Social distancing is still required for those with persistent coughs as face masks are not enough in themselves to protect other people, new research has found.
Masks are more efficient than no mask at all, but droplets from people with coughs can travel up to one metre even with a mask, according to researchers at the University of Nicosia in Cyprus.
The debate over face masks has intensified in recent weeks with the National Public Health Emergency Team (NPHET) recommending that people wear them in public, though the Government is not planning to make them compulsory on public transport like others countries have done.
The chief medical officer Dr Tony Holohan has said there is increasing evidence that was not there at the start of the pandemic that face coverings work.
“It is our clear recommendation that people in those settings should wear [face coverings] and maybe the shops and retail environments might take steps to remind the public of the importance of the advice we’re giving. I think we can do better,” he said on Friday.
According to researchers Talib Dbouk and Dimitris Drikakis, face masks are inefficient in protecting other people if the wearer has a bad cough.
Even when a mask is worn, some droplets can travel a considerable distance, up to a metre, during periods of mild coughing.
Without a mask, droplets travel twice as far, however, so wearing a mask will help. A mask also decreases the number of droplets that leak out the side of the mask but fails to eliminate it entirely.
The model was created using complex mathematical equations for turbulence and other flow effects.
The researchers performed numerical simulations that account for droplet interactions with the porous filter in a surgical mask.
“The droplet sizes change and fluctuate continuously during cough cycles as a result of several interactions with the mask and face,” said Mr Drikakis.
Mr Dbouk explained how droplet sizes might change. “Masks decrease the droplet accumulation during repeated cough cycles. However, it remains unclear whether large droplets or small ones are more infectious.”
Previous work from this research group showed droplets of saliva can travel five metres in five seconds when an unmasked person coughs.
This new work used an extended model to consider the effect of face masks and multiple cycles of coughing.
The results show masks can reduce airborne droplet transmission. However, the filtering efficiency of masks is adversely affected by repeated coughing, as might happen when an individual is ill. Repeated coughs reduce the efficiency, letting many more droplets through.
Mr Drikakis concluded that social distancing is still “essential” as a mask does not provide complete protection.
For health care workers, the investigators recommend much more complete personal protective equipment, including helmets with built-in air filters, face shields, disposable gowns and double sets of gloves.
The research is published in Physics of Fluids, a monthly journal established by the American Institute of Physics in 1958, and published by AIP Publishing.
