Effects of temperature variation and humidity on the mortality of COVID-19 in Wuhan

Yueling Ma; Yadong Zhao; Jiangtao Liu; Xiaotao He; Bo Wang; Shihua Fu; Jun Yan; Jingping Niu; Bin Luo

Researchers confirmed that respiratory infection was enhanced during unusually cold and low humidity conditions [38] , indicating low humidity may be also an important risk factor for respiratory diseases. Worse, a study with data of more than 25 years found that humidity was an important determinant of mortality and low-humidity levels may cause a large increase in mortality rates, potentially by influenza-related mechanisms [39] , similar to a study carried out in the United States [40] . Consistent to these finding, our results also indicated that the risk of dying from COVID-19 decreased only with absolute humidity increasing. Breathing dry air could cause epithelial damage and/or reduction of mucociliary clearance, and then lead to render the host more susceptible to respiratory virus infection; The formation of droplet nuclei is essential to transmission, but exhaled respiratory droplets settle very rapidly at high humidity so that it is hard to contribute to influenza virus spread [41] . Moreover, the transmission of pandemic influenza virus is the most efficient under cold, dry conditions [42] , and influenza virus survival rate increased markedly in accordance with decreasing of absolute humidity [43] , which may be similar to coronavirus. Therefore, the increase of COVID-19 mortality may also be related to the lower humidity in winter.