Plerixafor in Acute Respiratory Distress Syndrome Related to COVID-19 (Phase IIb)

Inclusion Criteria: * Male or female ≥ 18 years of age, * Using contraceptive consistent with local regulations regarding the methods of contraception for those participating in clinical studies * Willing and able to provide written informed consent (or provided by legally acceptable representative if he/she is present and if in line with local regulations), * Admitted in ICU within 48 hours before randomization for COVID-19 related respiratory failure. (ICU or equivalent medical structure according to country specificities e.g., Acute Respiratory Care Unit, High Dependency Care Unit if they can provide: continuous IV infusion,continuous ECG, respiratory rate, percutaneous oxygen saturation screen monitoring, high flow nasal oxygen) * Not requiring immediate (within 24-36 hours) invasive mechanical ventilation according to investigator's judgment, * Confirmed pneumoniae due to SARS-CoV-2, Laboratory-confirmed SARS-CoV-2 infection as determined by RT-PCR (in nasopharynx or throat samples) or other commercial or public health assay in any specimen, performed within 2 weeks prior to randomization, * Acute respiratory failure requiring oxygen support (≥ 5L/min) to achieve a transcutaneous oxygen saturation \> 94%, * Estimated glomerular filtration rate (eGFR) \> 50 mL/min/1.73m2 by the CKD-EPI (Chronic Kidney Disease - Epidemiology Collaboration) equation. Exclusion Criteria: * Pregnancy or breast feeding, * Anticipated transfer to another hospital, which is not a study site within 72 hours of randomisation, * Need for Invasive mechanical ventilation at time of inclusion, * Evidence of uncontrolled bacterial pneumopathy or active infection other than SARS-Cov-2 (laboratory confirmation), * Primitive pulmonary arterial hypertension, * Cardio-vascular co-morbidity: * History of vascular ischemic events (myocardial infarction or stroke) or congestive heart failure or peripheral arterial disease, * History or current significant cardiac rhythm disorders (e.g., ventricular tachycardia), * Known medical history of proven symptomatic postural hypotension, * Known cancer (solid or blood) in the last 5 previous years or previous haematological disorders (malignancies and other chronic conditions) or having received bone marrow transplant, * Inadequate haematological function defined by: * Neutrophil count \< 1.0 x 109/L, * Haemoglobin \< 9.0 g/dL (90 g/L), * Platelets \< 100 x 109/L, * Kaliemia \< 3.5 mmol/L and/or total Calcemia \< 2.2 mmol/L, * Inadequate hepatic function defined by Aspartate aminotransferase (AST) and/or Alanine Aminotransferase (ALT) \> 3 x upper limit of normal (ULN) and/or Total bilirubin \> 2 x ULN, * Patients with known allergy to Plerixafor or its excipients. * Previous (within 4 weeks) or current participation in another clinical study other than an observational study. * Patients with auto immune disease treated or not,