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- You might have read
that the novel coronavirus is mutating.
That it's changing its genetic sequence as it spreads.
That's very true.
Scientists have examined the sequences
of hundreds of viruses taken from people around the world,
and some are starting to diverge from one another.
The term mutating coronavirus might sound alarming,
but it shouldn't be.
So far during this pandemic,
mutations have not been a bad thing.
In fact, they've been a bit useful.
- And we're gonna try to visualize why that is.
With an inkjet printer and a Sharpie.
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- A virus is essentially a loose strand
of genetic material surrounded by a protein-based wrapper.
Viruses exist to make copies of themselves.
They spread by entering a host
and hijacking its cells to replicate.
Mutations are a natural by-product of that process.
The protein that's in charge of making copies
of the virus' genes inside a cell,
called a polymerase, can make mistakes.
Sometimes it'll slip in an adenine
in a spot where there's supposed to be a guanine.
Other times, multiple different viruses
can also end up in the same host body.
If they both dump their genes into the same cell,
some bits and pieces can get swapped around,
and an entirely new virus is created.
That process is called recombination.
It was likely some kind of recombination event
that created the new coronavirus.
Scientists think that a coronavirus
from a bat swapped some genes with another coronavirus,
maybe from a different animal.
That may have triggered a change in the spike protein
on the virus, the part that binds to cells
and lets the virus hijack them.
In this case,
the protein became good at binding to human cells,
so when by chance it found itself in a human eye or nose,
it could easily latch onto a cell.
It started churning out copies of itself
and jumped to another person, and another,
until it spread around the globe.
Now that the virus is here,
future mutations could change how it acts, in theory.
Mutations that create beneficial traits
are more likely to stick around,
whereas those that could harm the virus tend to fade away.
For a virus, a beneficial mutation might be one
that helps it spread by staying airborne longer,
whereas a harmful mutation might be one
that kills its host too quickly,
limiting its opportunity to spread.
Those kinds of changes could happen with this virus,
but none of them seem to be happening.
A viral genome in New York City might look different
from one in Washington State,
but the viruses are functionally the same.
Someone who is infected with a New York virus
probably isn't going to be any better or worse off
than someone who was infected with a Washington virus.
There are different lineages of the virus,
but there don't seem to be different strains.
It's an important distinction.
A new strain would have a different biological property,
like staying airborne longer.
A few apparently neutral changes
to the genetic code don't meet that bar.
So why haven't new strains appeared?
Well, it's partly because this virus is comfortable.
It's already evolved in ways that make it really good
at thriving in humans and spreading between them.
So it's not under a lot of evolutionary pressure
to get even better at those things.
It also has to do with this particular type of virus.
The coronavirus is an RNA virus,
and those usually mutate fast.
Unlike DNA, RNA doesn't have built-in tools
to repair the mistakes made in the copying process.
But coronaviruses like this one
actually do have proofreaders built in.
They double-check that they're not making mistakes
when they copy themselves,
so they're less likely to slip in the wrong nucleotide.
That means today, virus samples
from all over the world look pretty similar
to the one that first emerged in Wuhan.
Many people who have COVID-19 are infected with viruses
that are less than 10 nucleotides different from any others.
The full genome is around 30,000 nucleotides long,
so those changes are pretty minuscule.
That's good for vaccines and treatments.
It means the virus isn't changing fast enough
that drugs and vaccines would stop working.
If a drug works now,
the specific bit of the virus it targets
is not likely to change or vanish.
But the pace of mutation, however slow, is useful to us.
It helps scientists track how and where the virus is moving.
If two people have the same mutation,
it could mean that their viruses are closely related,
and that they're part of a cluster of infections.
Mutations are how experts
were able to track New York's COVID-19 outbreak
back to a European lineage.
So mutations happen.
They're part of the natural rhythms of a virus.
They're not inherently good or bad.
Scientists are watching them closely,
but they're not expecting
a science-fictiony monster movie scenario.
What we see is probably what we're gonna get,
at least for a little while.
The challenge is understanding it.
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