The results, reported in the journal Proceedings of the Royal Society A, show that social distancing measures alone do not provide adequate protection from the virus, and further emphasise the vital importance of ventilation and face masks in order to slow the spread of COVID-19.
The researchers, from the University of Cambridge and Imperial College London, used mathematical models to show how SARS-CoV-2 – the virus which causes COVID-19 – spreads in different indoor spaces, depending on the size, occupancy, ventilation and whether masks are being worn. These models are also the basis of a free online tool, Airborne.cam, which helps users understand how ventilation and other measures affect the risk of indoor transmission, and how that risk changes over time.
The researchers found that when two people are in a poorly-ventilated space and neither is wearing a mask, prolonged talking is far more likely to spread the virus than a short cough. When speaking, we exhale smaller droplets, or aerosols, which spread easily around a room, and accumulate if ventilation is not adequate. In contrast, coughing expels more large droplets, which are more likely to settle on surfaces after they are emitted.
It only takes a matter of seconds for aerosols to spread over two metres when masks are not worn, implying that physical distancing in the absence of ventilation is not sufficient to provide safety for long exposure times. When masks of any kind are worn however, they slow the breath’s momentum and filter a portion of the exhaled droplets, in turn reducing the amount of virus in aerosols that can spread through the space.
The scientific consensus is that the vast majority of COVID-19 cases are spread through indoor transmission – whether via aerosols or droplets. And as was predicted in the summer and autumn, now that winter has arrived in the northern hemisphere and people are spending more time indoors, there has been a corresponding rise in the number of COVID-19 cases.
Image: Five senses series - Taste 1/2
Credit: Gauthier DELECROIX - 郭天
Reproduced courtesy of the University of Cambridge