"This is a, I would say, senseless dividing line," said
Doug Burgum, governor of North Dakota, his voice
catching as he talked of the rows that have broken
out in his state over the wearing of face-coverings.
There are similar spats elsewhere in America, for
masks have become the latest aspect of the culture
war that has emerged there over how to deal with
covid-19. Some shops refuse entry to maskwearers
and Mike DeWine, the governor of Ohio,
has rescinded an order requiring people to wear them,
saying that he "went too far". Elsewhere in the world,
by contrast, there is increasing acceptance that mask-
wearing is a good thing. On May 5th, for example,
the Royal Society, Britain's top science
academy, concluded that masks "could be an
important tool for managing community
transmission". This is not so much because they
protect the wearer--the normal reason people may put
them on in times of pestilence-- but rather because
they stop the wearer infecting others. In this context
covid-19's particular peculiarlty--that people who test
positive for it often do not have symptoms--is
important. Research published last month in Nature
Medicine, by Xi He of Guangzhou Medical
University and Eric Lau of Hong Kong University,
suggests that 44% of cases are caused by
transmission from people without symptoms at the
time of transmission. Those who do have symptoms
should not, of course, be out and about at all. In their
case masks are irrelevant. But to break the chain, it
behoves even the symptomless to assume that they
might be infected. Covid-19 is transmitted, above all,
by virus-laden droplets of spit. Experiments show
that face-coverings as simple as tea-towels are
effective. One study found that a tea-towel worn
around the face captured 60% of droplets. At 75%, a
surgical mask did better, but not overwhelmingly so.
Governments are beginning to take this on board. As
part of the loosening their lockdown, the Dutch are
required to wear face-coverings on public transport--
but not ones of medical grade, which should be
reserved for professionals. This encourages people to
make their own. Neither laboratory studies nor the
data on asymptomatic transmission provide
watertight evidence of the efficacy of masks. That
would need randomised controlled trials, in which
one group wore masks and the other did not. This
would be ethically tricky, since it might condemn
one of the groups to a higher death rate. Hamsters,
which are susceptible to covid-19, are the next best
thing to people. So researchers at Hong Kong
University put cages of healthy hamsters next to
cages of infected ones, with a fan in between drawing
air from the infected to the healthy cage. They
sometimes also placed a stretched-out face mask in
the air stream. With no interposed mask, two-thirds
of the healthy hamsters were infected within a week.
With a mask interposed close to the healthy hamsters
(the equivalent of a healthy person wearing a mask),
one-third were. With the mask close to the infected
hamsters, only a sixth were.
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