20 February 2021 | New Scientist | 9important question to answer.”
There is reason to be optimistic.
Trials of a vaccine from Johnson &
Johnson show that while it was
less effective at preventing mild
or moderate disease in people
infected with P.1 or B.1.351 than
with past variants, it was just as
effective at preventing severe
disease, with no hospitalisations or
deaths in anyone given the vaccine.
This may be due to how
immunity works in the body.
Antibodies are crucial for
preventing infection in the first
place. They work by binding to
and blocking the part of the
coronavirus spike protein that
helps it get into cells. B.1.
and P.1 have several mutations,
including one called E484K, that
change the shape of this part,
which will help it to evade those
antibodies and could cause mild
or moderate illness.JOE
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newscientist.com/healthcheckWhat’s more, one study looking
at which mutations could help
the virus evade antibodies found
that the E484K mutation made
the biggest difference. So it may
be that we have already seen the
single worst mutation.
If so, we might not need to
tweak vaccines more than once
or twice, although of course we
cannot be sure of this. There is
still a chance that something
unpredictable could happen, such
as the virus, known as SARS-CoV-2,
recombining with another
coronavirus to produce a more
dangerous strain (see page 7).Cautious optimism
What we do know is that the four
human coronaviruses that have
long circulated in people cause
only mild illnesses. This is because
pretty much everyone is exposed
to them in childhood, and they
don’t cause severe illness in
children.
Since SARS-CoV-2 is also
very unlikely to make children
seriously ill, Lavine’s work
suggests that it will end up
doing the same.
It might be undergoing a
period of rapid evolution as it
adapts to a new host that is
starting to become immune, says
Lavine, but things should settle
down in the longer run. “The
prediction of it being mild in the
long term doesn’t change because
of the variants, it just pushes out
the time frame.”
Others are more cautious.
“Certainly, I think we can hope
this can be the case,” says Emma
Hodcroft at the University of Basel
in Switzerland. “But even if this
does become an endemic,
relatively harmless virus, how
long will that take? I think we
should prepare for optimistic
and slightly less-so scenarios.” ❚Once people are infected,
however, T-cells, which form part
of another branch of the immune
system, help mop up infected
cells, preventing severe disease.
Crucially, T-cells are effective as
long as they can recognise any part
of the spike protein. This means it
is much harder for the coronavirus
to evolve to evade T-cells.
The Pfizer/BioNTech vaccine
has been shown to produce a
strong T-cell response to B.1.351,
suggesting that it will remain
effective at preventing severe
disease even if it is less effective at
preventing infections.
Another reason for optimism
is that there is a limit to how
much the virus can evolve and
still function, says Lavine. For
instance, the virus won’t be able to
enter human cells if the part of the
spike protein that binds to them
changes too much.67%
Herd immunity threshold
with previous variants80-90%
Probable herd immunity threshold
with B.1.1.7, the current
dominant variant in the UK