Research links COVID-19 and lower humidity

If COVID-19 is a seasonal illness, is our easing of restrictions going into winter a good idea?

In winter, humidity is likely to drop and that’s not good news for avoiding COVID-19.

New Australian research by the University of Sydney indicates that a 1 per cent decrease in humidity can increase the number of COVID-19 cases by 6 per cent.

That was the probability suggested by a new Australian study published in Transboundary and Emerging Diseases, which found an association between lower humidity and an increase in positive cases of COVID-19.

The pandemic in China, Europe and North America happened in winter and humidity during that period was the most important factor that explained when the cases were occurring.

When there is low humidity, there’s not much water vapor in the air. The air is very dry and that means when someone coughs, particularly an infectious person, you get aerosolised particles in the air.

When the air is dry, those particles are small, so they can stay suspended for much longer in the air.

When it’s humid and there’s a lot of water in the air, those particles are quite big and they’re heavy, and they drop fairly quickly. That reduces the potential exposure to other people and transmission.

The theory appears to ring true for the Northern Territory, where to date just 29 cases have been recorded and zero deaths. Similarly in Cairns and Townsville in North Queensland there were a combined total of 58 cases and no fatalities.

But researchers caution it is hard to say for certain whether the low numbers are due to climate or public health efforts such as social distancing measures and the closure of borders.

The research indicates that heading into Winter people living in Australia’s southern coastal areas will be at the highest risk.

While Australia’s case numbers remain relatively low, helping to pave the way for the easing of social distancing measures heading into winter, the research highlights the need to be vigilant.

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