Study of Obeldesivir in Children and Adolescents With COVID-19

Key Inclusion Criteria: * Individual or legal guardian willing and able to provide written informed consent prior to performing study procedures. Individuals will provide assent, if possible, in accordance with local requirements and investigator's discretion. * Aged \< 18 years who meet one of the following weight criteria and gestational age (GA) criteria where applicable: * Cohort 1: ≥ 6 years to \< 18 years and weight ≥ 40 kg * Cohort 2: ≥ 6 years to \< 18 years and weight ≥ 20 kg to \< 40 kg * Cohort 3: ≥ 2 years to \< 18 years and weight ≥ 12 kg to \< 20 kg * Cohort 4: ≥ 28 days to \< 18 years and weight ≥ 3 kg to \< 12 kg * Cohort 5: ≥ 14 days to \< 28 days of age, GA ≥ 37 weeks and weight ≥ 2.5 kg * Cohort 6: 0 days to \< 14 days of age, GA ≥ 37 weeks and birth weight ≥ 2.5 kg * Cohort 7: 0 days to \< 56 days of age, GA \< 37 weeks and birth weight ≥ 1.5 kg * Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection confirmed by polymerase chain reaction (PCR) or an alternative molecular diagnostic assay ≤ 5 days before screening. * Initial onset of coronavirus disease 2019 (COVID-19) signs/symptoms ≤ 5 days before screening with ≥ 1 sign/symptom such as fever, cough, fatigue, shortness of breath, sore throat, headache, myalgia/arthralgia present at screening. * Presence of ≥ 1 characteristic or underlying medical condition associated with an increased risk of developing severe illness due to COVID-19 per protocol. Key Exclusion Criteria: * Anticipated access to and use of authorized or approved COVID-19 therapies during the current COVID-19 illness \< 5 days after screening (therapies including but not limited to nirmatrelvir/ritonavir, molnupiravir, intravenous remdesivir (RDV), monoclonal antibodies). * Vaccination for SARS-CoV-2 or self-reported history of SARS-CoV-2 infection \< 4 months prior to screening. * Received any approved, authorized, or investigational direct acting antiviral drug against SARS-CoV-2 for the treatment of COVID-19 \< 28 days or \< 5 half-lives, whichever is longer, before enrollment. Note: Other protocol defined Inclusion/Exclusion criteria may apply.