PBI-0451 (Pomotrelvir) Phase 2 Study in Nonhospitalized Symptomatic Adults With COVID-19

Following randomization on Day 1, subjects will complete baseline assessments prior to receiving their first dose of study drug (PBI-0451 or placebo). Randomization will be stratified as follows: * SARS-CoV-2 positive direct test diagnosis ≤ 3 days (target 30%) versus \> 3 days from first onset of COVID-19 symptom(s) ≤ 5 days prior to randomization * Received primary vaccination series, alone versus any booster shots * PK substudy participation versus nonparticipation Study drug will be taken with food, approximately 12 hours between doses, at approximately the same time for each BID dose for the remainder of the 5 days of treatment.All subjects will have additional safety and efficacy assessments during the 28-day study period. A follow-up visit (eg, telephone visit, virtual visit, clinic visit, etc. as convenient) will be conducted at Week 24 (± 20 days) after the last dose of study drug for all subjects. Information regarding ongoing or recurrent COVID-19 symptoms, survival status, pregnancy status (for female subjects of childbearing potential and female partners of male subjects), and any hospitalizations or acute/critical care visits (eg, non-admitted hospital or other care facility)that have occurred since the last study visit will be collected. A team of medically qualified individuals, including but not limited to, the Sponsor and the CRO Medical Monitors, and the Drug Safety Consultant are responsible for ongoing review of all AEs, concomitant medications, laboratory values (including virology), and vital signs (including pulse oximetry), worsening of symptoms (COVID-19 symptom questionnaire, including dyspnea), acute/critical care visits (eg, nonadmitted hospital or other care facility), and study drug discontinuations, at a minimum monthly basis throughout the study, per the Safety Monitoring Plan. Subjects who experience severe COVID-19 illness (defined in this study as sustained pulse oximetry \<94%, a respiratory rate of \>30 breaths/min, or dyspnea that requires medical attention) should discontinue study drug and be immediately referred by the Investigator to emergency care or treated by the Investigator for standard of care treatment of symptoms including, but not limited to, other antivirals, supplemental oxygen, corticosteroids, Janus kinase inhibitors, or interleukin-6 blockers, in accordance with the NIH Treatment Guidelines (NIH 2022). The subject should continue participation in the study, with study drug discontinued, for safety follow-up and clinical outcome of the medically attended visit.