To compare COVID-19 WHO score greater than or equal to 2 (for participants with COVID-19) or Dyspnoea Management Questionnaire-30 (for participants with ARDS) breathlessness scores at 6 months. This is composite primary outcome. [6 months post randomisation ];Maximum oxygen requirement (increase or decrease) over 6 months defined as follows: - An increase in oxygen requirement will be defined by 1. Increasing oxygen flow rate or FiO2 using the same oxygen delivery device; or 2. Escalation to invasive and non-invasive mechanical ventilation/ECMO or vasopressor/ionotropic support.- A decrease in oxygen requirement will be defined as a decrease in oxygen flow rate or FiO2 using the same oxygen delivery device; or cessation of oxygen support requirement. The peak oxygen requirement (i.e. increase from that at baseline) will be recorded; irrespective of the time of occurrence up until discharge and 6 months. Likewise; the greatest decrease will also be recorded; irrespective of the time of occurrence up until discharge and 6 months.[6 months post randomisation ];Death at 6 months and end of study. This will be ascertained by assessment of medical records. [6 months post randomisation and end of study. ]

To compare COVID-19 WHO score greater than or equal to 2 (for participants with COVID-19) or Dyspnoea Management Questionnaire-30 (for participants with ARDS) breathlessness scores at 6 months. This is composite primary outcome. [6 months post randomisation ];Maximum oxygen requirement (increase or decrease) over 6 months defined as follows: - An increase in oxygen requirement will be defined by 1. Increasing oxygen flow rate or FiO2 using the same oxygen delivery device; or 2. Escalation to invasive and non-invasive mechanical ventilation/ECMO or vasopressor/ionotropic support.- A decrease in oxygen requirement will be defined as a decrease in oxygen flow rate or FiO2 using the same oxygen delivery device; or cessation of oxygen support requirement. The peak oxygen requirement (i.e. increase from that at baseline) will be recorded; irrespective of the time of occurrence up until discharge and 6 months. Likewise; the greatest decrease will also be recorded; irrespective of the time of occurrence up until discharge and 6 months.[6 months post randomisation ];Death at 6 months and end of study. This will be ascertained by assessment of medical records. [6 months post randomisation and end of study. ]