“If I had to guess, I would say it’s probably hundreds of people by now,” said Michael Worobey, chief of the department of ecology and evolutionary biology at the University of Arizona. “It is quite possible that he arrived several times in several places.”
“Imagine the number of infected travelers leaving London – it’s gone up exponentially,” said Trevor Bedford, associate professor in the vaccines and infectious diseases division of the Fred Hutchinson Cancer Research Center.
British scientists have traced the earliest known appearance of the new species back to September 20 in Kent, a county south-east 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 searched genetic sequences of coronavirus in the United States to see if they match the British variant. So far, they haven’t found any, but they say that’s probably because the US surveillance system isn’t catching them.
Health officials agree.
“You really have to assume it’s already there, and certainly not the dominant strain, but I wouldn’t be at all surprised if it’s there,” says 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 may not have discovered it yet,” Deputy Secretary of 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 letter posted on their website Tuesday.
However, it says that only about 51,000 of the 17 million US cases it counted have been sequenced – less than half a percent.
“Given the small fraction of sequenced US infections, the variant could already be in the United States without being detected,” the CDC said.
To detect new mutations of a virus, samples are collected from infected patients and then undergo genetic sequencing, looking at the order of the letters in the genetic code for something new.
In the US, only a relatively small number of samples go through this process.
Since November 15 – about the time the British variant may have arrived in the US – genetic sequencing has been done on viruses found in about 300 people in the United States and about 9,000 in the UK, Worobey said.
“We’re flying blind,” said Worobey. “Maybe another similarly interesting variant is sweeping at a high frequency, but we just don’t see it.”
This difference is especially striking when you consider how many more infections have been confirmed in the US – over 18 million – compared to more than 2.1 million in the UK.
Last month, the CDC launched a pedigree surveillance program in which states send at least 10 samples every two weeks for analysis. The agency expects the program to be fully implemented by January.
CNN’s Michael Nedelman contributed to this report.