A team of researchers from Massachusetts Institute of Technology (MIT) suggests that indoor relative humidity — the moisture levels in the air compared to the total moisture the air holds at a given temperature before saturating and forming condensation — can influence the transmission of COVID-19.

Looking at early, pre-vaccination COVID-19 data alongside meteorological data obtained from more than 120 countries, the researchers suggest that COVID-19 infections and deaths were higher when indoor relative humidity levels were outside of a 40% to 60% range.

Suggesting that a relationship exists between regional outbreaks and indoor relative humidity based on the data the team analyzed, the researchers recognized that COVID-19 cases and deaths were lower when indoor relative humidity levels were within the 40% to 60% range.

“We were very skeptical initially, especially as the Covid-19 data can be noisy and inconsistent,” the researchers explained. “We thus were very thorough trying to poke holes in our own analysis, using a range of approaches to test the limits and robustness of the findings, including taking into account factors such as government intervention. Despite all our best efforts, we found that even when considering countries with very strong versus very weak Covid-19 mitigation policies, or wildly different outdoor conditions, indoor — rather than outdoor — relative humidity maintains an underlying strong and robust link with Covid-19 outcomes.”

The study, Associations between indoor relative humidity and global COVID-19 outcomes, appears in the Journal of the Royal Society Interface.

To contact the author of this article, email mdonlon@globalspec.com