Inclusion Criteria:  Probable or confirmed COVID-19 infection according to WHO criteria Moderate or severe COVID-19 respiratory infection according to Vietnamese guidelines Requirement for supplemental oxygen therapy  Exclusion Criteria:  Invasive mechanical ventilation, or non-invasive ventilation (NIV) with CPAP or BiPAP or imminent need for these Contraindications to prone position (see Appendix 5) Pregnancy Severe obesity (BMI >35), Altered level of consciousness (GCS <13) Attending doctor judged prone position to be unsuitable for the patient for any reason Patients in whom there is a decision that care will not be escalated Failure to have informed consent