Before revision:  we calculate the daily effective reproductive number, R, for each of all 100 Chinese cities with more than 40 cases . Using the daily R values from January 21 to 23,2020 as proxies of non-intervened transmission intensity, we find, under a linear regression framework, high temperature and high humidity significantly reduce the transmission of COVID-19 , respectively.
After revision:  we calculate the daily effective reproductive number, R, for each of all 100 Chinese cities , and cases with confirmed dates from March 15 to April 25 for 1,005 U.S. counties. Statistical analysis is performed to assess the relationship between the transmissibility of COVID-19 and the temperature/humidity, by controlling for various demographic, socio-economic, geographic, healthcare and policy factors and correcting for cross-sectional correlation. We find a similar influence of the temperature and relative humidity on effective reproductive number (R values) of COVID-19 , respectively.