As cases of covid-19 continue to rise, many people choose to wear a face mask when they're out in public – but are they working?
Are we all supposed to wear face masks?
Should members of the public wear face masks during the COVID-19 pandemic? It's a controversial issue, with different countries and authorities giving different advice.
We reviewed the results of more than a dozen randomized trials of facial masks and transmission of respiratory diseases. Current best evidence has shown that wearing a mask to prevent viral respiratory infections such as COVID-19 offers minimal protection, if any.
Conflicting Recommendations Two of the world's leading health organizations disagree on wearing masks. The World Health Organization (WHO) is currently deterring mask use: there is currently no evidence that wearing a mask (whether medical or other) by healthy people in the wider community, including universal community masking, can prevent them from becoming infected with respiratory viruses, including COVID-19.
WHO recommends special masks (N95 masks or equivalent) plus additional protection for health workers working with people who have or are suspected of having COVID-19.
By contrast, the Centers for Disease Control and Prevention (CDC) in the United States recently recommended that everyone wear a mask. However, this is to prevent infected people from passing on the infection, not to prevent the wearer from becoming infected.
Who's right, huh? Do you wear a mask to protect the wearer? Does that protect others?
To examine this, we need to first look at how coronavirus spreads and how masks might stop it.
010 mask graph The coronavirus can be transmitted directly. (Author provided) There are several possible pathways to infection. An infected person may cough, sneeze, or breathe within about two meters of another person, and the virus may land in the eyes, nose, or mouth of the other person (1).
Another route is when an infected person coughs or sneezes on his or her hand or on the surface. The uninfected person then shakes his hand (2a) or touches the surface (2b) and transfers the virus to his or her own eye, nose or mouth.
It is possible that an infected person may also cough or sneeze to cause airborne spread (3) beyond close contact – but it is controversial whether this last route is a major means of transmission.
We don't know how much COVID-19 transmission occurs on each of these routes. It is also unclear how much protection a mask would offer in each case.
Current best evidence To resolve this issue, we analyzed 14 randomized trials of mask wear and infection for influenza-like illnesses. (There are no randomized trials involving COVID-19 on their own, so the best we can do is look at similar diseases.) When we combined the results of these trials, which looked at the effect of masks versus no masks on health workers and the general population, they did not show that wearing masks would lead to a significant reduction in influenza-like illness. However, the studies were too small to rule out a minor effect on masks.
Why don't the wearer's masks protect?
There are several possible reasons why masks do not offer significant protection. First of all, masks may not do much without eye protection. We know from animal and laboratory experiments that influenza or other coronaviruses can enter the eyes and travel to the nose and the respiratory system.
Although standard and special masks provide incomplete protection, special masks combined with goggles appear to provide complete protection in laboratory experiments. However, there are no studies in real-world situations that measure the results of combined masks and eyewear.
The apparent minimal impact of wearing masks could also be that people did not use them properly. For example, one study found that less than half of the participants wore them “most of the time.” People may also wear masks improperly, or touch a contaminated part of the mask when it is removed and transfer the virus to their hands, then to their eyes, and thus to the nose.
Masks can also provide a false sense of security, meaning that wearers could do more risky things, such as going to crowded spaces and places.
Are the masks protecting others?
Could masks protect others from the virus that might have spread to the mask wearer? A recent Hong Kong laboratory study found that some evidence masks may prevent the spread of viruses from the wearer.
They took people with flu-like symptoms, gave half of them masks and half no masks, and collected viruses from the air they breathed out for 30 minutes, including coughs.
Masks reduced the amount of droplets and aerosols containing detectable amounts of viruses. But only 17 of the 111 subjects had coronavirus, not SARS-CoV-2 coronavirus. While the study is promising, it urgently needs to be repeated.
We also don't know how this reduction in aerosols and droplets translates into a reduction in infections in the real world. If there is an effect, it may be diluted by a number of factors, such as sick people who do not wear masks and “well” people who have no symptoms but still carry and spread the virus.
Masks for a few?
If wearing masks significantly reduces the spread of infection to others, what should we do? We could ask anyone with any respiratory symptoms to wear masks in public. This could complement other strategies such as social distancing, testing, tracking and tracing to reduce transmission.
We could also ask everyone to wear masks in indoor public spaces to capture infected people without symptoms. Outdoors is more difficult, as most people pose little or no risk. Perhaps, as we reduce restrictions, masks may also be required at some outdoor crowd events, such as sporting events or concerts.
Another possibility is the “2 x 2” rule: if you are outdoors and you have to wear a mask within 2 meters of other people for more than 2 minutes.
Mask worn for possibly infected persons, in order to prevent the spread of infection, warrants a rigorous and rapid investigation. It could be an alternative or supplement to social distances, hand hygiene, testing, and lockdowns. Face mask guidance varies widely between international health authorities and governments. The World Health Organization (WHO) currently only recommends face masks for people who are coughing or sneezing, or for those who are caring for people who are suspected of coviding-19.
In places like Lombardy, Italy's worst hit region, face masks are mandatory. The UK Government does not recommend widespread use of them, while the US Centers for Disease Control and Prevention recommended, as of 3 April, that people wear “cloth face coverings” when they leave – and even provide instructions on how to make one.
Part of the reason for recommending homemade face masks is that limited supplies of medical face masks have been reserved for healthcare workers, some of whom have had to resort to packing bin bags, snorkels and office supplies purchased from craft stores due to shortages.
Some have also used cloth face coverings, but they're not up to the job, says Raina MacIntyre at the University of New South Wales in Sydney.
In 2015, MacIntyre and her colleagues conducted a clinical trial pitting cloth masks against physicians. The team provided 1,607 health workers at 14 hospitals in Hanoi, Vietnam, with either disposable medical masks or reusable cloths that could be washed at home at the end of the day they were worn. The team found that those who wore cloth masks were significantly more likely to catch a virus.
But what about the rest of us, though? In an attempt to answer this question, Paul Hunter and his colleagues at the University of East Anglia, UK, looked at 31 published studies on the efficacy of facial masks.
Overall, the evidence suggests that wearing some kind of face cover may have a small benefit. They do seem to prevent the spread of the virus by sick people, but the evidence is weak and inconsistent, says Hunter.
“Our view is that there was some evidence of a degree of protection, but that wasn't great,” he says. “So we still don't know whether to face masks in community work.” Hunter believes there is enough evidence to support mask-wearing for some front-line staff, such as those working in public transport or supermarkets, as well as vulnerable people entering high-risk environments like hospitals on a temporary basis – as long as their use does not deprive healthcare workers of equipment.
An effective face mask is one that fits well around the nose, mouth, and chin, providing a seal that doesn't let air flow around the sides, she says. It must also filter out the particles that might contain the virus.
If you wear a mask, it is important to use it properly. It's easy to contaminate your own mask by touching or reusing it, for example. And don't let wearing a face mask give you a false sense of security: you can still get infected while you're wearing one, and it's often vital to wash your hands, whether you wear a mask or not.
Even if everyone followed this advice, it is not clear whether the widespread use of facial masks would have a significant impact on the spread of the virus. The WHO says that it “cooperates with research and development partners to better understand the effectiveness and effectiveness of non-medical masks.” “There's just not a lot of evidence in the community about cloth masks,” says MacIntyre.