RULES WHICH SPECIFY a single physical distance (one or two metres) between individuals to reduce the spread of Covid-19 are based on outdated science and experiences of past viruses, researches have argued in the BMJ journal. 

Such rules are based on an over-simplistic dichotomy describing viral transfer by either large droplets or small airborne droplets released in isolation without accounting for the exhaled air, Nicholas Jones at the University of Oxford and colleagues have claimed.

In reality, transmission is more complex, involving a continuance of droplet sizes and an important role of the exhaled air that carries them, they explain.

The researchers say evidence suggests that smaller airborne droplets containing Covid-19 can travel more than two metres by activities such as coughing and shouting, and may spread up to seven to eight metres concentrated in exhaled air from an infected person.

As a result, they say social distancing rules need to take account of the multiple factors that affect risk, including type of activity, indoor versus outdoor settings, level of ventilation, and whether face coverings are worn. 

The viral load of the person infected, duration of exposure, and susceptibility of an individual to infection are also important, they add. 

“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. 

The researchers discuss how transmission risk may vary with setting, occupancy level, contact time, and whether face coverings are worn. 

They say, for example, in the highest risk situations, such as a crowded bar or nightclub, physical distancing beyond two metres and minimising occupancy time should be considered, while less stringent distancing is likely to be adequate in low risk scenarios.

The researchers say further work is needed to examine areas of uncertainty and extend the guide to develop specific solutions to classes of indoor environments occupied at various usage levels.

“Physical distancing should be seen as only one part of a wider public health approach to containing the Covid-19 pandemic,” the researchers 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.”

At present, people in Ireland are being asked to keep a space of two metres between themselves and others outside of their household. 

When it is difficult to keep two metres from others in public places, people are asked to wear a face covering.