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Masks can block 99.9% of COVID-linked droplets


Paul Hayes


5/01/2021 2:32:53 PM

With face masks now mandatory in multiple settings, research shows they are ‘highly effective’ at reducing spread of respiratory droplets.

Illustration of people wearing masks
‘Wearing a face covering will reduce the probability that someone unknowingly infected with the virus will pass it on,’ one researcher said.

Opinions on wearing a face mask to help stop the spread of coronavirus, to put it mildly, vary across a wide spectrum.
 
‘The least we can do.’
 
‘I have no issue wearing a mandated face mask.’
 
‘There’s limited data on whether face masks are actually effective.’
 
‘I would rather be a human than a slave.’
 
With face masks now mandatory in multiple settings in NSW and Victoria, proof they work in helping to stop the spread is vital.
 
Fortunately, new research has confirmed their efficacy, finding face masks reduce the risk of spreading large COVID-linked droplets when speaking or coughing by up to 99.9%.
 
‘As these droplets are likely to be the main driver of SARS-CoV-2 transmission, our data suggest that the wearing of masks can substantially reduce the probability of an infected person transmitting the virus,’ the researchers wrote.
 
The study, recently published in Royal Society Open Science, measured droplets spread by people coughing and speaking with and without surgical or handmade cotton face masks.
 
Researchers estimate a person standing 2 m from someone coughing without a mask is exposed to more than 10,000 times more respiratory droplets than from someone standing 0.5 m away wearing a basic single-layer mask.
 
The impact on aerosol transmission was not tested.
 
‘The simple message from our research is that face masks work,’ researcher Professor Paul Digard said. ‘Wearing a face covering will reduce the probability that someone unknowingly infected with the virus will pass it on.’
 
The researchers conducted experiments using a manikin and then real people to simulate droplet trajectory from coughing and talking.
 
‘These experiments demonstrate that both surgical and simple handmade masks such as a single-layer cotton mask can suppress the risk of direct person-to-person virus transmission through large droplet deposition,’ they wrote.
 
‘Assuming that SARS-CoV-2 virus transmission through aerosol is small compared to through large droplets, these results suggest that physical distancing can be reduced with the use of face coverings.’
 
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Dr Michael Smith   6/01/2021 1:02:33 AM

I think the article that is proffered as proof of mask efficacy assumes too much and therefore the conclusions are not reliable. It only shows that face coverings reduce droplet deposition in a very controlled setting. The authors admit to their contrivance: "Air was ejected at velocities and flow rates within the range of those observed from real individuals [19,20] but droplets were ejected at a higher volume rate. Hence, the physical interaction between the droplets and the airflow jet [21,24] was not correctly represented'. The data is certainly not reliable enough to inform public policy. The assumption that droplets are the primary agent of COVID transmission is tempered by the findings of aersol transmission. Simple masks intrain air from several ankles more than just front on droplets. I am afraid I am not convinced by this article.


Dr Ailsa Mary Carole Laidlaw   6/01/2021 8:45:41 AM

Their data graphs show almost zero droplets with or without a mask for any distance beyond 400mm with speaking. I don't know many people who would be comfortable 40cm from another person's face. The conclusions are not supported by their data .....for speaking.
The data for coughing is different.....it does show mask benefit up to 2 m. But this is for coughs directed at the other person. Cough etiquette was not tested.
It may be much more effective to promote cough etiquette than dictate masks in all indoor settings. (There are exceptions where close , prolonged contact is unavoidable, such as public transport).