Every expert opinion on wearing masks
TO WEAR OR NOT TO WEAR
Every expert opinion you’ve heard about wearing masks is right
Should you wear a mask to stop the coronavirus? It’s a fraught question. Depending on where you live, the act risks social censure, accusations of selfishness, and perhaps the infection itself. No one wants to say they don’t know.
Asking eight health authorities will elicit eight different answers.
A brief review of health agencies’ recommendations for the coronavirus
from around the world adds to the confusion. In China, the government
has told almost everyone to wear disposable masks (and sometimes mandated it).
In Japan and Hong Kong, anyone entering crowded places are asked to don
them. In the West, the message is the opposite. Germany’s Federal
Ministry of Health warns mask wearers risk lulling themselves into a
“false sense of security.” American’s top health official, battling a
catastrophic shortage of masks for healthcare workers, has tweeted for people to “STOP BUYING MASKS! They are NOT effective in preventing the general public from catching #Coronavirus.”
For the public, the situation is maddening. In the US, officials appear to be managing scarcity rather than speaking honestly about masks’ effectiveness. In Asia, public health officials call it “common sense” and even designed homemade versions
for people to fashion from paper towels. Researchers who see no
evidence for their effectiveness in the general population, when
pressed, will take a deep breath and admit wearing masks themselves.
REUTERS/Michele Tantussi
What can scientists say with certainty? The literature is unequivocal on one point: Masks protect healthcare workers
from high levels of viral pathogens. From the lowly paper mask to
ultra-high filtration N95 masks designed to stop aerosols, decades of
studies show masks stop healthcare workers from getting infected in
hospitals, and prevent sick people from spreading disease to others.
As for whether everyone should wear a mask to slow a pandemic, the answer is far less clear.
Epidemiologists
cannot point to any conclusive evidence after years of studies. Almost
all the research suffers from small sample sizes or confounding
variables that distort results. “It’s all a little mysterious, but
that’s science for you,” says Andrew Noymer, a public health professor
at the University of California Irvine. “People look to science for
really crisp advice. Scientists often spend their lives arguing with
each other about shades of grey.”
That argument is now about saving lives.
What we know for sure
The coronavirus, like influenza and other viruses, spreads through the diffusion of millions of tiny viral particles.
After someone coughs, sneezes, or touches an object, these particles
can settle on a surface or hang briefly in the air, primarily in droplets.
Viral particles, as many as tens of thousand per droplet, can gain
access through our nose, mouth, or eyes after we touch our face or
breathe while in close contact with someone who is contagious. If the
dose is high enough—and a single droplet may do it—the virus can
replicate in our body, starting the infection cycle again.
Almost every version of manufactured masks, from every day surgical masks to N95 respirators appear to confer at least some level of protection against this transmission. Study after study has confirmed that in hospitals. 1
1
Most
studies found no difference between surgical masks and N-95s, but a few
found N95s performed somewhat better. As with much else in the field,
the science here is a bit muddy: "The advocacy of mask types is not
entirely evidence-based,” said researchers from the University of New
South Wales in a 2010 study. See a summary of studies here:
https://docs.google.com/document/d/1v5MkNfURbnFqzqeQ0Jm-O6_t7A4-zkNfKgqkheazXwo/edit?usp=sharing
REUTERS/Eduard Korniyenko
Masks
can work at home as well. Both the World Health Organization (WHO) and
the US Centers for Disease Control and Prevention (CDC) advise mask use
for people caring for those with Covid-19, as well as those infected.
But
this is where the evidence becomes less clear. One 2009 CDC study
showed masks could cut caretakers’ risk of viral infection by 60% to 80%—but less than half of people in the study wore their masks consistently. Some other studies have noted no effects within households.
At a population scale, the impacts of mask usage are still murkier. One of the largest attempts
to measure mask efficacy was at the University of Michigan during the
2007–2008 influenza season. Researchers divided 1,178 students into
three groups: One group was asked to wear face masks at least six hours
per day in their dorm, a second received masks plus hand sanitizer, and a
third served as controls. While hand sanitizer appeared to have an
effect, it wasn’t statistically significant, and masks alone showed no
effect at all. A 2012 analysis by London’s Health Protection Agency that reviewed 17 studies also failed to find conclusive evidence that wearing masks prevents influenza infection.
The
reasons for those results—how people wear masks, the nature of
influenza, differences in cultural norms, or something else entirely—is
impossible to ascertain for now. Why? “The science in support of masks
keeping us from getting infected is not strong,” concludes Jared Baeten,
a vice-dean at the University of Washington’s school of public health.
Studies
on masks’ efficacy are extraordinarily difficult to do. Enlisting
millions of people to wear masks during flu season, and comparing their
infection rates to people who do not, simply hasn’t been done—nor could
it, really. That’s left scientists struggling to compare observational
studies from places such as Asia (where mask-wearing is prevalent) with
places like the US or Europe where it is not. Drawing statistically
valid comparisons is difficult, if not impossible.
Mathematical models offer one form of clarity. When just 50% of the population wears masks, say researchers simulating outbreaks,
the share of the population infected by the virus is cut in half. Once
80% of the population wears a mask, it theoretically stops an outbreak
in its tracks. “Any type of general mask use is likely to decrease viral
exposure and infection risk on a population level, despite imperfect
fit and imperfect adherence,” notes a 2008 study by the Netherland’s National Institute for Public Health and the Environment.
But
all of this is highly theoretical, says Matthew Lamb, an epidemiologist
at Columbia University’s Mailman School of Public Health. Since humans
and viruses are messier than computer models tend to acknowledge, these
findings fall apart in the real world.
“Modelers
estimate that masks may help, but when studies are actually done in a
general population there isn’t any real population effect,” says Lamb,
an infectious disease prevention specialist. “The problem may be a lack
of good studies or that the modeling assumptions are optimistic.”
Give a first opinion
That doesn’t mean public health officials must remain on the fence. The first line of defense
will always be social distancing, hand-washing, sterilizing surfaces,
and avoiding touching one’s face. But researchers in the medical journal
The Lancet argue that (pdf) health agencies must consider asking the public to wear masks, even without strong evidence.
“It
is time for governments and public health agencies to make rational
recommendations on appropriate face mask use,” they wrote on March 20.
“There is an essential distinction between absence of evidence and
evidence of absence.” As a result, they argue it’s now “reasonable to
suggest” surgical masks for all vulnerable individuals in crowded,
high-risk places.
For Covid-19, this precaution is
especially reasonable. Many people are contagious before they fall sick,
or show any symptoms at all. Asian nations including South Korea,
Taiwan, Singapore, and China have beaten back outbreaks through a
combination of mass testing, contact tracing, and social distancing.
Widespread use of masks in Asia, where it is considered a civic duty
thanks to a century-long history of wearing masks
to cope with epidemics, may cut down on viral transmissions in crowded,
dense urban environments. At the peak of the 2003 SARS epidemic in Hong
Kong, 76% of the population wore a face mask. In the coronavirus pandemic, surveys by Hong Kong health authorities suggest 97.5% of the general adult population wears masks when leaving the house.
None
of this comes without risks. The US could manufacture or import
millions (ultimately, billions of masks) and embark on a mass education
campaign. “That’s a big risk” in the West, says Baeten, if it leads to
more risky behavior because people assume they’re safe and adherence is
low, eliminating any benefits of wearing masks.
To
really answer this question, governments need to study the question more
seriously. The scientific literature is littered with small experiments
and haphazard observations. Recruiting a few hundred college
undergraduates for an experiment will never be enough.
The
uncertainty has left countries like the US in agonizing straits.
Doctors and nurses who need masks right now are left to battle the
epidemic unprotected. Masks cannot be found at any price with stockpiles
exhausted and panic buying emptying warehouses.
The public is left hoping the medical professional who care for them
are protected, even as they try to protect themselves. Some have started donating their masks to hospitals.
Definitive
answers are only possible if scientists can conduct population-trials
among many thousands of people over several flu seasons. No one has ever
done such a study. But doctors are learning quickly in the midst of the pandemic, and it may change our desire to answer the question once and for all.
“I
don’t think we’ll have crisp answers by the end of this,” says Noymer.
“I do think there will be more willingness to study it.”
https://qz.com/1826717/do-masks-protect-against-coronavirus/
Comments
Post a Comment