A Study to Learn About the Study Medicine Ibuzatrelvir in Adults With COVID-19 Who Are Severely Immunocompromised

This is a Phase 3, randomized, actively controlled, double-blinded, double-dummy, superiority study to evaluate the efficacy and safety of ibuzatrelvir alone and in combination with remdesivir IV compared to remdesivir IV alone for the treatment of symptomatic COVID-19 in severely immunocompromised adult participants who are non-hospitalized or are hospitalized for observation or study intervention administration but do not require supplemental oxygen for COVID-19.

Inclusion Criteria: 1. 18 years of age or older at screening who are non-hospitalized or hospitalized for observation or with the intent of administering the study intervention. 2. Confirmed SARS-CoV-2 infection as determined by RAT (or other locally approved test) collected within 2 days prior to randomization. Initial onset of symptoms attributable to COVID-19 within 5 days prior to the day of randomization and at least 1 of the specified symptoms attributable to COVID-19 present on the day of randomization. 3. Severely immunocompromised due to: * Solid organ or islet cell transplant recipient who is receiving immunosuppressive therapy; * Active hematologic malignancy (eg, chronic lymphocytic leukemia, non-Hodgkin lymphoma, multiple myeloma, acute leukemia); * Receipt of CAR-T-cell therapy or HCT either within 2 years of transplantation or who are receiving immunosuppressive therapy; * Currently receiving or recently received B-cell depleting therapies (eg, rituximab), where the immunosuppressive effect is still ongoing. Exclusion Criteria: 1. Severe COVID-19, or current need for supplemental oxygen for treatment of COVID-19. 2. Receiving dialysis or have current kidney failure (ie, eGFR consistently \