Why does the coronavirus keep mutating? Experts explain how Omicron and other variants emerge - The Boston Globe

The emergence of the Omicron coronavirus variant, which has set off alarms around the world and has now been detected in the United States, is the result of mutation, a natural process that will continue until more people are vaccinated around the world, experts say.

“It will never stop. As long as the virus is infecting something, it will keep mutating. That’s what viruses do. They mutate like everything else on the planet,” said Vincent Racaniello, a professor of microbiology and immunology at the Columbia University Vagelos College of Physicians and Surgeons.

Here’s how it works: The SARS-CoV-2 virus takes over cells and commandeers their machinery to make more virus. During the process, mistakes can be made in the copying of the virus. Those mistakes, or mutations, can result in new virus variants. Some of those variants will outcompete the others and proliferate.

“The mutations happen essentially by accident,” said Dr. Daniel Rhoads, section head of microbiology at the Cleveland Clinic. “The analogy is often given that if you type up notes and make a mistake in a keystroke, now you have a misspelled word.”

That could mar what you’ve written, he said, but “every now and then maybe you’ll stumble across a typo that’s actually advantageous. That’s kind of what happens to the virus. Every now and then one of these mistakes actually turn out to be advantageous,” helping the virus spread more easily.

That was the case with the Delta variant, which was first identified in India in late 2020 and now accounts for nearly 100 percent of COVID-19 cases in the United States. But the process of mutation didn’t stop there. Last week, scientists issued warnings about Omicron, and it was labeled a “variant of concern” by the World Health Organization.

“It won’t stop mutating because that’s the biology of an RNA virus,” Rhoads said, noting that many mutations may not have a major effect on how the virus behaves.

Racaniello said the process of mutation and the rise of mutations that give the virus an advantage is the same process of evolution that people may remember from school, though it takes place on a microscopic level.

“Viruses mutate because that’s how evolution occurs,” he said.

Will the pace of mutation slow?

Rhoads sounded a somewhat hopeful note, saying in an e-mail, “Most other respiratory viruses including common coronaviruses are pretty stable genetically. My hypothesis is that this stability will also be achieved in SARS-CoV-2 eventually. However, the length of time to achieve this stability is unknown.”

Racaniello said, “I just don’t see it reaching any set point. It’s just going to keep going.” He pointed to the flu virus, which keeps mutating, requiring vaccinations every year.

At the same time, he said he felt people should not be panicking about news of Omicron or other vairants.

Scientists have raised alarms about the strikingly high number of mutations detected in the genome of the Omicron variant. Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle and a recent winner of a MacArthur “genius grant,” said in a virtual event held Tuesday that the number of mutations in the spike protein that allows the virus to penetrate cells is “kind of wild.”

“So other things that have been circulating — Alpha, Beta, Gamma, Delta, etc. —have maybe eight mutations, maybe 10, in spike protein. That’s largely what’s given them their advantageous phenotype. So Omicron ... it kind of comes out of nowhere, perhaps from an immunocompromised individual, and shows up with 30 mutations in the spike protein,” Bedford said.

“It looks striking. It looks worrisome,” he said, and “already seems like it will be functionally different.”

It will take about two weeks for more clarity to emerge on the potential danger posed by Omicron, experts say. Key questions include whether the virus is more transmissible, causes more severe illness, or evades vaccines.

“People should not be scared every time a new variant comes along,” Racaniello said. " ... The vaccines work and I think they’re going to continue to work as long as variants come out.” He said scientists’ ability to sequence the virus genome is a “double-edged sword,” providing important information and, at the same time, sowing alarm before the facts are in.

While solid information is still pending, some experts have noted that it’s possible that the numerous mutations will not work together to make the virus more fearsome, but instead will cancel each other out, in a phenomenon known as epistasis. “It is important to get a sense of the full virus,” Penny Moore, a virologist at the National Institute for Communicable Diseases in South Africa, told The New York Times.

Another theory that could raise people’s hopes is that viruses tend to evolve over time to become less virulent. The idea is that if the virus makes people less sick, it can be more successful in spreading to other people.

But the experts said that theory remains unproven. “The problem is we don’t have a lot of evidence for it,” Racaniello said.

Rhoads also said virus evolution could “go either way” in terms of illness severity because the illness people suffer is essentially “a side effect” of the infection.

So what is the key to stopping the mutations? Getting the world vaccinated, thus denying the virus a chance to keep trying to improve itself, experts say.

Dr. Anthony Fauci, the nation’s top infectious disease doctor, said at a briefing of the White House COVID-19 response team on Wednesday, “As we get more people vaccinated, not only here in this country but globally, we’ll see a situation where viruses will not have an opportunity, what they have right now, which is to essentially freely distribute and freely circulate in society, both domestic and global society.

“The more protections you get with vaccines, the less likelihood a virus has to do that, the less likelihood a virus has to mutate, the less likely you’re going to get a variant,” he said.

Racaniello said, “The more people vaccinated, the less virus evolution we’re going to see in people. ... We not only protect them from disease, we’re going to have fewer variants.”

He envisions a world perhaps a year or two from now when the pandemic has ended and there are only “little outbreaks” here and there.

“It depends on how long it takes before we can get the rest of the world vaccinated,” he said. “People just need to be vaccinated, and it will be all over.”

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Martin Finucane can be reached at martin.finucane@globe.com.

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2021-12-01 19:54:03Z
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