Medical workers take care of a COVID-19 patient whose nucleic acid test result has turned negative in a ward at the west campus of the Union Hospital affiliated to Tongji Medical College of Huazhong University of Science and Technology in Wuhan, central China's Hubei Province, April 24, 2020. The number of COVID-19 patients in serious condition in Wuhan, the central China city once hardest hit by the epidemic, has dropped to zero, a health official said Friday. (Xinhua/Shen Bohan)

Medical worker Cheng Wei takes care of a COVID-19 patient whose nucleic acid test result has turned negative in a ward at the west campus of the Union Hospital affiliated to Tongji Medical College of Huazhong University of Science and Technology in Wuhan, central China's Hubei Province, April 24, 2020. The number of COVID-19 patients in serious condition in Wuhan, the central China city once hardest hit by the epidemic, has dropped to zero, a health official said Friday. (Xinhua/Shen Bohan)

Medical workers He Jue (L) and Ma Menglin take care of a COVID-19 patient whose nucleic acid test result has turned negative in a ward at the west campus of the Union Hospital affiliated to Tongji Medical College of Huazhong University of Science and Technology in Wuhan, central China's Hubei Province, April 24, 2020. The number of COVID-19 patients in serious condition in Wuhan, the central China city once hardest hit by the epidemic, has dropped to zero, a health official said Friday. (Xinhua/Shen Bohan)

Medical worker Zhao Xin does B-mode ultrasound check for a COVID-19 patient whose nucleic acid test result has turned negative in a ward at the west campus of the Union Hospital affiliated to Tongji Medical College of Huazhong University of Science and Technology in Wuhan, central China's Hubei Province, April 24, 2020. The number of COVID-19 patients in serious condition in Wuhan, the central China city once hardest hit by the epidemic, has dropped to zero, a health official said Friday. (Xinhua/Shen Bohan)

Medical workers Ma Menglin, Li Bo and He Jue (L to R) take care of a COVID-19 patient whose nucleic acid test result has turned negative in a ward at the west campus of the Union Hospital affiliated to Tongji Medical College of Huazhong University of Science and Technology in Wuhan, central China's Hubei Province, April 24, 2020. The number of COVID-19 patients in serious condition in Wuhan, the central China city once hardest hit by the epidemic, has dropped to zero, a health official said Friday. (Xinhua/Shen Bohan)