respiratory syncytial virus) other than COVID-19 within the 14 days prior to the screening visit. * Known history of cirrhosis or liver decompensation (including ascites, variceal bleeding, or hepatic encephalopathy). * Known history of any of the following abnormalities in the following clinical laboratory tests (within 6 months prior to the screening visit): * Total bilirubin ≥2\*upper limit of normal (ULN) (except for Gilbert's syndrome) * Aspartate aminotransferase or alanine aminotransferase ≥3\*ULN * Suspected or confirmed COVID-19 unrelated to the current episode within 6 months prior to randomization or, for moderately immunocompromised participants, within 3 months prior to randomization. * Suspected or confirmed concurrent active systemic infection other than COVID-19 that may interfere with the evaluation of response to the investigational intervention. * Ongoing long COVID-19 or post-acute sequelae of COVID-19 diagnosis. * Current severely immunocompromised conditions. * Received any other COVID-19-specific therapies within the following timeframes: * Antiviral agents (for example, remdesivir, nirmatorelvir/ritonavir, molnupiravir, ensitrelvir) within 30 days or 5 half-lives (whichever is longer) prior to randomization * Anti-SARS-CoV-2 monoclonal antibodies and COVID-19 convalescent plasma within 6 months prior to randomization Note: Other protocol-define criteria apply