Researchers from the MIT examined the effect of temperature and humidity on the epidemiology of COVID-19 infections and published their work this week. It’s not peer-reviewed yet. They explored whether the lower number of cases in tropical countries might be due to warm humid conditions. Viruses often prefer cooler drier weather.  High temperatures combined with high absolute humidity often slow the spread of many viruses.

The researchers found that 90% of the COVID-19 illnesses occurred between 38 and 63F with dew points between 32 and 50F (which mostly occur above 30 degrees North Latitude).  They posited that the large difference in the number of cases between the Equator & 30N latitude and between 30N & 50N latitude might mean that 2019-nCoV isn’t as communicable in warmer humid climates (Phoenix’s latitude is at about 33N).

Their preliminary results suggest that both higher temperature and higher humidity (in combination) slows down the spread of the virus. The combination of both high temperatures along with higher humidity may be working together (Note: warmer air can hold a lot more water). 

Arizona typically has temperatures and humidity in the range that may slow transmission during the monsoon season. During late May and June our temps are high in the deserts, but the humidity doesn’t usually pick up until the 4th of July. We should be past peak transmission of the virus by then – but perhaps the monsoon will bring welcome additional relief.