Study of Secutrelvir in Participants With COVID-19

Key Inclusion Criteria: * Must be 12 to \< 18 years of age (where permitted by local regulation) with a body weight ≥ 40 kilograms (kg), or ≥ 18 and \< 75 years of age regardless of body weight, at the time of signing the informed consent form (ICF). * Must have ≥ 1 of the protocol-defined COVID-19 symptoms of moderate or severe, present within 24 hours prior to randomization. * Confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection as determined by any SARS-CoV-2 test, collected ≤ 48 hours prior to randomization. * Must be randomized within 48 hours of COVID-19 symptom onset, defined as the time when the first COVID-19 symptom occurs. * Agrees not to participate in another clinical study for the treatment of COVID-19 until completion of the study. Key Exclusion Criteria: * Current need or anticipated need for hospitalization within 24 hours, due to signs of severe COVID-19 illness or due to other medical conditions requiring hospitalization in the opinion of the site investigator. * Documented respiratory infection (for example, influenza, respiratory syncytial virus infection) other than COVID 19 within 14 days prior to the screening visit. * Known history of cirrhosis or liver decompensation (including ascites, variceal bleeding, or hepatic encephalopathy). * Suspected or confirmed COVID-19 outside of the current episode within 3 months of 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 or postacute sequelae of COVID (PASC) diagnosis. * Current severely immunocompromised conditions. * Received or expected to receive any other COVID-19-specific therapies. * Have previously received secutrelvir. * Exposed to an investigational drug within 30 days or 5 half-lives (whichever is longer) prior to the screening visit. Note: Other protocol-defined inclusion and exclusion criteria may apply.