Secondary school students will be expected to wear face coverings in class as part of measures introduced for the return of all pupils to schools in England from 8 March.
Updated guidance from the Department for Education recommends that face coverings be worn indoors “where social distancing cannot be maintained” and where the individual is not exempt. This includes in the classroom, as well as in corridors and communal areas.
But is wearing a mask really effective against the spread of the virus, and if so, under what conditions?
Why wear a face mask?
Professor Paul Digard is chair of virology at the University of Edinburgh, and was part of a team of researchers who conducted a recent study into the effectiveness of masks in preventing the transmission of Covid-19 (SARS-CoV-2).
Basic cotton or disposable masks – the kind that teachers and pupils are likely to have access to – are “probably not going to do much at protecting you directly from breathing in virus”, he admits.
However, what these masks can do is discourage the wearer from touching their face.
“People always play with their faces and nobody really realises how much they do it. Children are probably worse than adults, but not much,” Digard says. “So if you’re going to be infected by contact, by picking up virus on your fingers, it’s going to be because you’re playing with your face. A mask will stop you doing that to some extent.”
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The use of a cotton face mask is limited when it comes to protecting the wearer from becoming infected. However, these masks work well as a tool to prevent infectious people from spreading the virus too widely, Digard says.
He explains, though, that we need to be clear about the relative risks of the routes of transmission.
“Say I’m infected, and I’m sat in a room opposite you and we’re having this conversation face to face. I will be breathing virus out. Some of it will be floating around the room and you’ll breathe it in, but that will be low concentration,” he explains.
Any larger respiratory droplets that come out of a person’s mouth while they are talking also represent a relatively low chance of infection, he continues. The moment these droplets fall on to a surface, the virus will lose some of its infectivity, which will further reduce over time.
“So to be infected from the contaminated surface, it’s a chain of events,” he says. “I have to spit virus on to the table, you have to get it on your finger, you then have to transfer it from your finger to your nose, or your conjunctiva or whatever. It’s an unlikely chain, low-ish probability.”
Where the risk comes is when someone projects droplets, and here masks can dramatically reduce the chances of someone spreading the virus.
“If I happen to cough or sneeze on you, you’re going to get quite a dose on your face and breathe some of it in. That’s the high probability transmission rate. If I’m wearing a mask, even if it’s just a single-layer buffer, then that direct transmission is going to be 90 per cent or more blocked.”
Coronavirus: School guidelines for face masks
So, that’s why masks work. But what about how you wear them? Does that make a difference?
The government's updated guidance for schools sets out how to wear and remove masks safely and explains that this process must be clearly communicated to pupils, staff and visitors.
Their recommendations include that you should clean your hands before and after touching your mask; that you should avoid touching the front of your mask; that masks should be stored in “individual, sealable plastic bags” between uses; and that if a face covering becomes damp, it should not be worn.
The reason why you should avoid touching the front of your mask, Digard says, is because masks are frustratingly effective at collecting and containing the virus.
“Where a child is infectious, and is breathing out the virus, the mask will pick it up, because there’s a lot of data saying that masks really do work to block the spread of respiratory droplets which contain the virus,” he says.
“So, you can imagine the infected person will be dumping a load of virus into their mask. If they then touch the front of the mask when they take it off, they get it on their fingers and then when they touch the desk, door handles, whatever, then there’s infectious virus dumped on that surface.”
From that contaminated surface, it will then be possible for others to pick up the virus on their fingers and transfer it to themselves.
This explains why you should always wash your hands after taking the mask off, and why the guidance recommends storing your mask in a sealed bag between uses: if the mask is full of virus, the last thing you would want to do is put it into a pocket or a bag, transferring the virus to those surfaces, too.
As for why you shouldn’t wear your mask if it becomes damp, Digard says that this piece of advice can be explained by the way in which the fabric of the mask gathers the virus.
“If you look at mask fabrics under the microscope, they’re full of pores, and the pores are much bigger than the virus, but they work to filter stuff out because the virus doesn’t really come out as single, virus-size particles; it’s virus in bigger droplets of liquid, and the liquid tends to come out with a little bit of a charge on it, and it ends up sticking to the mask because of that charge.”
Over time, as you breathe and talk, these droplets of liquid will build up, making the fabric damp. And although Digard says that his research has shown that masks will catch the virus just as effectively when they’re wet as when they’re dry, the dampness will make it easier for the virus to transfer to your hands when you take it off or touch it.
But just how important is it that students and teachers follow this advice to the letter?
After all, doing so is likely to be a challenge in the middle of a busy school day. And if teachers are likely to struggle to tick all of these boxes, how about a class full of teenagers?
This shouldn’t matter, Digard says. The important thing is that you wear a mask in the first place; the rules around how you wear it come second.
“I think any use is good. It doesn’t have to be perfect,” he says.
“If you wanted to absolutely block the transmission then you’re talking about full medical-grade PPE [personal protective equipment], which is actually unwearable for long periods of time, even by the professionals who are trained how to use it. It’s just not feasible for daily life for the bulk population.
“So you’re working with an imperfect system, but it does help. And the more people stick to it, and the better that they stick to it, the better it will work and the lower the transmission. Every little bit helps.”