The 2-metre rule, introduced to help protect people from spreading COVID-19, may be less effective than originally supposed

Man coughing

The 2-metre rule, introduced to help protect people from contracting severe acure respiratory syndrome coronavirus 2 (SARS-CoV-2), may be less effective than originally supposed, scientists have said.

The advice was issued by the Government soon after the COVID-19 pandemic took hold, although later eased to as little as 1 metre—subject to mitigations to reduce risk—to help the economy recover.

However, engineers at the University of Cambridge have found that the 2-metre rule does not represent a concrete measurement of safety, but was instead chosen from a risk ‘continuum’. They said that a ‘safe’ distance could have been set to anywhere between 1 and 3 or more metres.

First author Shrey Trivedi from the University of Cambridge Department of Engineering, who led the research, said: ‘One part of the way that this disease spreads is virology: how much virus you have in your body, how many viral particles you expel when you speak or cough.

‘But another part of it is fluid mechanics: what happens to the droplets once they’re expelled.’

Airborne transmission

The study, based on computer modelling and published in the journal Physics of Fluids, found that when an infected person without a mask coughs, most of the larger droplets fall on nearby surfaces.

However, the scientists found that smaller droplets from an infected individual without a mask can spread well beyond 2 metres, even when outdoors.

An additional factor behind infection risk was found to be the strength of cough and surrounding air conditions.

‘Each time we cough, we may emit a different amount of liquid, so if a person is infected with COVID-19, they could be emitting lots of virus particles or very few, and because of the turbulence, they spread differently for every cough’, explained Trivedi.

Environmental conditions

According to Professor Epaminondas Mastorakos, also from the Department of Engineering: ‘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 2-metre mark can be very different each time.’

Mitigating risk by vaccination, ventilation, and mask wearing are vital to stopping the SARS-CoV-2 virus from spreading, the authors concluded. However, they acknowledged that the 2-metre rule has been a memorable message for the public.

‘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’, said Professor Mastorakos.

With the onset of colder weather, the team are continuing their research with similar simulations for spaces such as lecture rooms, to help assess the risks faced by people who spend more time indoors.

This article originally appeared on Medscape, part of the Medscape Professional Network.

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