1. History of SARS-CoV-2 infection as determined by a molecular test (antibody, antigen, or nucleic acid) from any specimen collected within 6 months before or during the screening visit. 2. Experiencing measured fever (documented temperature >38˚C or 100.4˚F) or other signs or symptoms consistent with COVID-19. 3. Known medical history of active liver disease (other than nonalcoholic hepatic steatosis), including chronic or active hepatitis B or C infection, or primary biliary cirrhosis, ChildPugh Class B or C, or acute liver failure. 4. CKD or have known moderate to severe renal impairment. 5. Known HIV infection with viral load >400 copies/mL within the last 6 months or taking prohibited medications for HIV treatment (from known medical history within past 6 months of the screening visit) 6. Suspected or confirmed concurrent active systemic infection that may interfere with the evaluation of response to the study intervention. 7. Active cancer, requiring treatment with prohibited medication (Appendix 8) that must be administered/continued during the trial period. 8. Any comorbidity requiring hospitalization and/or surgery within 7 days prior to study entry, or that is considered life-threatening within 30 days prior to study entry, as determined by the investigator. 9. Has hypersensitivity or other contraindication to any of the components of the study intervention, as determined by the investigator. 10. Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. 11. Current or expected use of any medications or substances that are highly dependent on CYP3A4 for clearance and for which elevated plasma concentrations may be associated with serious and/or lifethreatening events during treatment and for 4 days after the last dose of PF-07321332/ritonavir. 12. Concomitant use of any medications or substances that are strong inducers of CYP3A4 are prohibited within 28 days prior to first dose of PF-07321332/ritonavir and during study treatment. 13. Has received approved, authorized, or investigational anti-SARS-CoV-2 mAb, convalescent plasma, other drugs for treatment of COVID-19, or other anti-SARS-CoV-2 biologic products within 6 months of screening. 14. Has received any SARS-CoV-2 vaccine (includes any level of vaccination) within 6 months prior to screening or is expected to receive a SARS-CoV-2 vaccine or other approved, authorized, or investigational postexposure prophylaxis treatments through Day 38. 15. Is unwilling to abstain from participating in another interventional clinical study with an investigational compound or device, including those for COVID-19 therapeutics, through the End of Study visit. 16. Previous administration with an investigational drug within 30 days (or as determined by local requirement) or 5 half lives preceding the first dose of study intervention used in this study (whichever is longer). 17. Known or prior participation in this trial or another trial involving PF-07321332. 18. Participants with known history of any of the following abnormalities in clinical laboratory tests (within 6 months of the screening visit): AST or ALT level ≥2.5 X ULN, Total bilirubin level ≥2 X ULN (≥ 3X ULN for Gilbert's syndrome), eGFR <45 mL/min/1.73 m2 within 6 months of the screening visit, using the serum creatinine-based CKD-EPI formula52 Absolute neutrophil count <1,000/mm3. Note: If the investigator suspects the participant may have any of the above laboratory values, confirmatory tests should be performed at screening to confirm eligibility before the first dose of study intervention. 19. Females who are pregnant or breastfeeding. 20. Investigator site staff or Pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

1. History of SARS-CoV-2 infection as determined by a molecular test (antibody, antigen, or nucleic acid) from any specimen collected within 6 months before or during the screening visit. 2. Experiencing measured fever (documented temperature >38˚C or 100.4˚F) or other signs or symptoms consistent with COVID-19. 3. Known medical history of active liver disease (other than nonalcoholic hepatic steatosis), including chronic or active hepatitis B or C infection, or primary biliary cirrhosis, ChildPugh Class B or C, or acute liver failure. 4. CKD or have known moderate to severe renal impairment. 5. Known HIV infection with viral load >400 copies/mL within the last 6 months or taking prohibited medications for HIV treatment (from known medical history within past 6 months of the screening visit) 6. Suspected or confirmed concurrent active systemic infection that may interfere with the evaluation of response to the study intervention. 7. Active cancer, requiring treatment with prohibited medication (Appendix 8) that must be administered/continued during the trial period. 8. Any comorbidity requiring hospitalization and/or surgery within 7 days prior to study entry, or that is considered life-threatening within 30 days prior to study entry, as determined by the investigator. 9. Has hypersensitivity or other contraindication to any of the components of the study intervention, as determined by the investigator. 10. Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. 11. Current or expected use of any medications or substances that are highly dependent on CYP3A4 for clearance and for which elevated plasma concentrations may be associated with serious and/or lifethreatening events during treatment and for 4 days after the last dose of PF-07321332/ritonavir. 12. Concomitant use of any medications or substances that are strong inducers of CYP3A4 are prohibited within 28 days prior to first dose of PF-07321332/ritonavir and during study treatment. 13. Has received approved, authorized, or investigational anti-SARS-CoV-2 mAb, convalescent plasma, other drugs for treatment of COVID-19, or other anti-SARS-CoV-2 biologic products within 6 months of screening. 14. Has received any SARS-CoV-2 vaccine (includes any level of vaccination) within 6 months prior to screening or is expected to receive a SARS-CoV-2 vaccine or other approved, authorized, or investigational postexposure prophylaxis treatments through Day 38. 15. Is unwilling to abstain from participating in another interventional clinical study with an investigational compound or device, including those for COVID-19 therapeutics, through the End of Study visit. 16. Previous administration with an investigational drug within 30 days (or as determined by local requirement) or 5 half lives preceding the first dose of study intervention used in this study (whichever is longer). 17. Known or prior participation in this trial or another trial involving PF-07321332. 18. Participants with known history of any of the following abnormalities in clinical laboratory tests (within 6 months of the screening visit): AST or ALT level ≥2.5 X ULN, Total bilirubin level ≥2 X ULN (≥ 3X ULN for Gilbert's syndrome), eGFR <45 mL/min/1.73 m2 within 6 months of the screening visit, using the serum creatinine-based CKD-EPI formula52 Absolute neutrophil count <1,000/mm3. Note: If the investigator suspects the participant may have any of the above laboratory values, confirmatory tests should be performed at screening to confirm eligibility before the first dose of study intervention. 19. Females who are pregnant or breastfeeding. 20. Investigator site staff or Pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.