A mutated coronavirus strain — not the original one that emerged in China — has become dominant worldwide.
A recent study suggested that mutated strain is more transmissible than the original based on research in cells.
But other scientists say there's not enough evidence yet to know if the strain is really more contagious, so it shouldn't be reason for concern.
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New research suggests that a mutated strain of the coronavirus that has become dominant worldwide is more contagious than the original virus that emerged in China.
A study published last week in the journal Cell found that this mutated strain — dubbed G614 — can infect human cells in the lab better than its predecessor.
The mutation that differentiates the strain is found the part of the virus' genome that codes for the shape of its spike protein. That's what the coronavirus uses to invade our cells, so it's possible that a tweak there could make it easier for the virus to infect our bodies.
But according to Emma Hodcroft, a geneticist at the Nextstrain project, there's no need to panic yet.
"Some headlines express this as a done deal. It's not. Most scientists are not that concerned about this at the moment," she told Business Insider.
Nextstrain tracks virus mutations over time and has been mapping the coronavirus' changes for months. Hodcroft said her team has yet to identify a mutation that would meaningfully change how lethal or infectious the virus is.
Such mutations, though possible, "happen over decades or centuries," she added.
A dominant form of the virus
Geneticists classify the original version of the coronavirus as the "D lineage," or D614. Strains with the G614 mutation are categorized as the "G lineage" and didn't crop up until February, according to a pre-print study released in May.
Since then, the G lineage has become more common in Europe, North America, and Australia, according to virologist Trevor Bedford, who works with Nextstrain. It seems to have edged out its D-lineage counterparts, which dominated in Asia.
The May study concluded that the G lineage was out-competing the D lineage, and therefore must be "a more transmissible form" of the coronavirus.
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But Bedford and Hodcroft don't see that as the only possible conclusion — the strain's dominance could just be due to circumstance.
Data shows that the G614 mutation arose just before the coronavirus spread to Europe. So the G lineage could have simply "gotten lucky," according to Bedford, and ended up being the version that spread to countries in Europe and North America. Many of those countries did not enact lockdowns for weeks after their first cases appeared, which allowed that version of the virus to proliferate.
Indeed, a preliminary study published in June found that no single mutation, including G614, was "convincingly associated with increased viral transmission."
G614 is more infectious in certain laboratory settings
To further investigate whether the G lineage of the coronavirus is more contagious, the researchers behind the new study measured how well the mutated coronavirus strain can invade human cells in a lab relative to its D lineage counterparts.
They engineered segments of the coronavirus with the G614 mutation, inserted those segments into a different type of virus called a lentivirus, then measured how well those synthetic virus particles could enter human cells in a laboratory dish. Those human cells were genetically altered to include the type of receptor, ACE2, that the coronavirus uses to invade a cell.
The results showed that that viruses containing the G614 mutation were three to six times more infectious.
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The study authors also examined 999 coronavirus patients from Sheffield, England, and found that people there infected with the G lineage virus harbored more of the virus in their respiratory tracts. People with higher viral loads may shed more virus, which can make them more contagious.
The scientists did not find, however, that patients infected with G614 were any more likely to require hospitalization than patients infected with D614.
Not all scientists are convinced
Some other preliminary research has also suggested that the G lineage mutation enhances the virus's ability to invade cells. But Hodcroft is still skeptical, since scientists still aren't sure whether observations at the cellular level necessarily apply to real people.
"We don't know how things we see in a lab scale up to a size of a full human. Transmissibility in cells and people are completely different ballgames," she said.
Nathan Grubaugh, an epidemiologist who was not involved with the new study, emphasized a similar point in a statement: Even though the G614 mutation may enable the virus to replicate better in cells, he said, "what we cannot say is that it is more transmissible or leads to more severe disease."
"We don't know if this has had any meaningful impact on the COVID-19 pandemic," Grubaugh added.
'It's rarely a case of one mutation'
All viruses mutate over time — as they replicate, minute errors are introduced into their genetic codes.
The Nextstrain project collects samples of the coronavirus from all over the world and sequences their genetic makeup, which helps researchers track its mutations over time.
According to Hodcroft, most of those mutations are innocuous: "meaningless changes to the virus's genetic instructions." But some — those that help a virus jump between species or infect more hosts — can affect the severity of an outbreak. Those are the types of mutations Nextstrain researchers are on the lookout for.
Hodcroft said it's very hard to predict which tiny changes at the genetic level could scale up to have detrimental consequences in a pandemic.
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But most often, she said, a solo mutation is not enough to lead the virus to change drastically.
"When viruses are adapting to a new host, it's rarely a case of one mutation. There are few things the virus has to have in a few places that, together, gives it the ability to infect a new cells, for example," she said.
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