Drier air has been shown to increase the transmission risk of the coronavirus. A March 2020 study found that higher humidity and higher temperatures reduced the transmission of the virus. The researchers emphasized that weather factors alone could not stop the epidemic from reaching a critical point, making measures such as social distancing ”crucial to block the transmission of COVID-19 even in summer.”
An August 2020 study in Australia found that “a decrease in relative humidity of 1% was associated with an increase in cases of 7–8%.” At lower humidity levels, infectious viral particles stay suspended in the air for longer. Previous research has shown that the transmission of SARS and MERS (other respiratory viruses) is also impacted by humidity.
The dehumidifying effects of indoor heating add to the risks of transmission in enclosed spaces in wintertime.