COVID-19: Australian Researchers Say Reduced Humidity Linked To Increased COVID-19 Risk, Cooler Months To Be Worse
: Researchers from University Of Sydney have found an association between lower humidity and an increase in locally acquired positive cases. It was discovered that a 1 percent decrease in humidity could increase the number of COVID-19 cases by 6 percent.
The new research led by Professor Dr 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.
The research findings were published in the journal: Transboundary and Emerging Diseases
Dr Ward added, "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."
However additional studies including during winter in the southern hemisphere are needed to determine how this relationship works and the extent to which it drives COVID-19 case notification rates.
Past research has identified a link between climate and occurrence of SARS-CoV cases in Hong Kong and China, and MERS-CoV cases in Saudi Arabia, and a recent study on the COVID-19 outbreak in China found an association between transmission and daily temperature and relative humidity.
Dr Ward further added, "The pandemic in China, Europe and North America happened in winter so we were interested to see if the association between COVID-19 cases and climate was different in Australia in late summer and early autumn. When it comes to climate, we found that lower humidity is the main driver here, rather than colder temperatures. 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."
Dr Ward said there are biological reasons why humidity matters in transmission of airborne viruses.
He elaborated, "When the humidity is lower, the air is drier and it makes the aerosols smaller. 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."
The research team studied 749 locally acquired cases of COVID-19 mostly in the Greater Sydney area of the state of New South Wales between February 26 and March 31. The team matched the patients' postcodes with the nearest weather observation station and studied the rainfall, temperature and humidity for the period January to March 2020.
The research found lower humidity was associated with an increased case notifications; a reduction in relative humidity of 1 percent was predicted to be associated with an increase of COVID-19 cases by 6 percent.
Dr Ward said, "This means we need to be careful coming into a dry winter and noting that the average humidity in Sydney is lowest in August.”
He warned that even though the cases of COVID-19 have gone down in Australia, people still need to be vigilant and public health systems need to be aware of potentially increased risk when the region is under a period of low humidity. Ongoing testing and surveillance remain critical as Australia enters the winter months, when conditions may favor coronavirus spread.
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