A study conducted in Australia during the early stage of the coronavirus pandemic has found an association between lower humidity and an increase in locally acquired positive cases.
The study, which is the first peer-reviewed study of a relationship between climate and COVID-19 in the southern hemisphere and was published today in Transboundary and Emerging Diseases, found a 1 percent decrease in humidity could increase the number of COVID-19 cases by 6 percent.
“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 Michael Ward, an epidemiologist in the Sydney School of Veterinary Science at the University of Sydney who led the research, in a statement
Since the COVID-19 pandemic developed in China, Europe and North America during those regions’ winter, researchers were curious to see if there was a unique association between the virus and Australia’s late summer and early autumn.
“When it comes to climate, we found that lower humidity is the main driver here, rather than colder temperatures,” Ward explained. “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.”
According to Ward, there are also biological reasons why humidity can impact the 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.”
Scientists believe that more studies, including during the winter in the southern hemisphere, are needed to confirm how this relationship works in more detail.
As of Monday afternoon, there were more than 6.2 million infections and at least 373,883 deaths worldwide from coronavirus.