Two metres better than one, says review

08 June 2020

Interview with 

Holger Schünemann, McMaster University

2_METRES

Sign indicating people should keep 2 metres apart.

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The UK government’s coronavirus advice is still to keep 2 metres apart - but the World Health Organisation has been recommending 1 metre. Well new research, funded by the WHO itself suggests: yes, two metres is better. It may even be twice as effective at stopping the virus spreading as one metre - although these are transmission rates of 2.6% compared to 1.3%, so not huge in absolute terms. These results are from an in-depth review of the science published on the subject so far - which Phil Sansom heard about from lead researcher Holger Schünemann…

Holger - We found that physical distancing, the use of facemasks, and eye protection reduce the risk of SARS-Cov-2 virus transmission and infection.

Phil - Really? So all these things that we've been told to do - they do actually seem to work?

Holger - Yes. Up until now we had individual studies looking at many of these issues and that often leads to somewhat variable results and interpretations. What we did was we looked at all of the available evidence, and summarised and synthesised them using sophisticated techniques that we call meta-analysis.

Phil - So you're going through past research on all of these things?

Holger - That's right. There is always a degree of random error in every single piece of research, and these types of techniques that we utilised try to reduce both random error, as well as potential bias in research or systematic error. We found 170 studies that fulfilled our inclusion criteria. They were done in 16 countries, in six continents. After going through all of these studies, we found 44 studies that allowed us to make comparisons that we were actually interested in.

Phil - And just to clarify, are these people who have studied how well these things work for this coronavirus, for COVID-19?

Holger - We included studies that looked at COVID-19, but also studies that included SARS - which was an epidemic that took place in the early 2000s - and MERS. These three diseases are caused by very similar viruses. For the question about distancing, we found moderate-certainty evidence; we found low-certainty evidence for the use of masks; and we found low-certainty evidence for the use of eye protection. Now this is all due to the fact that the studies that we identified were what we called observational in nature, as opposed to randomised control trials.

Phil - What about - did you find that keeping one metre apart from other people made a big difference compared to, for example, keeping two metres apart from other people?

Holger - Yeah. What we found was that keeping two metres apart might be more protective than keeping one metre apart. It seems to provide a twofold increase in protection.

Phil - Wow. So a lot of people right now are asking... hoping that these restrictions are going to get eased a little bit, we'll go down to one metre. It seems that you've found that's actually maybe not a great idea.

Holger - We are not providing guidance or recommendations. Many factors will influence whether or not a policy of one metre should be implemented, one and a half metres, or two metres. One thing that we could say is that if you have a policy of two metres and it is accepted, that might provide greater protection than one metre.

Phil - And does it make a difference whether you're inside or outside?

Holger - Difficult to answer for the time being. Outside, obviously there are lots of other factors that influence whether or not the virus potentially might spread; for instance, wind, the number of people that you're exposed to. Inside typically exposure is for a longer period of time, possibly. So this data doesn't necessarily allow us to solve that puzzle.

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