Study to Evaluate the Safety and Efficacy of XAV-19 in Patients With COVID-19 Induced Moderate Pneumonia

Phase 2a: Inclusion Criteria: 1. Willing and able to provide written informed consent prior to performing study procedures 2. Male or female ≥ 18 years and ≤ 85 years 3. Hospitalized for COVID-19 4. Positive SARS-CoV-2 RT-PCR in any body specimen (nasopharynx, saliva, sputum) ≤ 10 days before enrolment 5. Evidence of pulmonary involvement (on lung examination \[rales/crackles\] and/or chest-imaging \[Chest X-ray or computed tomography\]) 6. Requiring O2 supplement ≤ 6L/min at screening 7. Requiring O2 supplementation with SpO2 ≥ 94% on O2 therapy at screening 8. First onset of COVID-19 symptoms ≤ 10 days, among fever and/or chills, headache, myalgias, cough, shortness of breath, whichever as occurred fist 9. WOCBP must have a negative urinary pregnancy test the day of inclusion 10. All sexually active male subjects must agree to use an adequate method of contraception throughout the study period and for 90 days after the last dose of study drug and agree to no sperm donation until the end of the study, or for 90 days after the last dose of XAV-19, whichever is longer 11. Patients with French social security Exclusion Criteria: 1. Evidence of multiorgan failure (severe COVID-19) 2. Mechanically ventilated (including ECMO) 3. Receipt of immunoglobulins or any blood products in the past 30 days 4. Psychiatric or cognitive illness or recreational drug/alcohol use that in the opinion of the investigator, would affect subject safety and/or compliance 5. End-stage renal disease (eGFR \< 15 ml/min/1,73 m2) 6. Child-Pugh C stage liver cirrhosis 7. Decompensated cardiac insufficiency 8. History of active drug abuse 9. Known allergy, hypersensitivity, or intolerance to the study drug, or to any of its components 10. Females of childbearing potential without contraceptive method, or with positive pregnancy test, breastfeeding, or planning to become pregnant during the study period 11. Current documented and uncontrolled bacterial infection. 12. Prior severe (grade 3) allergic reactions to plasma transfusion 13. Patient participating in another interventional clinical trial 14. Life expectancy estimated to be less than 6 months 15. Patient under guardianship or trusteeship Phase 2b: Inclusion criteria: 1. Willing and able to provide written informed consent prior to performing study procedures 2. Male or female ≥ 18 years 3. Hospitalized for COVID-19 4. Documentation of SARS-Cov-2 infection before enrolment, by positive SARS-CoV-2 RT-PCR or antigen in any body specimen (nasopharynx, oropharynx, saliva, sputum, bronchoalveolar lavage …) before enrolment 5. Evidence of pulmonary involvement (on lung examination \[rales/crackles\] and/or chestimaging \[Chest X-ray or computed tomography\]) 6. Requiring O2 supplement ≤ 6L/min at screening 7. Requiring O2 supplementation with SpO2 ≥ 92% on O2 therapy at screening (or ≥ 90 % if chronic obstructive pulmonary disease) 8. First onset of COVID-19 symptoms ≤ 14 days, among fever and/or chills, headache, myalgias, cough, shortness of breath, whichever as occurred fist (other symptoms such as asthenia not to be considered in this list) 9. WOCBP must have a negative urinary pregnancy test the day of inclusion 10. All sexually active male subjects must agree to use an adequate method of contraception throughout the study period and for 90 days after the last dose of study drug and agree to no sperm donation until the end of the study, or for 90 days after the last dose of XAV-19, whichever is longer 11. Patients with French social security Exclusion criteria: 1. Evidence of multiorgan failure (severe COVID-19) 2. Mechanically ventilated (including ECMO) 3. Receipt of immunoglobulins or any blood products in the past 30 days 4. Psychiatric or cognitive illness or recreational drug/alcohol use that in the opinion of the investigator, would affect subject safety and/or compliance 5. End-stage renal disease (eGFR \< 15 ml/min/1,73 m2) 6. Child-Pugh C stage liver cirrhosis 7. Decompensated cardiac insufficiency 8. Known allergy, hypersensitivity, or intolerance to the study drug, or to any of its components 9. Females of childbearing potential without contraceptive method, or with positive pregnancy test, breastfeeding, or planning to become pregnant during the study period 10. Current documented and uncontrolled bacterial infection. 11. Prior severe (grade 3) allergic reactions to plasma transfusion 12. Patient participating in another interventional clinical trial 13. Life expectancy estimated to be less than 6 months 14. Patient under guardianship or trusteeship 15. Patient already included 16. Prior hospitalisation in intensive care unit for the current covid-19 episode