We looked at the results of more than a dozen randomized trials of face masks and the transmission of respiratory disease. We found that the best current evidence suggests that wearing a mask to prevent viral respiratory infections such as COVID-19 provides minimal protection, if necessary.
Two of the world’s leading health organizations disagree about wearing the mask. The World Health Organization (WHO) currently discourages the use of masks:
There is currently no evidence that the wearing of a mask (medical or otherwise) by healthy people in a broader community setting, including universal community masking, can prevent them from being infected with viruses respiratory systems, including COVID-19.
WHO recommends special masks (N95 masks or equivalent) and other protection for health workers working with people who have, or are suspected of having, COVID-19.
In contrast, the Centers for Disease Control and Prevention (CDC) in the United States recently recommended that everyone wear a (cloth) mask. However, this is to prevent infected people from spreading the infection, not to prevent the carrier from being infected.
Who is right? Does wearing a mask protect the wearer? Does it protect others?
Understanding the spread
To examine this, we must first look at how the coronavirus spreads and how masks could stop it.
There are several possible routes of infection. An infected person can cough, sneeze or breathe when they are about two meters from another person, and the virus lands in their eyes, nose or mouth (1).
Another way is when an infected person coughs or sneezes on their hand or on a surface. The uninfected person then shakes hands (2a) or touches the surface (2b) and transfers the virus to their own eyes, nose or mouth.
It is possible that an infected person may also cough or sneeze to create an airborne spread (3) beyond the area of close contact – but it is controversial that the latter is a major means of transmission.
We do not know how much transmission occurs on each of these routes for COVID-19. It is also unclear how much protection a mask would offer in each case.
Best Current Evidence
To resolve this issue, we analyzed 14 randomized trials of mask use and infection for influenza-like illness. (There are no randomized trials involving COVID-19 itself, so the best we can do is to look at similar diseases.)
When we combined the results of these trials which studied the effect of masks against the absence of masks in healthcare workers and the general population, they did not show that wearing masks leads to a substantial reduction in influenza-like illness. However, the studies were too small to rule out a minor effect for the masks.
Why don’t masks protect the wearer?
There are several possible reasons why masks do not offer significant protection. First, masks may not do much without eye protection. We know from animal and laboratory experiments that the flu or other coronaviruses can get into the eyes and travel to the nose and into the respiratory system.
While standard and special masks offer incomplete protection, special masks combined with glasses appear to offer full protection in laboratory experiments. However, there are no studies in real-world situations measuring the results of a mask and glasses combined.
The apparent minimal impact of wearing masks could also be due to people not using them properly. For example, one study found that less than half of the participants wore them “most of the time”. People can also wear masks inappropriately, or touch a contaminated part of the mask when it is removed and transfer the virus to their hand, then to their eyes and therefore to their nose.
Masks can also provide a false sense of security, which means that wearers can do more risky things, such as going to crowded spaces and places.
Do masks protect others?
Could masks protect others from the virus that could have been spread by the mask wearer? A recent laboratory study in Hong Kong found that certain evidence masks can prevent the spread of viruses by the wearer.
They took people with flu-like symptoms, gave half of them masks and half without masks, and for 30 minutes, they collected viruses from the air they exhaled, including cough.
The masks effectively reduced the amount of droplets and aerosols containing detectable amounts of virus. But only 17 of 111 subjects had a coronavirus, and it was not the SARS-CoV-2 coronavirus. Although the study is promising, it needs to be repeated urgently.
We also don’t know how this reduction in aerosols and droplets translates into a reduction in real-world infections. If there is an effect, it can be diluted by several factors such as sick people who do not wear a mask and “healthy” people who have no symptoms but still carry and spread the virus.
Masks for some?
If wearing masks dramatically reduces the spread of infection to others, what should we do? We could ask anyone with respiratory symptoms to wear masks in public. This could complement other strategies such as social distancing, testing, tracking and tracing to reduce transmission.
To also capture infected people without symptoms, we could ask everyone to wear masks in indoor public spaces. Outdoors, it’s more difficult, since most people pose little or no risk. Perhaps, as we are reducing the restrictions, masks may also be required during certain outdoor crowd events, such as sporting events or concerts.
Another possibility is a “2 x 2” rule: if you are outside and less than 2 meters from other people for more than 2 minutes, you must wear a mask.
Wearing a mask for potentially infected people, to avoid spreading the infection, warrants a rigorous and rapid investigation. It could be an alternative or a complement to social distance, hand hygiene, testing and lockouts.
The authors would like to thank John Conly, Liz Dooley, Lubna Al-Ansary, Susan Michie and Amanda McCullough for their comments.
Paul Glasziou, Professor of Medicine, Bond University and Chris Del Mar, Professor of Public Health, Bond University
This article is republished from The Conversation under a Creative Commons license. Read the original article.