Rigid Covid-19 social distancing measures are based on "outdated science" with experiences of past viruses, a report published in the <em>British Medical Journal</em> said. In <a href="https://www.bmj.com/content/370/bmj.m3223">the report,</a> scientists at the University of Oxford, Massachusetts Institute of Technology and London's St Thomas's Hospital said rules that ensure people stay one or two metres apart are based on viral transfer by large droplets or small airborne ones. But they do not account for the exhaled air that carry them. The World Health Organisation advises people to keep at least a one metre apart from others to ensure the coronavirus does not spread, up from an earlier two metres. But the report's authors say transmission is more complex. The origins of the two-metre rule date to the 19th century and early studies took it as the baseline for most airborne contagious diseases. But recent evidence indicates that small water droplets carrying the coronavirus can travel more than two metres by when released through coughing and shouting. They can spread up to eight metres concentrated in exhaled breath from an infected person. If the person is silent, however, the risk is much lower in most settings. <a href="https://www.nejm.org/doi/full/10.1056/nejmoa032867">Other recent studies</a> suggest that recent related viral outbreaks such as Sars, Mers and Avian flu can spread beyond two metres. The scientists suggest distancing rules need to take account of several factors that affect risk, including type of activity, whether settings are indoors or outdoors, ventilation levels and whether face masks are worn. The concentration of virus the emitter is carrying, how long they are exposed to the coronavirus and the susceptibility of a person to infection are also important factors. The authors propose graded safety recommendations based on those factors. “This would provide greater protection in the highest risk settings but also greater freedom in lower risk settings, potentially enabling a return towards normality in some aspects of social and economic life,” they said. Transmission risk will vary depending on settings. In the highest risk situations, such as a crowded bar or nightclub, physical distancing beyond two metres and minimising the times people are allowed to stay should be considered. Less stringent distancing is likely to be enough in low-risk scenarios, such as sparsely populated outdoor spaces. “Physical distancing should be seen as only one part of a wider public health approach to contain the Covid-19 pandemic,” the authors say. “It should be used in combination with other strategies to reduce transmission risk, including hand washing, regular surface cleaning, protective equipment and face coverings where appropriate, strategies of air hygiene and isolation of affected individuals.” Earlier on Tuesday, Prof John Bell, part of a team of University of Oxford researchers working on a promising potential vaccine for the coronavirus, said he was optimistic that data proving its effectiveness would be available to regulators as early as this autumn.