When to wear a mask and when you can skip it
- A consensus is finally starting to form that there’s a negligible risk outdoors away from other people,
- Common sense would suggest that if an activity poses negligible risk, then wearing a mask offers only a negligible benefit, and should be optional. ·
- Science has a lot to say about the effectiveness of wearing a mask to stop the spread of the coronavirus, but the communication of that science has been corrupted by a combination of partisan divides, sensationalist media stories, distrust, false dichotomies, and letting the perfect be the enemy of the good.
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The studies on masks aren’t perfectly
definitive, but that’s typical of many issues involving health risks
— from mercury contamination to cancer screenings. It’s still better to
make decisions based on an incomplete body of evidence than to ignore evidence
altogether. In this case, it helps to add a dose of situational awareness and
common sense.
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The public health community got off on the wrong
foot with masks by advising against wearing them and then making a sudden
flip-flop and telling us not to leave home without them. Further complicating
the picture is a mix of people’s individual attitudes. Some members of the
public still fear the virus and want to remain safe, and others are at peace with
their risk but want some guidance on how to be a good citizen — or at
least be perceived as one.
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There have been reasonably convincing studies
showing that masks stop some of the particles that might carry the virus out of
people’s mouths. That suggests masks’ potential to protect others. Then there
are observational studies, which look at mask use in the real world.
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On June 1, The Lancet published an
analysis of 172 such studies, many of them done in health care settings. The
authors concluded that mask-wearing combined with eye protection and social
distancing could cut down on the spread of the virus, though the authors
admitted to a high degree of uncertainty.
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Another study came down on the side of mandatory
mask-wearing by watching disease trends in Wuhan and New York City. But some
other researchers noted flaws in that study, published in the Proceeding of the
National Academy of Sciences. The one-to-two-week delay between infection
and test results would suggest infections in New York City dropped well before
masks were made mandatory. Some experts wanted the study retracted.
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When there are multiple changes in behavior
going on at the same time, it can be impossible to connect any one of those
changes to rising or falling case numbers.
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That doesn’t mean the information in those
studies can’t be useful. Physician and infectious disease specialist Muge
Cevik, who has been a prescient guide to relative risks, pointed out to me that
mask-wearing should be informed by other studies on how the virus spreads. A
consensus is finally starting to form that there’s a negligible risk outdoors
away from other people, and that very brief encounters pose very little risk,
such as people walking, running or cycling past you.
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Common sense would suggest that if an activity
poses negligible risk, then wearing a mask offers only a negligible benefit,
and should be optional.
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On the other extreme are potential
super-spreading events — anywhere many people are confined indoors,
especially if there’s close contact. Trump’s planned Oklahoma rally is a good
example. There, common sense would dictate that such events should not take
place at all.
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Then there’s the middle ground. Mask wearing is
likely to do the most good in settings where people have little choice but to
interact in enclosed spaces — grocery shopping, riding public transportation,
ride-sharing, getting a haircut, or seeing a doctor.
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Also in this middle category is gathering
outdoors in large groups — such as at a protest. If most protestors wear a
mask at all times, this will likely reduce transmissions.
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Cevik, who works at the University of St.
Andrews in the U.K., pointed out that the six-foot rule applies best
outdoors, while in badly ventilated indoor settings, aerosol particles might
accumulate and put people at risk even if they never get that close to others.
And length of exposure matters a lot, so bus drivers, haircutters and store
clerks face a much higher risk than their customers. Their risk very likely
goes down if customers wear masks.
Then there’s a problematic category
of activities, such as eating in restaurants, where masks can’t be worn
consistently. Would diners be stuck trying to pull masks on and off with every
bite? Some experts say such “fiddling" with masks is only going to spread
any viruses the mask has captured. As a compromise, many restaurants are seating
people outdoors and allowing them to keep masks off while eating. Gyms and yoga
studios pose a similar challenge.
The risks associated with close
contact and crowds seem obvious and intuitive. And yet Americans have been
fixated on the unlikely possibility that infectious doses of virus would fly
off cyclists or creep in on packages. In response, some have adopted irrational mask-wearing practices, such as keeping one on while riding
or driving, but pulling it down to congregate and chat with groups of people.
And it’s no surprise that politics
would infuse the issue, given the moral tone of the mask debate and different
messages on mainstream and conservative media. In the U.S., we have some
fraction of people wearing a mask all the time, and some fraction never wearing
one. It would be better if everyone wore one when it was likely to help.