Inclusion Criteria:  Age 18 years or older Currently admitted to hospital There is a positive sample for COVID-19 within the past 21 days. The sample can be a nasal or pharyngeal swab, sputum, tracheal aspirate, bronchoalveolar lavage, or another sample from the patient Modified ordinal clinical scale 4-5  Exclusion Criteria:  Intubated and on mechanical ventilation, or requiring immediate intubation as per the treating clinician's assessment Heparin allergy or heparin-induced thrombocytopaenia Activated partial thromboplastin time (APTT) > 120 seconds, not due to anticoagulant therapy and does not correct with administration of fresh frozen plasma Platelet count < 20 x 109 per L Pulmonary bleeding or uncontrolled bleeding Pregnant or might be pregnant Acute brain injury that may result in long-term disability Myopathy, spinal cord injury, or nerve injury or disease with a likely prolonged incapacity to breathe independently e.g. Guillain-Barre syndrome Treatment limitations in place, i.e. not for intubation, not for ICU admission Death is imminent or inevitable within 24 hours Clinician objection Refusal of participant consent