The effect of climate
Australian research indicates that lower relative humidity favors COVID-19 infection. A reduction in relative humidity of 1% was associated with an increase of COVID-19 cases of more than 6%. Dry air is thought to increase the chances of survival and transmission of the virus via respiratory droplets and aerosols, seen so far as the main mechanisms of spread.
An effect of temperature on COVID-19 cases could not be found. A possible explanation might be that temperature in New South Wales did not drop below 16°C in the period studied.
Ward M.P., Xiao S., Zhang Z., The role of climate during the COVID-19 epidemic in New South Wales, Australia, Transbound Emerg Dis. 2020;00-1-5.