Reducing physical distancing advice from 2 metres to 1 metre could double the risk of coronavirus infection, according to the most comprehensive study to date.
The research, part-funded by the World Health Organization (WHO) and published in the Lancet, will add to the debate in the UK about whether the 2-metre rule should be reduced.
Last week, Boris Johnson said he hoped to “be able to reduce that [2-metre] distance”, to make it easier to travel on public transport and boost the hospitality industry. This would allow extra people inside workplaces, restaurants, pubs and shops, and reduce the length of queues. The prime minister has instructed the Scientific Advisory Group for Emergencies (Sage) to look into the possibility.
The UK guidance is out of line with advice in most other countries and with recommendations from the WHO, which says people should stay 1 metre apart. This is followed by France, while countries such as Germany and Australia have a 1.5-metre rule.
The Lancet’s meta-analysis of observational studies across Covid-19 but also – predominately – Sars and Mers, highlights the potential consequences of a change.
It found that keeping a distance of more than 1 metre from other people reduced the risk of infection to 3%, compared with 13% if standing within a metre. However, the modelling also suggested that for every extra metre further away up to 3 metres, the risk of infection or transmission may halve.
Linda Bauld, professor of public health at the University of Edinburgh, who was not involved in the research, said: “The most useful finding is that physical distancing matters. There have been plenty of complaints that the guidance in the UK on 2 metres distance is excessive because it is more than in other countries. But this review supports it.
“Maintaining this distance is likely to reduce risk compared to 1 metre. Thus, where possible, this is the distance that retailers and employers should use as more premises and workplaces reopen in the future. This is going to be very difficult in some settings but is important and we’ll all need to get used to maintaining this distance for some months to come.”
The World Health Organization (WHO) guidance on face masks has remained consistent during the coronavirus pandemic. It has stuck to the line that masks are for healthcare workers – not the public.
“Wearing a medical mask is one of the prevention measures that can limit the spread of certain respiratory viral diseases, including Covid-19. However, the use of a mask alone is insufficient to provide an adequate level of protection, and other measures should also be adopted,” the WHO has stated.
Nevertheless, as some countries have eased lockdown conditions, they have been making it mandatory to wear face coverings outside, as a way of trying to inhibit spread of the virus. This is in the belief that the face covering will prevent people who cough and sneeze ejecting the virus any great distance.
There is no robust scientific evidence – in the form of trials – that ordinary masks block the virus from infecting people who wear them. There is also concerns the public will not understand how to use a mask properly, and may get infected if they come into contact with the virus when they take it off and then touch their faces.
Also underlying the WHO’s concerns is the shortage of high-quality protective masks for frontline healthcare workers.
Nevertheless, masks do have a role when used by people who are already infected. It is accepted that they can block transmission to other people. Given that many people with Covid-19 do not show any symptoms for the first days after they are infected, masks clearly have a potential role to play, especially on crowded public transport as people return to work.
Sarah Boseley Health editor
The researchers also wade into the debate about face masks. Based on evidence from 10 studies involving 2,647 participants, they found that the risk of infection or transmission when wearing a mask was 3% compared with 17% when not wearing a mask, although they said the level of certainty was “low”. Similar benefits were found, also with low certainty, concerning wearing of protective eye coverings such as face shields, goggles and glasses.
Respirator-type masks were found to offer more protection from viral transmission to healthcare workers than surgical masks. The authors also found that multi-layer masks were more effective than single-layer ones, which may help guide people making their own face coverings at home.
Business leaders have warned that if the 2 metre distance is not reduced it could make their companies unsustainable, despite the relaxation of lockdown. Greg Clark, the chairman of the Commons science and technology select committee, told the Telegraph he had written to Johnson urging him to urgently review whether it was possible to reduce the distance to 1.5 metres.
“The difference between 2 metres and 1.5 metres may seem small but it can be the difference between people being able to go to work and losing their jobs,” Clark said.
Last month, Yvonne Doyle, the medical director of Public Health England (PHE), told the committee PHE was looking at “whether 2 metres is actually necessary or could it be reduced further”.
The distance is based on the belief that when people cough and sneeze large respiratory droplets, believed to be the main means of transmission of Covid-19 along with contact, they will travel no more than 2 metres before falling to the ground. However, some believe this to be an underestimate. Additionally, debate remains about whether smaller aerosols can cause transmission.
The authors of the Lancet paper analysed nine studies involving 7,782 participants relating to physical distancing across the three viruses, reaching conclusions with “moderate certainty”.
Prof Holger Schünemann from McMaster University in Canada, who co-led the research, told the Guardian: “We have a suggestion here that 2 metres might be more effective than 1 metre distance. And what that would mean is if one were to implement a policy, and particularly if 2 metres were already in place, 2 metres may be the right policy to undertake.”
How countries’ rules differ
UK: Physical distance requirement of 2 metres; guidance says a face covering should be worn in “enclosed spaces” where physical distancing may be difficult, such as on public transport or in some shops.
Germany: Physical distance requirement of 1.5 metres; face masks compulsory on public transport and shops (although some variation by state).
Australia: Physical distance requirement of 1.5 metres; face masks not required.
France: Physical distance requirement of 1.5 metres; face masks compulsory on public transport and in secondary schools, and shops can require customers to wear them.
Vietnam: Physical distance requirement of 1 metre; face masks compulsory in public.
Sweden: Neither physical distancing nor face masks prescribed, with the Swedish health ministry stipulating that the latter are “not needed in everyday life”.