COVID-19 spreads easier in dry air

COVID-19 has been torturing the world for this entire year, but we are still learning about it and the ways it spreads. Researchers at the University of Sydney together with their colleagues in China have now found an association between lower humidity and an increase in community transmission.

The fact that COVID-19 spreads easier in dryer air is a good argument to wear masks. Image credit: via Wikimedia (CC BY 4.0)

These findings are not entirely new. The same team discovered this association back in the early stages of epidemic. However, in this new study scientists managed to prove that low humidity helps SARS-CoV-2 virus to spread easier. These findings have implications on how we are going to continue to deal with this COVID-19 pandemic in the coming months and years.

Low humidity, usually called just dry air, is estimated to be responsible for a 7-8 % increase in COVID-19 cases as relative humidity drops by 1 %. 10 % drop in relative humidity is associated with a 2-fold increase in COVID-19 notifications. Relative humidity, of course, is strongly related to seasons, supporting the assumption that COVID-19 is going to be more or less a seasonal problem. Humidity usually drops in winter, especially in colder climate countries. But why does humidity matter so much?

It is actually not that surprising, because relative humidity or dryness of air matters for the transmission of other airborne viruses as well. Professor Michael Ward, lead author of the study, explained: “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”. Interestingly, rainfall doesn’t seem to affect the spread of COVID-19, other than forcing people indoors.

This is another argument to wear a mask. They do help preventing infectious aerosols escaping into the air and reduce the probability of inhaling such aerosols. Scientists note that aerosols are smaller than droplets, but even simple cloth masks do seem to help at least a little bit. Also, as winter is nearing, you should understand that humidity decreases during colder periods of the year. In other words, prepare to strengthen your defences.

As usually, further research is needed. Scientists want to continue studying humidity and how it affects the spread of COVID-19. They want to do it for the remainder of the year to establish the connection between the seasonal humidity and the frequency of COVID-19 cases. This information will be very important in the future, but for now, please, wear a mask whenever you enter a public space.


Source: University of Sydney

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