In a new study, researchers found rules which stipulate a single specific physical distance (1 or 2 meters) between individuals to reduce the spread of COVID-19 are based on outdated science and experiences of past viruses.
Such rules are based on an over-simplistic dichotomy describing viral transfer by either large droplets or small airborne droplets emitted in isolation without accounting for the exhaled air.
In reality, the transmission is more complex, involving a continuum of droplet sizes and an important role of the exhaled air that carries them, they explain.
The research was conducted by a team at the University of Oxford.
Evidence suggests that smaller airborne droplets laden with COVID-19 can travel more than 2 meters by activities such as coughing and shouting and may spread up to 7-8 meters concentrated in exhaled air from an infected person.
As such, the researchers say distancing rules need to take account of the multiple factors that affect risk, including the type of activity, indoor versus outdoor settings, level of ventilation, and whether face coverings are worn.
Viral load of the emitter, 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.
To facilitate this, they discuss how transmission risk may vary with setting, occupancy level, contact time, and whether face coverings are worn.
For example, in the highest risk situations, such as a crowded bar or nightclub, physical distancing beyond 2 meters and minimizing occupancy time should be considered, while less stringent distancing is likely to be adequate in low-risk scenarios.
They 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.
One author of the study is Nicholas Jones.
The study is published in BMJ.
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