Why new coronavirus variants 'suddenly arose' in the U.K. and South Africa

Some researchers suspect chronic cases allow the virus to replicate over long periods of time and that certain new therapies may encourage it to mutate.

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Pedestrians walk along the Riv​er Thames in London, October 18, ​2020.

In early December, cases of COVID-19 soared in Kent, England—and scientists wanted to know why. For clues, Nick Loman, who is part of the COVID-19 Genomics Consortium U.K., and his colleagues examined how the coronavirus was mutating. By looking at this zoo of slightly different viruses, they could roughly track the outbreak’s spread through the community.

For SARS-CoV-2, these mutations—the small errors made naturally when genomes are copied—develop at a steady pace of one or two each month, says Loman, a professor of microbial genomics and bioinformatics at the University of Birmingham. Yet among the Kent cases, scientists found a large cluster that was remarkably different, with a total of 23 mutations arising without prior notice and faster than anyone expected.

"That's how many mutations you have to go back to get to anything we'd seen before," he says. "That's a very striking and unusual finding."

This discovery is part of what led British officials to sound the alarm last week. A follow-up investigation by Public Health England showed that the variant, known as B.1.1.7 or 501Y.V1, began to thrive at a time when cases were spiking in Kent and other parts of southeastern England. Retroactive tracing through a database of samples tied B.1.1.7 to patients as early as September 20. But by mid-November, the variant made up between 20 and 30 percent of cases in London and a region east of the city. Three weeks later, it was roughly 60 percent. And on December 23, U.K. scientists announced a...

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