One metre or two? When it comes to social distancing, researchers in the British Medical Journal now argue that the concept of a single number is based on outdated science.
They believe rules stipulating such specific distances between individuals to reduce the chance of spreading Covid-19 are based on experiences of past viruses.
Nicholas Jones, at the University of Oxford's Department of Primary Care Health Sciences, together with his colleagues, says these restrictions rely on an "over-simplistic dichotomy" looking at viral transfer by either large droplets or small airborne droplets emitted in isolation.
In reality, they argue, transmission is more complex and involves the important role of exhaled air that carries these droplets.
As such, their opinion piece sets out that distancing rules must take account of multiple factors – the type of activity, indoor versus outdoor settings, the level of ventilation and the presence of face coverings.
“Physical distancing should be seen as only one part of a wider public health approach to containing the Covid-19 pandemic,” they conclude.
“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.”
Viral load
Evidence suggests that smaller airborne droplets laden with Covid-19 can travel more than two metres through coughing and shouting, among other actions. They may even spread up to eight metres, concentrated in exhaled air from an infected person.
The authors also believe when considering such questions, that the viral load of the person spreading it, the duration of exposure, and the susceptibility of an individual to infection are also important.
“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 write.
In discussing how transmission risk might vary depending on the setting and other considerations, they look at high risk situations such as a crowded bar or nightclub. Here, physical distancing beyond two metres and minimising occupancy time should be considered, while less stringent distancing is likely to be adequate in lower-risk scenarios.
They say further work is needed to examine areas of uncertainty and extend the guide to develop specific solutions to different indoor environments with varying occupancy.
