Coronavirus: Will face masks reduce transmission?
The WHO advises a three-layer face covering: the outer layer should be water resistant, the inner water absorbent and the mid-layer acts as a filter.
It will soon be mandatory to wear a face covering in supermarkets and other shops in England.
Starting on 24 July, those going shopping need to have their nose and mouth covered or risk a £100 fine.
This comes after rules requiring people to wear face coverings on public transport became mandatory last month.
Initially many experts and authorities, including the World Health Organisation (WHO), suggested face coverings were not effective in preventing the spread of coronavirus but are now recommending wearing them in indoor spaces.
What does the science say?
A report recently published by the Royal Society, which has not yet been peer-reviewed, suggests that even basic homemade face coverings can reduce transmission if enough people wear them when in public.
The study, based on mathematical modelling, showed that if an entire population wore face coverings that were only 75 per cent effective, it would bring the R value, which is the number of people an infected individual passes the virus on to, from 4.0 to under 1.0, without the need for lockdowns.
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Meanwhile, another study which looked at coronavirus deaths across 198 countries found that nations which had policies favouring mask-wearing had lower death rates.
In another piece of scientific research, published in the journal Proceedings of the National Academy of Sciences last month, scientists calculated that wearing face coverings prevented more than 78,000 infections in Italy between 6 April and 9 May, and more than 66,000 infections in New York City between 17 April and 9 May.
Dr Julian Tang, who is a consultant virologist at the Leicester Royal Infirmary and honorary associate professor in the Department of Respiratory Sciences, said wearing face coverings in public places could keep the R value below 1.
It is the asymptomatic or the pre-symptomatic people where the mask has most benefit at the public health level
Dr Tang said: “If you look at other countries outside of the UK – such as Japan or Hong Kong – they have much higher masking percentages and are way below the epidemic curves of the West.”
But Dr Simon Clarke, an associate professor of cellular microbiology at the University of Reading, said that while face coverings may reduce the spread of cough droplets, robust epidemiological evidence on their benefits is still lacking.
He told the PA news agency: “You can see that [face coverings] are mechanistically obvious, but that is not borne out by what actually happens.
“What is really important is that you have the right mask, fitted properly and changed regularly.”
What are the benefits to wearing face masks?
Experts say the risk of coronavirus transmission appears to be higher in poorly ventilated indoor spaces and wearing face coverings in small shops or enclosed shopping centres could help reduce the spread.
Keith Neal, emeritus professor of the epidemiology of infectious diseases at the University of Nottingham, said: “Lack of strong evidence of their effectiveness should not be considered a problem but the evidence is accumulating that they have a part to play in reducing transmission and also in protecting the wearer.”
In addition, there is also increased evidence which suggests that many people with the virus who do not have symptoms can still be contagious.
Prof Neal told PA that while the evidence of the upsides of wearing face coverings is “supportive rather than definitive”, he adds that “it is the asymptomatic or the pre-symptomatic people where the mask has most benefit at the public health level”.
Meanwhile a report, published last month by the University of Oxford’s Leverhulme Centre for Demographic Science, noted: “Next to hand washing and social distancing, face masks and coverings are one of the most widely adopted non-pharmaceutical interventions for reducing the transmission of respiratory infections.”
What does this mean for office workers?
Experts say wearing face coverings could provide an added line of defence amid growing evidence of airborne transmission of coronavirus.
Airborne transmission involves tiny virus-containing droplets, less than five microns in diameter, suspended in the air (aerosols) that linger for some time.
Dr Tang said: “In the office, it may not be possible to maintain social distancing, you can’t always open the windows and ventilation is probably very nominal. So wearing a mask gives an extra layer of protection.
What are the downsides to wearing face coverings?
There are many indoor spaces, such as pubs and restaurants, where the use of face coverings may not be possible.
Dr David Strain, clinical senior lecturer at the University of Exeter, said: “In these locations, strict physical distancing of more than two metres and/or physical barriers should be used in order to protect the staff and other customers from the risk of asymptomatic carriers.”
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He added that for those who will be disadvantaged by a mandate to wear face coverings, such as those who rely on lip-reading, alternatives include “moving to the safer distance of two metres and removing the mask in order to facilitate communication, or the use of masks with a clear panel”.
Some experts have also shared concerns that wearing face coverings may give the wearer a false sense of security, although Prof Neal said there is “no evidence to suggest that is the case”.
Are some face masks better than others?
The WHO advises a three-layer face covering in the community – the outer layer should be water resistant, the inner should be water absorbent and the mid-layer acts as a filter.
It emphasises that a face covering alone cannot protect people from COVID-19, and must be combined with social distancing of at least a metre and regular hand washing.
The government has said coverings can be made from scarves, bandanas or other fabric items, as long as they cover the mouth and nose.
But scientists at the Leverhulme Centre, who studied different types of face coverings used by members of the public, say some coverings are not as effective as others, with loosely woven fabrics, such as scarves, shown to be the least effective.
Professor Melinda Mills, director of the Leverhulme Centre, said: “Attention must also be placed on how well it fits on the face; it should loop around the ears or around the back of the neck for better coverage.”
She added: “We find that masks made from high-quality material such as high-grade cotton, multiple layers and particularly hybrid constructions are effective.
“For instance, combining cotton and silk or flannel provide over 95 per cent filtration, so wearing a mask can protect others.”
What is the R value?The reproduction number – often called the R value or R number – is a measure of a disease’s ability to spread. It tells us how many people a single infected person will pass on the disease to.
The R number for COVID-19 that’s being quoted in the media and government briefings is what’s known as the ‘effective’ reproduction number. This value can go up and down.
Every disease also has what’s called a ‘basic’ reproduction number, R0, which is the fixed value of R if no measures are put in place. For example, measles is highly contagious, with a R0 as high as 18, while COVID-19 has a R0 of around three.
So if COVID-19 was allowed to spread through the population, an infected person would, on average, give the disease to three other people.
But if all these people are practising physical distancing, then the virus can’t spread so easily and the effective R value goes down.
The crucial thing is to keep R below 1. If we can do this, then the number of new cases dwindles and the outbreak will eventually come to a halt.
Conversely, if R rises above 1, then we run the risk of rapidly escalating case numbers that would require stronger measures to keep the virus under control.
Because of this, R is used by governments to assess how we are doing in our efforts to stop the spread of COVID-19, and to adjust our actions, if needed.
Amy is the Editorial Assistant at BBC Science Focus. Her BA degree specialised in science publishing and she has been working as a journalist since graduating in 2018. In 2020, Amy was named Editorial Assistant of the Year by the British Society of Magazine Editors. She looks after all things books, culture and media. Her interests range from natural history and wildlife, to women in STEM and accessibility tech.