More Contagious Coronavirus Variant Found in Colorado

It’s the first confirmed U.S. case of the variant, which has overwhelmed hospitals in Britain.

A case of the more contagious coronavirus variant first discovered in Britain was found in Colorado on Tuesday, Gov. Jared Polis said. It is the first confirmed case of the variant in the United States.

The variant was detected in a man in his 20s with no travel history, Mr. Polis said. The man was in isolation in Elbert County, southeast of Denver, he said.

“There is a lot we don’t know about this new Covid-19 variant, but scientists in the United Kingdom are warning the world that it is significantly more contagious,” Mr. Polis said in a statement. “The health and safety of Coloradans is our top priority and we will closely monitor this case, as well as all Covid-19 indicators, very closely.”

Scientists are worried about these variants but not surprised by them. It is normal for viruses to mutate, and most of the mutations of the coronavirus have proved minor.

“This should not be cause for panic,” said William Hanage, an epidemiologist at Harvard University. “But it is cause to redouble our efforts at preventing the virus from getting the opportunity to spread.”

Earlier this month, British researchers observed that the variant was becoming more prevalent in parts of Britain. Their subsequent investigations suggest that the variant — known as B.1.1.7 — spreads more readily than others in circulation.

It’s not yet clear why B.1.1.7 transmits more easily. The lineage has accumulated 23 mutations since it split off from other coronaviruses. Researchers are investigating some of the mutations to see if they allow the viruses to invade cells more readily or make more copies of themselves.

There’s no evidence that an infection with B.1.1.7 is more likely to lead to a severe case of Covid-19 or increase the risk of death. But the speed at which the variant seems to spread could lead to more infections — and therefore more hospitalizations.

The British government has responded to the emergence of B.1.1.7 by enforcing stronger restrictions on people’s movements and the size of gatherings. In a preliminary study, British researchers found that schools may need to be closed and vaccination programs aggressively accelerated to prevent a huge surge in cases.

Countries around the world have implemented stricter protocols for travelers entering from the United Kingdom. A new rule in the United States mandating that incoming travelers from the U.K. — including American citizens — show proof of a negative coronavirus test upon entry went into effect on Monday.

It’s not clear where B.1.1.7 arose. The United Kingdom has the biggest system for sequencing the genomes of coronaviruses, which may be why the variant was first found there. Cases of the variant have also been identified in France, Spain and other European nations, as well as Lebanon and Singapore. Health officials in Ontario, Canada, said on Saturday that they had identified two cases of the variant in a couple with no known travel history or exposure.

Because the United States sequences far fewer genomes than Britain does, American scientists suspected that the variant might already have been in the country undetected. It appears they were right.

The fact that the Colorado man identified on Tuesday had no travel history raises the worrisome possibility that B.1.1.7 is already well established in his community — and perhaps elsewhere. “It didn’t teleport across the Atlantic,” Dr. Hanage said.

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