Yu et al [56]. Retrospective study HCQ group: n = 48; no-HCQ group: n = 502 HCQ (200 mg/2 times/day, for 7 to 10 days) The fatalities of HCQ group was significantly lower than no-HCQ group. HCQ treatment was related to significantly reduced mortality in critically ill COVID-19 patients and greatly lowered IL-6 level. Mortality was used as a measure of outcome and the study included critically ill patients. Retrospective design of the study and the number of HCQ group patients was small.