COVID-19 mortality in ICUs associated with critical care staffing. Issue 1 (20th April 2021) - Xi, Jingjing; Zeng, Lin; Li, Shusheng; Ai, Yuhang; He, Xiandi; Kang, Yan; Li, Yimin; Mo, Yanping; Peng, Yue; Qian, Kejian; Qin, Bingyu; Wang, Chunting; et al.