1. History of hospitalization for the medical treatment of COVID-19. 2. Current need for hospitalization or anticipated need for hospitalization within 48 hours after randomization in the clinical opinion of the site investigator (see Section 8.1.2.) 3. Prior to current disease episode, any confirmed SARS-CoV-2 infection, as determined by a molecular test (antigen or nucleic acid) from any specimen collection. 4. Known medical history of active liver disease (other than nonalcoholic hepatic steatosis), including chronic or active hepatitis B or C infection, primary biliary cirrhosis, Child-Pugh Class B or C, or acute liver failure. 5. Receiving dialysis or have known moderate to severe renal impairment [ie, eGFR <45 mL/min/1.73 m2 within 6 months of the screening visit, using the serum creatinine-based CKD-EPI formula] 6. Known HIV infection with a viral load greater than 400 copies/mL or taking prohibited medications for HIV treatment from known medical history within past 6 months of the screening visit) (Appendix 8). 7. Suspected or confirmed concurrent active systemic infection other than COVID-19 that may interfere with the evaluation of response to the study intervention. 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. History of 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 life-threatening events during treatment and for 4 days after the last dose of PF-07321332/ritonavir (See Appendix 8). 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 (see Appendix 8). 13. Has received or is expected to receive convalescent COVID-19 plasma. 14. Has received or is expected to receive any dose of a SARS-CoV-2 vaccine before the Day 34 visit. 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 long-term follow-up visit. 16. Previous administration with any investigational drug or vaccine within 30 days (or as determined by the local requirement) or 5 half lives preceding the first dose of study intervention used in this study (whichever is longer). 17. Known prior participation in this trial or other trial involving PF-07321332. 18. Known history of any of the following abnormalities in clinical laboratory tests (within past 6 months of the screening visit): - AST or ALT level ≥2.5 X ULN, - Total bilirubin ≥2 X ULN (≥3 X ULN for Gilbert’s syndrome), - Absolute neutrophil count <1000/mm3. - GFR <45 mL/min/1.73 m2 within 6 months of the screening visit, using the serum creatinine-based CKD-EPI formula30 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. See Appendix 2 for more details. 19. Oxygen saturation of <92% on room air obtained at rest within 24 hours prior to randomization. Note: for a potential participant who regularly receives chronic supplementary oxygen for an underlying lung condition, oxygen saturation should be measured while on their standard home oxygen supplementation. 20. Females who are pregnant or breastfeeding. 21. 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 hospitalization for the medical treatment of COVID-19. 2. Current need for hospitalization or anticipated need for hospitalization within 48 hours after randomization in the clinical opinion of the site investigator (see Section 8.1.2.) 3. Prior to current disease episode, any confirmed SARS-CoV-2 infection, as determined by a molecular test (antigen or nucleic acid) from any specimen collection. 4. Known medical history of active liver disease (other than nonalcoholic hepatic steatosis), including chronic or active hepatitis B or C infection, primary biliary cirrhosis, Child-Pugh Class B or C, or acute liver failure. 5. Receiving dialysis or have known moderate to severe renal impairment [ie, eGFR <45 mL/min/1.73 m2 within 6 months of the screening visit, using the serum creatinine-based CKD-EPI formula] 6. Known HIV infection with a viral load greater than 400 copies/mL or taking prohibited medications for HIV treatment from known medical history within past 6 months of the screening visit) (Appendix 8). 7. Suspected or confirmed concurrent active systemic infection other than COVID-19 that may interfere with the evaluation of response to the study intervention. 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. History of 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 life-threatening events during treatment and for 4 days after the last dose of PF-07321332/ritonavir (See Appendix 8). 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 (see Appendix 8). 13. Has received or is expected to receive convalescent COVID-19 plasma. 14. Has received or is expected to receive any dose of a SARS-CoV-2 vaccine before the Day 34 visit. 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 long-term follow-up visit. 16. Previous administration with any investigational drug or vaccine within 30 days (or as determined by the local requirement) or 5 half lives preceding the first dose of study intervention used in this study (whichever is longer). 17. Known prior participation in this trial or other trial involving PF-07321332. 18. Known history of any of the following abnormalities in clinical laboratory tests (within past 6 months of the screening visit): - AST or ALT level ≥2.5 X ULN, - Total bilirubin ≥2 X ULN (≥3 X ULN for Gilbert’s syndrome), - Absolute neutrophil count <1000/mm3. - GFR <45 mL/min/1.73 m2 within 6 months of the screening visit, using the serum creatinine-based CKD-EPI formula30 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. See Appendix 2 for more details. 19. Oxygen saturation of <92% on room air obtained at rest within 24 hours prior to randomization. Note: for a potential participant who regularly receives chronic supplementary oxygen for an underlying lung condition, oxygen saturation should be measured while on their standard home oxygen supplementation. 20. Females who are pregnant or breastfeeding. 21. 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.