28 Apr 2020

Where did the two metre coronavirus rule come from?

One of the few constants during the coronavirus pandemic has been the edict to stay two metres away from other people. But where did the rule come from, and what evidence is it based on?

A search through internet archives shows that the government issued guidance on the rule in relation to COVID-19 on 22 January, over a month before a pandemic was declared and the UK lockdown began.

But it’s also been the rule for other viruses and bacterial infections during epidemics, from swine flu in 2009 to SARS in 2002.

In fact, Professor Paul Hunter from the University of East Anglia told Channel 4 News that two metres has been part of the received wisdom on infection control since even further back than that.

“The evidence originally comes from studies around the spread of infection between people based on how far the beds were, and I think it dates back to World War II,” he said. “Generally if the beds were spaced more than about a metre apart, then there was lower risk of spread.”

By the time Professor Hunter was studying medicine, he said two metres was being taught as a generally accepted rule for lowering the risk of disease transmission.

But what’s actually happening, or not, when people are two metres apart?

“The first thing you’ve got to know is the distinction between droplet spread and airborne spread, which a lot of people get muddled up,” Professor Hunter said.

Droplet spread is when a virus is contained in large drops produced by coughing or sneezing, and tend to fall out the air quickly and not far from where they came.

Airborne spread is when much smaller particles called aerosols are produced which can potentially drift in the air much further.

The majority of the research on COVID-19 transmission suggests it isn’t airborne spread, however, but rather by droplets and any surfaces the droplets land on.

“The epidemiology is about the most common things, so you can’t say that it never spreads by aerosol,” Professor Hunter said. “But as long as you’re providing droplet spread protection, that’s the vast majority of cases prevented.”

Dr Ben Killingley from University College London Hospital told Channel 4 News that even if we were to discover later on that coronavirus can be spread by aerosols, it would only be a technical point.

That’s because it’s clear from the existing research that close contact is where the disease spreads, so aerosol transmission would still appear to require high concentrations at close range to infect.

None of this would change the existing public health advice, he said.

Both experts point out that distancing itself is no more important than other hygiene precautions, including proper handwashing and avoiding touching the face – especially when out in public.