Reduced humidity linked to increased COVID-19 risk

https://www.eurekalert.org/pub_releases/2020-06/uos-ccb060120.php

News Release 1-Jun-2020
COVID-19 could be a seasonal illness
University of Sydney


A study conducted in Sydney during the early epidemic stage of COVID-19 has found an association between lower humidity and an increase in locally acquired positive cases. Researchers discovered a 1 percent decrease in humidity could increase the number of COVID-19 cases by 6 percent.

The research led by Professor Michael Ward, an epidemiologist in the Sydney School of Veterinary Science at the University of Sydney, and two researchers from our partner institution Fudan University School of Public Health in Shanghai, China, is the first peer-reviewed study of a relationship between climate and COVID-19 in the southern hemisphere.

"COVID-19 is likely to be a seasonal disease that recurs in periods of lower humidity. We need to be thinking if it's winter time, it could be COVID-19 time," said Professor Ward.

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"When it comes to climate, we found that lower humidity is the main driver here, rather than colder temperatures," Professor Ward said. "It means we may see an increased risk in winter here, when we have a drop in humidity. But in the northern hemisphere, in areas with lower humidity or during periods when humidity drops, there might be a risk even during the summer months. So vigilance must be maintained."

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Professor Ward said there are biological reasons why humidity matters in transmission of airborne viruses.

"When the humidity is lower, the air is drier and it makes the aerosols smaller," he said. "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."

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