The “sweet spot” associated with reduced COVID-19 cases and deaths is 40%-60% indoor relative humidity, an MIT news release said. People who maintained indoor relative humidity outside those parameters had higher rates of catching COVID-19.
Most people are comfortable with 30%-50% relative humidity, researchers said. An airplane cabin has about 20% relative humidity.
Relative humidity is the amount of moisture in the air, compared with the total moisture the air can hold at a given temperature before saturating and forming condensation.
The study was published in The Journal of the Royal Society Interface. Researchers examined COVID-19 data and meteorological measurements from 121 countries from January 2020 through August 2020, before vaccines became available to the public.
“When outdoor temperatures were below the typical human comfort range, they assumed indoor spaces were heated to reach that comfort range. Based on the added heating, they calculated the associated drop in indoor relative humidity,” the MIT news release said.
The research teams found that when a region reported a rise in COVID-19 cases and deaths, the region’s estimated indoor relative humidity was either lower than 40% or higher than 60%, the release said.
“There’s potentially a protective effect of this intermediate indoor relative humidity,” said Connor Verheyen, the lead author and a PhD student in medical engineering and medical physics in the Harvard-MIT Program in Health Sciences and Technology.
Widespread use of the 40%-60% indoor humidity range could reduce the need for lockdowns and other widespread restrictions, the study concluded.
“Unlike measures that depend on individual compliance (for example, masking or hand-washing), indoor RH optimization would achieve high compliance because all occupants of a common indoor space would be exposed to similar ambient conditions,” the study said. “Compared to the long timelines and high costs of vaccine production and distribution, humidity control systems could potentially be implemented more quickly and cheaply in certain indoor settings.”
A version of this article first appeared on WebMD.com.