The two metre social distancing rule was “arbitrary” and is no guarantee of protection from COVID infection, according to a new analysis.
Scientists studying the transmission of COVID-19 via airborne droplets found that risk varies widely. They conclude that masks are much more effective protection than social distancing.
Writing in Physics of Fluids yesterday, Professor Epaminondas Mastorakos, of the University of Cambridge, UK, and his team state: "The ongoing pandemic caused by SARS-CoV-2 has reinforced the need to understand better the fluid mechanics controlling the spread of airborne diseases."
They looked at the position and size of evaporating droplets after a cough using simulation devices and computer modelling. The method demonstrated "large variations in the spatial distribution of the droplets".
This represents significant variations in the virus content potentially inhaled by a person nearby. The high variability "is due to the local fluctuations of temperature, humidity and velocity on droplet evaporation and motion," they explain.
"The droplet distribution suggests that, in the absence of face coverings, an unprotected cough is not safe at two metres away from the emitter, even outdoors."
Professor Mastorakos said: “I remember hearing lots about how COVID-19 was spreading via door handles in early 2020, and I thought to myself if that were the case, then the virus must leave an infected person and land on the surface or disperse in the air through fluid mechanical processes.”
He added: “Even if I expel the same number of droplets every time I cough, because the flow is turbulent, there are fluctuations. If I’m coughing, fluctuations in velocity, temperature and humidity mean that the amount someone gets at the two-metre mark can be very different each time.
“We’re all desperate to see the back of this pandemic, but we strongly recommend that people keep wearing masks in indoor spaces such as offices, classrooms and shops – there’s no good reason to expose yourself to this risk as long as the virus is with us,” he concluded.
Trivedi, S. et al. Estimates of the stochasticity of droplet dispersion by a cough. Physics of Fluids 23 November 2021; doi: 10.1063/5.0070528
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