Statistical methods
Quantitative variables are expressed as mean ± standard deviation when normally distributed and median (IQR) otherwise. Normality was tested using the Shapiro test. Categorical variables are expressed as absolute (relative, %) frequencies.Analysis of the primary objective was reported by treatment arm and performed in both intentions to treat and eligible (“per protocol”) populations. Secondary objectives were only analyzed per protocol.To compare the main study variable, proportion of patients that reached an OSCI grade of 5 or higher, between control and treated group an homogeneity test was performed with the Chi-squared statistic.To compare the study variable SpFiO2 worsening below 300 and clinical improvement between study arms, the Chi-squared test was performed. Fisher's exact test was used for the analysis of the categorical variables clinical worsening, SpFiO2 recovery, number of patients requiring ICU admission and mortality rates at 28 days, 6 months and 12 months.For the continuous variables time to SpFiO2 worsening (< 300), time to clinical improvement, time from randomization to discharge and time to lymphocyte recovery, the Mann-Whitney U test was performed. The t-student test was used for time to SpFiO2 recovery.