Researchers studying the new UK strain of the coronavirus think it likely arrived in the US in mid-November, and that many people in the United States could already be infected.

"If I had to guess, I would say it's probably in hundreds of people by now," said Michael Worobey, head of the department of ecology and evolutionary biology at the University of Arizona. "It's very possible it's arrived multiple times in multiple places."

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"Imagine the amount of infected travelers leaving London -- that's been increasing exponentially," said Trevor Bedford, associate professor in the vaccine and infectious disease division of the Fred Hutchinson Cancer Research Center.
British scientists have traced the new strain's earliest known appearance back to September 20 in Kent, a county southeast of London.
Worobey and Bedford say they estimate the virus would have arrived in the US in mid-November.
Both scientists, as well as others around the world, have scoured genetic sequences of coronavirus in the United States to see if any match up with the UK variant. So far, they haven't found any, but they say that's likely because the US surveillance system isn't catching them.

"You really need to assume that it's here already, and certainly is not the dominant strain, but I would not be surprised at all if it is already here," Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said Tuesday.

"It could be in the United States, and we might not have yet detected it," Assistant Secretary for Health Admiral Brett Giroir said Monday.
The UK coronavirus variant has not been identified through sequencing efforts in the United States, the US Centers for Disease Control and Prevention said in a scientific brief posted on its website Tuesday.However, it says, only about 51,000 of 17 million US cases it has tallied have been sequenced — less than half a percent.

"Given the small fraction of US infections that have been sequenced, the variant could already be in the United States without having been detected," the CDC said.
To detect new mutations of a virus, samples are gathered from infected patients and then undergo genetic sequencing, looking at the order of the letters in its genetic code for anything new.