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 New variants first detected in such far-flung countries as Brazil,
South Africa and Britain cropped up spontaneously within a few
months late last year. All three share some of the same mutations in
the important spike region of the virus used to enter and infect
cells.
These include the E484k mutation, nicknamed "Eek" by some scientists
for its apparent ability to evade natural immunity from previous
COVID-19 infection and to reduce protection offered by current
vaccines - all of which target the spike protein.
The appearance of similar mutations, independent of one another,
springing up in different parts of the globe shows the coronavirus
is undergoing "convergent evolution," according to a dozen
scientists interviewed by Reuters.
Although it will continue to mutate, immunologists and virologists
said they suspect this coronavirus has a fixed number of moves in
its arsenal.
The long-term impact for the virus' survival, and whether a limit on
the number of mutations makes it less dangerous, remains to be seen.
"It is plausible that this virus has a relatively limited number of
antibody escape mutations it can make before it has played all of
its cards, so to speak," said Shane Crotty, a virologist at the La
Jolla Institute for Immunology in San Diego.
That could enable drugmakers to stay on top of the virus as they
develop booster vaccines directly targeting current variants, while
governments struggle to tame a pandemic that has killed nearly 3
million people.
The idea that the virus could have a limited number of mutations has
been circulating among experts since early February, and gathered
momentum with the posting of a paper showing the spontaneous
appearance of seven variants in the United States, all in the same
region of the spike protein.
https://www.medrxiv.org/content/
10.1101/2021.02.12.21251658v1
EVOLUTION, IN REAL TIME
The process of different species independently evolving the same
traits that improve survival odds is central to evolutionary
biology. The vast scope of the coronavirus pandemic - with 127.3
million infections globally - allows scientists to observe it in
real time.
"If you wanted to sort of write a little textbook about viral
evolution, it's happening right now," Dr. Francis Collins, a
geneticist and director of the U.S. National Institutes of Health,
said in an interview.
Scientists saw the process on a smaller scale in 2018 as a dangerous
H7N9 bird flu virus in China appeared to begin adapting to human
hosts. But no pathogen has evolved under such global scrutiny as
SARS-CoV-2.
Wendy Barclay, a virologist and professor at Imperial College London
and a member of a scientific advisory panel to the UK government,
said she is struck by the "amazing amount of convergent evolution
we're seeing" with SARS-CoV-2.
"There are these infamous mutations - E484K, N501Y and K417N - which
all three variants of concern are accumulating. That, added
together, is very strong biology that this is the best version of
this virus in the given moment," Barclay said.
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 It's not that this coronavirus
is especially clever, scientists said. Each time
it infects people it makes copies of itself, and
with each copy it can make mistakes. While some
mistakes are insignificant one-offs, the ones
that give the coronavirus a survival advantage
tend to persist. "If it keeps
happening over and over again, it must be providing some real growth
advantage to this virus," Collins said.
Some specialists believe the virus may have a limited number of
mutations it can sustain before compromising its fitness - or
changing so much it is no longer the same virus.
"I don't think it's going to reinvent itself with extra teeth," said
Ian Jones, a professor of virology at Britain's University of
Reading.
"If it had an unlimited number of tricks...we would see an unlimited
number of mutants, but we don't,” said Michel Nussenzweig, an
immunologist at Rockefeller University in New York.
CAUTIOUS OPTIMISM
Scientists remain cautious, however, and say predicting how a virus
will mutate is challenging. If there are limits on how the
coronavirus can evolve, that would simplify things for vaccine
developers.
Novavax Inc is adapting its vaccine to target the South African
variant that in lab tests appeared to render current vaccines less
effective. Chief Executive Stan Erck said the virus can only change
so much and still bind to human hosts, and hopes the vaccine will
"cover the vast majority of strains that are circulating."
If not, Novavax can continue matching its vaccine to new variants,
he said.
Researchers are tracking the variants through data-sharing platforms
such as the Global Initiative on Sharing Avian Flu Data, which
houses a huge trove of coronavirus genomes.
Scientists recently identified seven U.S. coronavirus variants with
mutations all occurring in the same location in a key portion of the
virus, offering more evidence of convergent evolution.
Other teams are conducting experiments that expose the virus to
antibodies to force it to mutate. In many cases, the same mutations,
including the infamous E484K, appeared.
Such evidence adds to cautious optimism that mutations appear to
share many of the same traits.
But the world must continue tracking changes in the virus, experts
said, and choke off its ability to mutate by reducing transmission
through vaccinations and measures that limit its spread.
"It's shown a very strong set of opening moves," Vaughn Cooper, an
evolutionary biology specialist at the University of Pittsburgh
School of Medicine, said of this coronavirus. "We don't know what
the end game is going to look like."
(Reporting by Julie Steenhuysen in Chicago and Kate Kelland in
London; Editing by Josephine Mason and Bill Berkrot)
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