With the Covid alert level being reduced from 4 to 3 it is surely only a matter of days before the government announces that it is relaxing the two metre rule – a move for which the hospitality industry has been lobbying for heavily, warning that pubs and restaurants will not be able to reopen until it happens. Another sign of impending change came from Professor Calum Semple of the University of Liverpool, a member of the Sage committee, who told the Today programme this morning that he had changed his mind on the two metre rule and now believes that infection levels are low enough to make it safe.
But was there ever any scientific justification for the two metre rule? It is based on the presumption that Covid-19 is most likely spread via the heavier droplets emitted from the mouth and nose, and which are most likely to fall out of the air within two metres. But as for hard evidence of transmission in this form? There isn’t any, according to Carl Heneghan and Tom Jefferson of the Oxford Centre for Evidence-Based Medicine. For the past few days they have been involved in a tussle with the Lancet over a World Health Organisation-funded evidence review published in the journal. The review looked at 172 studies from 16 countries and concluded that transmission of the virus is lower where there was physical distancing of one metre or more.
Except, claim Heneghan and Jefferson, the studies do not show this at all. Many, they say, are retrospective studies or show biases which undermine their claims. Only five of the studies, they claim, specifically reported distances between infected people – and these studies involved a mere 477 people and 26 cases of infection. Heneghan and Jefferson looked more closely at 15 of the studies and say that they were unable to reproduce the results in 13 of them. In several cases, they assert, there was no good evidence of the distance people in these studies were from the people they are deemed to have caught the disease from – it was just inferred that people were a certain distance away from each other. In one case – a Boeing 737 on which some passengers fell ill and some did now – there was a discrepancy as to whether rows of seats are 1.5 metres or two metres apart.
The Lancet has rejected Heneghan and Jefferson’s criticisms. Even so, it is clear there is no definitive evidence as to how the SARS-CoV-2 virus is actually spread, and therefore no way of justifying social distancing of one metre, two metres or whatever. We still do not know whether the virus is spread more by air droplets, large or small, or via touching surfaces. In spite of vast numbers of scientists working on the virus, the government is still groping in the dark – although hopefully with gloves on.