The association between low humidity and increased disease from SARS-CoV-2 is real, important, and cannot be discounted by the presence of other variables.
Is today a good day for grocery shopping? Check your weather app to help you decide whether or not you may be putting yourself in harm's way. Microbiologists, epidemiologists, and infectious disease clinicians are continuing to collect data showing that low humidity significantly increases viral transmission and COVID-19 illness.
The most relevant humidity measurement for health is indoor relative humidity (RH) for several reasons. First, we spend most of our time indoors. Secondly, RH denotes the difference between how much moisture the air can possibly hold at a given temperature versus how much water vapor is actually in the air. This is key because this water vapor “deficit” indicates the evaporative forces on any source of moisture, such as juicy human beings, in that space.