DENVER — The new and seemingly more contagious variant of the coronavirus that has set off alarm in Britain has been reported for the first time in the U.S., in a Colorado man who hadn’t been traveling, triggering a host of questions about how it got here and adding urgency to the nation’s vaccination drive.

The patient, a man in his 20s from a mostly rural expanse on the edge of the metropolitan Denver area, was recovering in isolation, state officials said Tuesday. His condition was not disclosed.

The new, mutated version was first identified in Britain, where infections are soaring and the number of hospitalized COVID-19 patients has surpassed the first peak seen last spring. The variant has also been found in several other countries.

“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,” Colorado Gov. Jared Polis said. “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.”

The variant is probably still rare in the U.S., but the lack of travel history in the first case means it is spreading, perhaps seeded by visitors from Britain in November or December, said scientist Trevor Bedford, who studies the spread of COVID-19 at the Fred Hutchinson Cancer Research Center in Seattle.

“Now I’m worried there will be another spring wave due to the variant,” Bedford said. “It’s a race with the vaccine, but now the virus has just gotten a little bit faster.”

Colorado Politics reported a second suspected case in the state. Both patients were working in the Elbert County community of Simla. Neither is a resident of the county, suggesting the variant has spread in the state.

Scientists in Britain Have Found No Evidence That It Is More Lethal or Causes More Severe Illness

Public health officials are investigating other potential cases of the variant, which was confirmed by the Colorado State Laboratory, and performing contact tracing to determine its spread.

Scientists in Britain have found no evidence that it is more lethal or causes more severe illness, and they believe the vaccines now being dispensed will be effective against it. Still, authorities have blamed it for the country’s spike in hospitalizations.

The discovery of the variant overseas led the U.S. Centers for Disease Control and Prevention to issue rules on Christmas Day requiring travelers arriving from Britain to show proof of a negative COVID-19 test.

British Prime Minister Boris Johnson reported the weekend before Christmas that the variant was moving rapidly through London and southeast England. The region was placed under strict lockdown measures, and dozens of countries banned flights from Britain. France also briefly barred trucks from Britain before allowing them in provided the drivers got tested for the virus.

Japan announced Monday it would bar all nonresident foreigners as a precaution.

New versions of the virus have been seen almost since it was first detected in China a year ago. It is common for viruses to undergo minor changes as they reproduce and move through a population. The fear is that mutations will become significant enough to defeat the vaccines.

South Africa has also discovered a highly contagious COVID-19 variant that is driving the country’s latest spike of cases, hospitalizations and deaths.