Statistical analysis
All analyses were conducted with IBM SPSS Statistics, version 19.0 (SPSS Institute, Chicago IL, USA). Categorical variables were conducted by the chi-square (χ2) and Fisher’s exact tests. Normally distributed variables were compared using the Student’s t-test, whereas non-normally distributed variables were conducted by the Kruskal-Wallis test. Two-sided P values of 0.05 were considered statistically significant. The time to oxygen-support requirement, virus clearance were portrayed by Kaplan–Meier plot. Associations between therapies and these outcomes were assessed by Cox proportional hazards regression.