Alex Pantling/Getty Images
For three months, Britons have been advised to keep a wide berth from other people: two metres, to be precise. The two metre rule has been sprayed on pavements, emblazoned at park entrances and drilled into people at daily press conferences. But with the government reportedly weighing up to whether to scrap the two metre rule, its days could be numbered.
The UK’s insistence on two metres already makes it something of an outlier. Germany, Italy and Austria all went for a 1.5 metre rule, while the more imperially-minded United States went for a six feet (1.8 metre) buffer. The World Health Organisation (WHO) recommends a minimum distance of one metre, a recommendation followed by Denmark, France, China and Singapore.
The pressure to reduce the distance rule is coming from shops and restaurants, which have warned that the two metre distance could make it impossible to do business, and the chancellor Rishi Sunak has already indicated that the government is reviewing the measure. So how does a two metre rule stack up against the other options when it comes to reducing the risk of people passing on coronavirus?
The social distancing standards can be traced back to research in the 1930s, when William F. Wells studied infectious diseases like tuberculosis at Harvard University. His experiments showed that most droplets sprayed from the mouth tend to fall to the ground after between one and two metres. Research into the influenza virus, which also spreads via droplets from the nose or mouth, has yielded similar results: One study from 2013 suggested that when healthcare workers were within 1.8 metres of patients with the flu, their risk of becoming infected was higher. Because this sort of research still had to be done when the novel coronavirus first emerged, the WHO recommended keeping a distance of at least one metre to reduce the risk of transmission.
Most of the studies that investigate how exactly the coronavirus spreads is carried out in laboratories or in healthcare settings and doesn’t easily translate into real-life situations. Researchers from McMaster University in Ontario analysed data from previously published studies to estimate the risk of infection at different distances. Their review, which was commissioned by the World Health Organisation and published on June 1 in The Lancet, considered also how face masks and eye protection might help prevent coronavirus transmission through person-to-person contact.
The team found that the most important factor was staying more than one metre away from other people. Within one metre, the risk of being infected was about 13 per cent but beyond that the risk dropped to three per cent, with the risk halved by each extra metre up to three metres. Because the researchers compared studies carried out in different settings and that didn’t take account of the duration of exposure, the review has been met with criticism – most of which the researchers acknowledge in their report.
“The research in this area is not very good. We tried to draw conclusions on the basis of how studies reported distances, how they reported whether or not there was face-to-face or any physical contact,” says lead author Holger Schünemann, an epidemiologist and physician at McMaster University. People aren’t very good at accurately estimating distance when recalling their encounters, which also leaves room for error. How long a person is exposed to the virus is important, too; while keeping two metres from a person may be safer, the risk increases the longer a face-to-face interaction goes on for.
Randomised control trials would be the gold standard for studying the effects of social distancing on the risk of infection, but they would be virtually impossible in practice. “Ideally, we would have randomised controlled experiments for these types of questions, but we don’t and we will not for distance measures unless you start randomising cities, counties or jurisdictions,” says Schünemann. If an experiment focused on just London, for instance, researchers would need to randomly allocate different distances to study participants that then go about their day in places where they are likely exposed to crowds, contaminated surfaces or other risk factors. Some study participants would simply not adhere to the instructions.
Virus-laden saliva or mucus may not be the only route of transmission. Emerging evidence suggests tiny particles of coronavirus can drift in the air. “The big unknown question that has not been answered in the literature as far as I can see is the extent to which it is airborne. So to what extent can the virus transfer in tiny, tiny aerosol droplets that are basically just suspended in the air. They’re there for a little while and if you walk through them, you come into contact with them,” says Linda Bauld, professor of public health at the University of Edinburgh. Most of the existing studies on physical distancing are based on people coughing, sneezing or breathing.
In the laboratory, researchers are investigating how the virus floats through the air. One experiment described how it lingered for up to three hours in the air while computer simulations run by Dimitris Drikakis and Talib Dbouk from the University of Nicosia in Cyprus showed that at wind speeds of four to 15 km/h, saliva droplets could travel up to six metres. “We found that the droplets dispersion in the air is important and can occur at long distances and at different rates depending on the environment. Our findings imply that depending on the environmental conditions, two meters social distancing may not suffice,” says engineering professor Drikakis. He adds that shorter adults and children could be at higher risk if they are within the trajectory of the travelling aerosols.
The little evidence that is available shows that physical distance does matter when it comes to breaking the chains of person-to-person transmissions. But so do other measures. Whether the UK reduces its physical distancing rule from two metres to 1.5 metres or not, the hospitality businesses will need to “virus-proof” their spaces – from proper ventilation to one-way systems to frequent hygiene. Ultimately, Bauld says, the UK will need to establish a robust test and trace system to guide the economy safely out of lockdown. “Most European countries are well ahead of us and they have 1.5 or 1-metre [rules]. They’ve not seen big rises in cases,” says Bauld. “You need to know where your cases are. The test, trace and isolate is basically how all the countries that have done this well have dealt with it,” she says.
More great stories from WIRED
🦆 Google got rich from your data. DuckDuckGo is fighting back
💰 The Animal Crossing fans running in-game businesses
🤑 Inside the ‘bullshit’ get-rich-quick world of dropshipping
🎵 The secret behind the success of Apple’s AirPods
🔒 The UK’s lockdown rules, explained
👉 Follow WIRED on Twitter, Instagram, Facebook and LinkedIn
Get The Email from WIRED, your no-nonsense briefing on all the biggest stories in technology, business and science. In your inbox every weekday at 12pm sharp.
Thank You. You have successfully subscribed to our newsletter. You will hear from us shortly.
Sorry, you have entered an invalid email. Please refresh and try again.