(CNN) — 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.”
“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.
Health officials agree.
“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.
In the US, only a relatively small number of samples go through this process.
Since November 15 — about the time the UK variant might have arrived in the US — genetic sequencing has been done on viruses found in about 300 people in the United States and in about 9,000 in the UK, Worobey said.
“We’re flying blind,” Worobey said. “Maybe some other similarly interesting variant is sweeping up with high frequency, but we’re just not seeing it.”
On its website, the CDC notes that of about 275,000 full-genome sequences in public databases, 51,000 are from the United States, and 125,000 are from the UK.
This difference is especially striking considering how many more infections have been confirmed in the US — over 18 million – compared with over 2.1 million in the UK.
Health officials say research so far shows the changes do appear to make the virus more transmissible, but it doesn’t appear that the variant causes more severe disease. They also say that at this point, it looks like the vaccine will still work against the UK variant.
Last month, the CDC launched a strain surveillance program where states will send in at least 10 samples biweekly for analysis. The agency expects to have the program fully implemented in January.
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