May 11, 2021

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Coronavirus variants: What are they, how dangerous are they? Here’s everything you need to know

The discovery of two variants of coronavirus has triggered alarm.

Scientists are
racing to find out whether these variants are more transmissible or could
present challenges for the Covid vaccine.

All viruses
naturally mutate, and Sars-CoV-2 is no exception, accumulating an estimated one
or two changes a month.

Mutations are
usually a chance event that will have little impact on the properties of a
virus, says Dr Lucy van Dorp, an expert in the evolution of pathogens at
University College London.

“The very
vast majority of mutations which we observe in genomes of Sars-CoV-2 are there
as passengers,” she says.

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“They don’t
change the behaviour of the virus, they are just carried along.”

But every once
in a while, a virus strikes lucky by mutating in a way that positively affects
its ability to survive and reproduce.

“Viruses
carrying these mutations can then increase in frequency due to natural
selection, given the right epidemiological settings,” Dr van Dorp says.

There is now a
frantic push to work out if this is the case for the variant first detected in
the UK (B.1.1.7 or VUI-202012/01), which appears to be spreading unusually
fast.

A similar but
unrelated variant has emerged in South Africa, with a small number of cases now
reported in the UK.

The fact both
have mutations in a gene that encodes the spike protein, which the virus uses
to latch on to and enter human cells, is particularly worrisome.

The UK variant
has 14 mutations that cause a change in protein building blocks (amino acids)
and three deletions (missing bits of genetic code).

According to the
World Health Organization (WHO), some may influence how fast the virus spreads.

  • One
    mutation in the spike protein (known as N501Y) has been detected in several
    variants, including the one from South Africa. Lab experiments suggest this
    mutation may help the virus bind to human cells, according to the Centers for
    Disease Control and Prevention (CDC).
  • Another
    mutation in the spike protein (P681H) is thought to be of “biological
    significance”, according to the WHO
  • A
    deletion (at position 69-70) has been linked in the past to mink farm outbreaks
    and in patients with weakened immune systems who can incubate the virus for
    several months

The deletion may
give some clues to how the variant evolved, perhaps in a patient with a
weakened immune system who was unable to fight off the virus enabling it to
linger in the body for several months, accumulating mutations along the way.

“The
current thinking is it’s evolved so many mutations in the context of a chronic
infection,” says Prof David Robertson of the University of Glasgow, who is
part of the Cog UK (Covid-19 Genomics UK Consortium), which has analysed the
new variant.

A connection
with mink is thought highly unlikely. “There’s no evidence mink, or any
other animals, are involved but it seems sensible not to rule it out,”
says Prof Robertson.

Scientists are
now hurrying to find out more about the mutations seen in the UK variant, which
has also been spotted in Australia, Denmark, Italy, Iceland and the
Netherlands.

The variant
found in South Africa, which has one of the same mutations, is also causing
concern. It shares the same mutation in the spike protein (N501Y) but has
arisen separately. Other mutations are being investigated.

There are strong
suspicions both variants may be spreading faster than expected, but this is
still unclear.

Sars-CoV-2 has
been at the heart of an unprecedented international scientific effort since
early January, when researchers in China released the first genome sequence.

Scientists have
now sequenced over 250,000 Sars-CoV-2 genomes, which have been shared on open
data platforms.

By taking a swab
from an infected patient, the genetic code of the virus can be extracted and
amplified before being “read” using a sequencer.

The string of
letters, or nucleotides, allows genomes and mutations to be compared.

“It is
thanks to these efforts, and UK testing laboratories, that the UK variant has
been flagged so quickly as a potential cause of concern,” Dr van Dorp
says.

Scientific
information is now being shared at an astonishing rate.

A key question
is whether the mutations might have implications for the effectiveness of
vaccines, although many experts consider this unlikely, at least in the short
term.

“This will
become increasingly important as vaccines are rolled out so that any plausible
candidates can be identified early, followed up and tracked,” Dr van Dorp
says.

“Longer-term
we may be required to reassess the composition of the vaccine and its delivery
strategy, so these efforts will be vital. Though for now, it is too early to
say.”

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