Virus spreads faster when air is dry, researchers find

One more health benefit of living by the damp sea? – Owl

Bernard Lagan, Sydney 

A study has found that during Sydney’s peak of coronavirus in March and April more people caught the virus on days when the air was dry. When the city’s air was more humid, fewer people contracted the virus.

The authors of the peer-reviewed study, published in Transboundary and Emerging Diseases, say that dry air increases the virus’s ability to spread. In Sydney a 1 per cent decrease in the amount of water in the air was associated with a 7.7 per cent increase in Covid-19 infections.

Michael Ward, an epidemiologist at the University of Sydney and co-author of the study, told Sydney Morning Herald: “Every time we look at it we find humidity is linked with cases. And we cannot really explain that any other way.”

The same trend has been found in a study of China’s Covid-19 outbreak and the coronaviruses that caused the Sars and Mers respiratory diseases.

The researchers gathered postcode data from 1,203 local infections between February and May and correlated it with readings from weather stations.

A study in China found that for each 1 per cent increase in relative humidity on a cold day, new Covid-19 infections fell by between 11 per cent and 22 per cent. Droplets shrink in dry air, which allows them to “get further down the respiratory tract”, Tony Cunningham, of the Centre for Virus Research in Sydney, said.

Philip Russo, president of the Australasian College for Infection Prevention and Control, said that “humidity and temperature also influence behaviour regarding crowding, indoor versus outdoor activity, ventilation etc”.