Statistical analysis
In stage 1, we determined that the enrolment of 168 patients would provide a power of 81% to distinguish the response rate on day 29 of the dose groups from the placebo, assuming an 80% response rate for the meplazumab groups and 50% for the placebo. Additional details regarding the calculations of the sample size and total sample size are provided in the Supplementary Note Mortality on day 29 and the proportion of patients alive and discharged without supplemental oxygen on day 29 were analysed by the Cochran-Mantel-Haenszel (CMH) test and patients were stratified according to their age group and baseline severity grade. The Changes from baseline of viral load and cytokine levels were statistically described by each group, and difference among groups were analysed statistically according to logarithmic converted ANOVA; the difference between the two groups were statistically tested using the logarithmic converted group t-test. Qualitative results of viral load were summarized by each group, and the difference among groups were statistically tested according to Chi-square Test or Fisher’s exact probability method. The negative conversion rate and the corresponding 95% confidence interval were calculated by Kaplan–Meier method (Greenwood method: log-log transformation) for each group.All the statistical analyses were carried out by Statistical Analysis System (SAS) software, version 9.4 or higher (SAS Institute). The statistical analysis methods have been described in the Supplementary Note 