At least two states as of Wednesday had confirmed cases of a fast-spreading new variant of the coronavirus less than two weeks after it was first detected in the United Kingdom. The mutation, which prompted countries across Europe to halt travel from Britain in mid-December, now adds to concerns mounting stateside that a more-infectious variant of the virus will crush the capacity of hospitals already on the brink.

The defining characteristic of the British variant, known as B.1.1.7., appears to be its transmissibility; it reportedly accounted for more than half of all recent infections in London, according to the Centers for Disease Control and Prevention.

Viruses change every time they replicate themselves, which is normal and usually means nothing, said Cathy McCarty, associate dean of research at the University of Minnesota Medical School at Duluth. The U.K. mutation appears to have changed the virus’s spike protein enough to where the variant becomes more infectious and “sticks” to people more easily, like a burr, she said.

“It’s probably at least 50 percent more infectious as the version that’s been around,” McCarty told The Washington Post on Wednesday. “The good news is that it does not appear that patients who get infected [with the variant] are any more likely to die, be hospitalized or get reinfected.”

Variations to the virus are nothing new, and experts say the novel coronavirus does not mutate as much as influenza, meaning it is less likely that a vaccine would need to be developed every year to keep up with new strains.

With only a fraction of the U.S. population vaccinated thus far — roughly 2.5 million people — researchers don’t have enough data to determine whether the current vaccines are less effective against the U.K. variant of the virus.

McCarty noted that data on the variant is still scant and that the understanding of its infectiousness or lethality could change as more information emerges.

“The take-home message for right now is that we need to get more information,” said Krutika Kuppalli, an infectious-diseases specialist at the Medical University of South Carolina. “In the meantime, we all need to really double down on our public-health measures — wearing masks, remaining physically distanced, avoiding crowds of people.”

Where has the variant been detected?

On Wednesday, California became the second state after Colorado to confirm U.S.-based cases of the variant. At least 19 other countries have identified cases of the U.K. variant, including Australia, Finland, France, Denmark, Singapore and South Korea — but the total number of countries where it may have spread is unknown.

In December, British researchers first discovered the variant’s prevalence when they collected samples from infected people in southeastern England. It seemed to spread quickly.

“This lineage came up quite rapidly,” Nick Loman, one of the researchers and a professor of microbial genomics at the University of Birmingham, previously told The Washington Post.

In South Africa, health officials said Sunday that a version of the virus similar to the U.K. variant has been found in 80 to 90 percent of samples analyzed since mid-November; the South African variant has not been confirmed in the United States.

British Prime Minister Boris Johnson said Dec. 19, "We cannot continue with Christmas as planned," due to findings on a new mutation of the novel coronavirus. (Reuters)

How long has the variant been in the United States?

The virus variant was first detected in the United States on Tuesday from a case in Colorado involving a man in his 20s, but it’s unclear exactly when the variant arrived on U.S. shores.

On Christmas Day, the Centers for Disease Control and Prevention signed an order requiring American citizens and others flying from Britain to test negative for the coronavirus before boarding a U.S.-bound flight.

By Wednesday, a second suspected infection involving the variant emerged in Colorado, while a third case was identified in California.

Unlike many patients in southern England, where the variant first emerged, in all three U.S. cases, none of the patients are believed to have traveled recently. That, researchers say, suggests the variant is already circulating in some communities in the United States.

Does the variant manifest different symptoms?

The U.K. variant does not appear to produce different or more severe symptoms than the version of the novel coronavirus (officially known as SARS-CoV-2) that has been in the United States all year.

Patients infected with the U.K. variant won’t be able to tell based on their symptoms alone, said McCarty, the University of Minnesota researcher. To find out what variant of the virus a patient has, the hospital or a lab will have to perform molecular testing.

“We expect we’ll see an increase in the number of cases, with people getting together for the holidays,” McCarty said. As for the variant, it’s “here, and it’s been here,” she said.

“Because we haven’t had a lot of molecular testing, it’s going to be hard to tease out what [the case increase is] due to — or if it’s due to both,” McCarty said.

Will the authorized vaccines still be effective against this variant of the virus?

As of now, experts say there has been no indication that the variant is resistant to the Pfizer and Moderna vaccines authorized by the Food and Drug Administration.

“The way the vaccines work is they act on our body’s reaction to the spike protein,” which is the part of the virus that has mutated, McCarty explained. “Experts are hoping this variant will not impact resistance to the vaccine, but we just don’t know.”

Although the vaccine remains out of reach for most Americans, following guidance such as social distancing and wearing masks remains the most practical way to prevent transmission.