Here’s why a variant of SARS-CoV-2 still reigns supreme: Shots


An electron microscope image shows a SARS-CoV-2 particle isolated early in the pandemic. It’s been nearly a year since the omicron was first detected, and scientists say this branch of the coronavirus family tree is still thriving.

NIAID/NIH via PA


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NIAID/NIH via PA


An electron microscope image shows a SARS-CoV-2 particle isolated early in the pandemic. It’s been nearly a year since the omicron was first detected, and scientists say this branch of the coronavirus family tree is still thriving.

NIAID/NIH via PA

Throughout the pandemic, the virus that causes COVID-19 has evolved rapidly, blinding the world with one variant after another.

But the World Health Organization has not given a Greek name to a variant of SARS-CoV-2 for nearly a year, a decision reserved for new variants that have or could have significant public health impacts. , such as being more transmissible or causing more severe effects. sickness.

This begs the question: has the evolution of the virus finally started to ebb, perhaps making it more predictable?

The answer — according to a dozen evolutionary biologists, virologists and immunologists interviewed by NPR — is no.

“SARS-CoV-2 continues to evolve extremely rapidly,” says Trevor Bedford, a computational biologist who studies virus evolution at the Fred Hutchinson Cancer Center in Seattle. “There is no evidence that evolution is slowing down.”

Instead, the most consequential evolutionary changes remained confined to the omicron family, rather than appearing in entirely new variants.

As the alpha, beta, gamma and other named variants sprouted new branches on the SARS-CoV-2 family tree, those members were eclipsed by the omicron branch, which is now dotted with a plethora of sub-variant stems.

“The omicron children – so the many children and direct cousins ​​within the diverse omicron family – these moved” as the dominant strains causing the pandemic, Emma explains Hodcroft, molecular epidemiologist at the University of Bern. “But this same family dominated” by outperforming other varieties.

One variant to rule them all

The ever-expanding brood of omicron maintained its dominance through what is called “convergent evolution when entities independently develop similar traits due to similar environmental pressures, according to Manon Ragonnet-Cronin, who studies viral genetics at the University of Chicago.

“We seem to be seeing evidence for large-scale convergent evolution for the first time,” says Ragonnet-Cronin. “We have what people call a swarm of omicron viruses, which have different ancestors within omicron, but have the same set of mutations.”

These mutations confer those descendants of omicron with the power they need most right now: the ability to sneak past the immunity people have built up after being infected, vaccinated, or both.

“When you see a convergence in evolution, it’s evolution’s way of saying ‘this mutation gets picked over and over because it’s really useful,'” says Jesse Bloom, computational biologist at Fred Hutchinson Cancer. Seattle Center.

These mutations in the virus’ spike protein have increased its ability to evade protective antibodies and continue to infect huge numbers of people.

“This virus gets a lot of lottery tickets if you will. And it seems like with these new variants, these new mutations are like the jackpot,” says Jeremy Kamil, an immunologist at Louisiana State University.

The Centers for Disease Control and Prevention currently tracks more than a dozen omicron subvariants, including BF.7, BQ.1, and BQ.1.1, some of which appear to be among the most immune to date.

Fortunately, the immunity people have built up through vaccination and infection still seems to protect the most against serious illness and death.

But the most recent the highly contagious omicron subvariants could help cause a new outbreak. They also give the virus plenty of chances to reproduce, mutate and evolve even further.

A family tree still full of surprises?

While all of this sounds dire, omicron’s long period of dominance gives some scientists hope.

The virus could, in a relatively optimistic scenario, continue to evolve this way for a long time, drifting in more subtle evolutionary directions like the flu, without sudden changes in its behavior that would make it more dangerous.

“The fact that we may have come out of a phase [in the pandemic] where we get completely new viruses from different parts of the tree invading and dominating could be a sign that we are heading towards some kind of more stable future for the virus,” says Hodcroft.

But that would mean large numbers of people would still catch the virus. Many would still fall seriously ill, die, or end up with long COVID. And because the virus is still so new, it’s impossible to know how the virus might evolve in the future, experts tell NPR.

“We are literally dealing with a completely new virus here,” says Kristian Andersen, immunologist at Scripps Research. “We don’t know how many other paths this particular virus might have. We just don’t know at this point.”

There’s no way to rule out, for example, the possibility that a radically different variant could reappear, perhaps after simmering inside someone with a weakened immune system who can’t drive out the virus. This allows the virus to broadly interact with the human immune system and find even more advantageous mutations.

“I guarantee you there are people who have been persistently infected with delta and alpha who have really weird combinations of mutations,” says Michael Worobey, an evolutionary biologist at the University of Arizona. “And I’m fully prepared for a delta- or alpha-based omicron-like event where one of these zombie viruses that’s been simmering in someone emerges.”

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