Clinical severity scoring We classified our patients into 3 groups according to the COVID-19 severity stratification by the World Health Organisation [16] into the following: (i) a mild-disease group that included symptomatic patients without evidence of viral pneumonia or hypoxia, (ii) a moderate disease group that had clinical signs of pneumonia such as fever, cough, dyspnea, fast breathing but no signs of severe pneumonia, including SpO2 ≥ 90% on room air [17], and (iii) a severe disease group who presented with clinical signs of pneumonia plus one of the following: respiratory rate > 30 breaths / min, severe respiratory distress, or SpO2 < 90% on room air.