The primary United States case of the more contagious coronavirus variant that was initially found in Britain was present in Colorado on Tuesday, Gov. Jared Polis stated, elevating the worrisome risk that the variant is already properly established within the affected person’s neighborhood — and maybe elsewhere.

“It didn’t teleport throughout the Atlantic,” stated William Hanage, an epidemiologist on the Harvard T.H. Chan School of Public Health.

The variant was detected in a person in his 20s with no journey historical past, Mr. Polis stated. The person was in isolation in Elbert County, southeast of Denver, he stated.

Dr. Hanage stated the newly reported case “shouldn’t be trigger for panic.” However, he added, “it’s trigger to redouble our efforts at stopping the virus from getting the chance to unfold,” he stated.

Scientists are nervous about variants however not shocked by them. It’s regular for viruses to mutate, and a lot of the mutations of the coronavirus have proved minor. There’s no proof that an an infection with the variant — referred to as B.1.1.7 — is extra more likely to result in a extreme case of Covid-19, enhance the danger of demise or evade the brand new vaccines.

However the pace at which the variant appears to unfold may result in extra infections — and due to this fact extra hospitalizations.

The case recognized on Tuesday got here from Elbert County, Colo., which has a inhabitants of about 27,000. Colorado’s circumstances, deaths and hospitalizations have been steadily falling in latest weeks.

“There’s a lot we don’t learn about this new Covid-19 variant, however scientists in the UK are warning the world that it’s considerably extra contagious,” Mr. Polis stated. “The well being and security of Coloradans is our prime precedence, and we’ll carefully monitor this case, in addition to all Covid-19 indicators, very carefully.”

The Facilities for Illness Management and Prevention stated in an announcement on Tuesday that it anticipated “there will probably be extra circumstances which can be more likely to be detected within the coming days.”

It isn’t clear the place B.1.1.7 arose. Britain has the largest system for sequencing the genomes of coronaviruses, which can be why the variant was first discovered there.

Earlier this month, British researchers noticed that the variant was changing into extra prevalent in elements of Britain. Their subsequent investigations recommend that the variant spreads extra readily than others in circulation.

It additionally just isn’t but clear why B.1.1.7 transmits extra simply. The lineage has accrued 23 mutations because it cut up off from different coronaviruses. Researchers are investigating among the mutations to see if they permit the viruses to invade cells extra readily or make extra copies of themselves.

Prime Minister Boris Johnson first raised the alarm over the variant spreading in England on Dec. 19. He responded to the emergence of B.1.1.7 by imposing stronger restrictions on individuals’s actions and the scale of gatherings.

A lot of southern and japanese England, together with London, has been below the very best degree of restrictions. The principles require individuals to remain at residence aside from pressing journey, medical appointments and out of doors train. And the British Military was mobilized to assist the Nationwide Well being Service, the nation’s well being care system, arrange websites to manage speedy coronavirus checks to drivers, going truck to truck to conduct checks.

“When the virus adjustments its methodology of assault, we should change our methodology of protection,” Mr. Johnson stated on the time. “We now have to behave on data as we’ve it, as a result of that is now spreading very quick.”

Fears of the variant’s unfold from Britain final week led much of Europe to isolate the United Kingdom. As a part of that effort, France imposed a 48-hour blockade of the British border that created chaos on either side of the English Channel and warnings in Britain that some recent items may run brief for a quick time.

As of late final week, more than 50 governments had imposed restrictions.

A new rule in the United States mandating that vacationers arriving from Britain — together with Americans — present proof of a detrimental coronavirus take a look at upon entry was introduced late Thursday and went into impact Monday.

However consultants famous that the earliest British samples of B.1.1.7 dated again to September. It was doubtless that the variant had already unfold between nations.

It seems they have been proper. Instances of the variant have been recognized in additional than a dozen nations the world over. Well being officers in Ontario, Canada, said on Saturday that they’d recognized two circumstances of the variant in a pair with no recognized journey historical past or publicity.

The US sequences far fewer genomes than Britain does, which has led American scientists to suspect that the variant may have already got been within the nation undetected as properly. On Tuesday, the US joined the ranks of countries with B.1.1.7.

Dr. Hanage stated that the US must enhance the way it screens the genetic sequences of circulating viruses to trace their unfold. It’s conceivable that the brand new variant might need fueled latest outbreaks within the Midwest and Rhode Island, for instance, however scientists have no idea as a result of public well being officers haven’t been monitoring the viruses fastidiously sufficient throughout your entire nation.

“The US is hobbled by the inconsistency of its method,” he stated. “Until we activate the lights, we gained’t realize it’s there.”

As a result of B.1.1.7 seems to be a lot extra contagious than different strains, British researchers have warned that present restrictions in the UK will not be ample. In a preliminary study, they discovered that faculties might must be closed and vaccination packages aggressively accelerated to stop a surge in circumstances.

If B.1.1.7 takes off in the US, it’s doable that vaccination might should speed up there as properly. However within the first two weeks, the U.S. vaccination program is shifting more slowly than expected.

“You want to have the ability to get no matter obstacles to transmission you possibly can on the market as quickly as doable,” Dr. Hanage stated.

Nicholas Davies, an epidemiologist on the London Faculty of Hygiene and Tropical Medication, said in an interview last week that it was clear “that extra speedy vaccination goes to be a extremely necessary factor for any nation that has to take care of this or comparable variants.”