New evidence has emerged from China indicating that the large majority of coronavirus infections do not result in symptoms.
Chinese authorities began publishing daily figures on 1
April on the number of new coronavirus cases that are asymptomatic, with
the first day’s figures suggesting that around four in five coronavirus
infections caused no illness. Many experts believe that unnoticed,
asymptomatic cases of coronavirus infection could be an important source
of contagion.
A total of 130 of 166 new infections (78%) identified in the
24 hours to the afternoon of Wednesday 1 April were asymptomatic, said
China’s National Health Commission. And most of the 36 cases in which
patients showed symptoms involved arrivals from overseas, down from 48
the previous day, the commission said.
China is rigorously testing arrivals from overseas for fear of importing a fresh outbreak of covid-19.
Tom Jefferson, an epidemiologist and honorary research
fellow at the Centre for Evidence-Based Medicine at the University of
Oxford, said the findings were “very, very important.” He told The BMJ,
“The sample is small, and more data will become available. Also, it’s
not clear exactly how these cases were identified. But let’s just say
they are generalisable. And even if they are 10% out, then this suggests
the virus is everywhere. If—and I stress, if—the results are
representative, then we have to ask, ‘What the hell are we locking down
for?’”
Jefferson said that it was quite likely that the virus had
been circulating for longer than generally believed and that large
swathes of the population had already been exposed.
Users of Chinese social media have expressed fears that
carriers with no symptoms could be spreading the virus unknowingly,
especially now that infections have subsided and authorities have eased
curbs on travel for people in previous hotspots in the epidemic.
Zhong Nanshan, a senior medical adviser to the Chinese
government, said that asymptomatic infections would not be able to cause
another major outbreak of covid-19 if such people were kept in
isolation. Officials have said this is usually for 14 days.
Nanshan said that once asymptomatic infected people were
identified, they and their contacts would be isolated and kept under
observation.
Citing classified data, the South China Morning Post said that China had already found more than 43 000 cases of asymptomatic infection through contact tracing.
The latest findings seem to contradict a World Health
Organization report in February that was based on covid-19 in China.
This suggested that “the proportion of truly asymptomatic infections is
unclear but appears to be relatively rare and does not appear to be a
major driver of transmission.”1
But since that WHO report other researchers, including
Sergio Romagnani, a professor of clinical immunology at the University
of Florence, have said they have evidence that most people infected by
the virus do not show symptoms. Romagnani led the research that showed
that blanket testing in a completely isolated village of roughly 3000
people in northern Italy saw the number of people with covid-19 symptoms
fall by over 90% within 10 days by isolating people who were
symptomatic and those who were asymptomatic.2
In an article on the website of the Centre for
Evidence-Based Medicine, Jefferson and Carl Heneghan, director of the
centre and editor of BMJ EBM, write, “There can be little doubt
that covid-19 may be far more widely distributed than some may believe.
Lockdown is going to bankrupt all of us and our descendants and is
unlikely at this point to slow or halt viral circulation as the genie is
out of the bottle.
“What the current situation boils down to is this: is
economic meltdown a price worth paying to halt or delay what is already
amongst us?”3
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