The first thing to know is that there's not a lot to know. Sure, it just seems to make sense that if the coronavirus spreads mainly by droplets, and face masks block some ingoing and outgoing droplets, they should help. But if you try to live an evidence-based life, you're going to be disappointed when you look for good data about how well masks worn by the general public can stem the spread of viruses.
So let's do the best we can: Ask a leading expert for his thoughts. Dr. Ben Cowling is a professor of infectious disease epidemiology at the University of Hong Kong, living in a society where just about everybody is wearing a mask in public these days. His bottom line might be summed up this way: Face masks likely help somewhat, but if there's a choice between wearing a mask to a crowded space or staying home, definitely better to stay home.
How would you describe the state of the science on surgical/simple face masks protecting us against getting infected and infecting others? Clearly much more research needs to be done, but what should we conclude in the meantime, and most of all, what should we do?
Let's take one step back and think about all the different measures that we could use to prevent transmission of respiratory viruses. The two measures which are most studied, particularly with randomized controlled trials — our best quality of scientific evidence for whether something works or not — are hand hygiene and surgical face masks.
For face masks, there have been a few randomized trials and, as with hand hygiene, the evidence is quite mixed. In general, there's not a large benefit of wearing surgical face masks either for people who are sick or for other people who just want to protect themselves against getting infected.
My conclusion of the research is that perhaps there's a small effect, maybe a 5% or 10% reduction in the risk of transmission if people wear face masks. Probably not a very large effect.
There's a mechanistic reason to believe that face masks will do something. And I would note that we do recommend that health care workers wear surgical face masks. So there must be a reason why we do that. We must have some idea that there's effectiveness for health care workers. There must be some physiological reason why face masks can prevent infection or prevent transmission. But the scientific evidence is mixed and limited.
So what should we conclude in the meantime, and most of all, what should we do? I published an article in Lancet Respiratory Medicine very recently suggesting that we think rationally about face masks. The first priority is to make sure we have enough supply for health care workers, and there are particular types of face masks and particular standards for the face masks that should be worn by health care workers.
After that, I know the World Health Organization recommends that people should wear a face mask if they're sick. I would suggest that we go a little bit further and maybe consider recommending that older adults or vulnerable individuals consider wearing face masks, particularly if they're going to crowded areas, because those are the groups of people that would face the highest risk of a more severe infection if they were to get infected, and those are the group that we would like to protect the most.
Your latest paper finds a stunning level of face mask usage in Hong Kong — all but universal. Is there any reason to believe it has contributed to the measure of success there at getting the virus spread under control, and if so, what would be your best guess as to how much it contributed?
In Hong Kong, we have now 99% of people wearing face masks in the community, on the street, in public transport and often still indoors in offices as well, though not in their own homes usually. I'm sure that it's made a contribution, but I don't think it's the most important thing that we've done.
I think in Hong Kong, the scaling up of laboratory testing, isolation of cases, tracing their contacts and quarantine of the contacts are probably the most important public health measures in controlling transmission in the community.
And then in the community as a whole, we've also done a number of social distancing measures. We have school closures. We have lots of people working at home. And the streets are often quite quiet. People spend a lot more time at home voluntarily than they would normally do. That's probably the most important measure in the community.
But then when people do go out, they wear face masks and it must be contributing something. I don't know how much, but it must be doing something more than nothing.
Given what we know and don’t know, do "do-it-yourself" masks make sense, and if so, under what circumstances?
I'm reluctant to recommend do-it-yourself, made-at-home masks because we really don't understand their properties and how well they'll be working, and it's possible that they might not be any use at all, in which case it may be no use to make them.
There's some suggestion sometimes that wearing a mask wrongly or doing something wrong with a mask could increase your risk of infection. I think in general that's not really the case.
But for homemade masks, I guess if you have a choice between staying at home or going out into a crowded area with a homemade mask, maybe going out with a homemade mask would be a worse idea than just staying at home, in terms of protecting yourself against getting infected and also as a community acting together to reduce transmission in the community as a whole.
Is there now social censure of people who don’t wear masks in Hong Kong? Was there active social engineering to make face masks the norm there, and can you imagine such tactics working in America?
There certainly was not social engineering to promote face mask use. If anything, the government has been reluctant to encourage face mask use in Hong Kong. But there's been a social movement in the community where everybody decides to wear face masks because there's the idea that it will have some benefit to the whole community.
There is some criticism of people who don't wear masks in Hong Kong. Mask use is a little bit more common here to start with, but we've never seen anything like 99% wearing of masks before. We've measured it in previous epidemics. In 2009, it was something like 50%, and now it's up to 99% with COVID-19.
We do, of course, have limitations in the supply of face masks and the availability of face masks. Not everybody can get masks. And we've been using the same mask over and over again, which may not be the best idea, but that's the solution when you have limited amounts -- you re-use it and extend the life.
Is there any reason to think wearing face masks can cause harm in any way?
There's an argument in hospital infection control, as I understand it, that sometimes if you have too much protective equipment — full body suit and gloves and goggles and face visor and different masks and and all sorts of other equipment — you might actually put yourself at risk, because if that complex equipment gets contaminated when you're taking it off, you might unfortunately increase your risk of getting infected. For face masks, I don't think the same kind of thing applies.
I know that if you wear the face mask wrong, it won't provide as much protection as if you wear it correctly. So, for example, if you wear a surgical mask and it doesn't cover your nose, it's not going to provide as much protection as if it were covering your nose. If you touch the outside of it all the time, that's not going to help because the outside is where the virus might have been captured by the mask. So if you touch the outside and then you pick your nose or suck your finger, then you've kind of defeated the objective of wearing a mask in the first place.
What we recognize now, with the coronavirus pandemic, is that we actually do need these non-pharmaceutical interventions to play a much bigger role, maybe for longer.
I think the other thing to be careful of is if people have got choices about whether to go out or not and they might tend to stay at home if they don't wear a mask — and that's true in Hong Kong, where if they have a mask, they go out to a crowded area — I think actually it would be better to just stay at home if you can, because that's the best way to reduce your risk of getting infected.
Final question: Why has the research been so mixed and limited?
It's difficult to do studies on face masks, and they're not as exciting to funding bodies as antiviral trials or vaccine trials, because face masks seem like really a simple intervention. So we don't have a lot to go on.
I think after this pandemic, there's going to be renewed enthusiasm for looking at simple interventions. When we thought about influenza pandemics in the future, we've always had in mind that we've got antiviral drugs that should work, and we also have the potential to have a vaccine in six months so we just need some non-pharmaceutical interventions that can last for maybe a few months to slow transmission.
What we recognize now, with the coronavirus pandemic, is that we actually do need these non-pharmaceutical interventions to play a much bigger role, maybe for longer. We don't have an antiviral drug yet, we won't have a vaccine for a while, so really there's a much bigger potential role for distancing measures and maybe personal protective measures like hand hygiene, and perhaps also like face masks.
This interview has been lightly edited.
This segment aired on March 25, 2020.