Coronavirus and humidity: Number of cases rise as air gets drier, study shows


Doctor: “Accumulating evidence shows that climate is a factor in COVID-19 spread, raising the prospect of seasonal disease outbreaks.”


SYDNEY – Since the start of the coronavirus pandemic, studies show a link between climate and the spread of COVID-19. One of these studies links drier air to higher rates of transmission. Now, a second study confirms this finding, adding to the evidence that the weather is a key factor in this crisis. Researchers at the University of Sydney find the number of COVID-19 cases rise greatly for every percent the humidity drops.

The Australian researchers are focusing on the relationship between various climate factors and virus cases in New South Wales. They estimate that, for every one-percent decrease in relative humidity, there is a seven to eight-percent increase in COVID-19 cases.

“Dry air appears to favor the spread of COVID-19, meaning time and place become important,” says Dr. Michael Ward in a university statement. “Accumulating evidence shows that climate is a factor in COVID-19 spread, raising the prospect of seasonal disease outbreaks.”

As Ward explains, there are a few biological factors contributing to the link between humidity and virus transmission.

“When the humidity is lower, the air is drier and it makes the aerosols smaller,” the professor at the Sydney School of Veterinary Science adds. “When you sneeze and cough those smaller infectious aerosols can stay suspended in the air for longer. That increases the exposure for other people. When the air is humid and the aerosols are larger and heavier, they fall and hit surfaces quicker.”

“This suggests the need for people to wear a mask, both to prevent infectious aerosols escaping into the air in the case of an infectious individual, and exposure to infectious aerosols in the case of an uninfected individual,” Ward concludes.

The study is published in Transboundary and Emerging Diseases.

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