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(CNN) — Pfizer and Moderna are testing their coronavirus vaccines to see if they work against the new mutated version of the virus that’s recently been found in the United Kingdom and other countries, according to company statements.

“Based on the data to date, we expect that the Moderna vaccine-induced immunity would be protective against the variants recently described in the UK; we will be performing additional tests in the coming weeks to confirm this expectation,” according to the Moderna statement.

Pfizer said it is now “generating data” on how well blood samples from people immunized with its vaccine “may be able to neutralize the new strain from the UK.”

The novel coronavirus has mutated before, and both companies say they’ve found that their vaccines worked against other variations of the virus.

The statements from the two companies reflect the increasing global concern about a new variant of the novel coronavirus that has rapidly spread through the UK.

Experts are unsure of the importance of this mutation, yet a number of countries, including Canada, have imposed restrictions on travelers from the UK.

The United States has not done so, but the White House is considering requiring travelers from the UK to present proof of a negative coronavirus test before arriving in the US, two administration officials told CNN on Monday.

US Surgeon General Jerome Adams said the UK variant “doesn’t change what we need to do” in regards to staying protected.

“What’s important for people to understand as this doesn’t change what we need to do,” he said. “We need to wear masks, wash hands, watch our distances and wait on gatherings, and we need to get vaccines, get vaccinated when those become available to us.”

Variant or not, the US has failed to limit the spread of Covid-19 as is. The winter solstice on Monday marked the darkest day of the year and provided a tidy metaphor for this period of the pandemic. The US reported about 191,000 new Covid-19 cases and 1,700 new deaths on Monday as more than 115,000 people were hospitalized with the virus, a record high.

The outbreaks are also not confined to any one region, as in earlier in the pandemic. Adjusted for population, the states with the most new cases over the past week are Tennessee, California and Rhode Island, according to data from Johns Hopkins University.

Yet just as the days are set to get longer and spring’s renewal nears, so too is the promise of widespread vaccinations. More than 614,000 doses of the vaccine have been administered, according to the US Centers for Disease Control and Prevention, and tens of millions more are expected in the coming months.

Dr. Anthony Fauci, the director of the National Institutes of Allergy and Infectious Diseases, said Monday that the UK coronavirus variant is probably already in the US.

“You have to make that assumption,” Fauci told PBS Newshour’s Judy Woodruff on Monday.

“When you see something that is pretty prevalent in a place like the UK, there are also mutations that we’re seeing in South Africa, and given the travel throughout the world, I would not be surprised if it’s already here.”

“Certainly it’s not yet the prevalent one, the way it seems to have assumed that prevalent nature in the UK, but we’re going to be looking for it right now, and I’m sure sooner or later we’re going to run into it and find it,” he added.

Mutations in the virus are not out of the ordinary, and most have no noticeable impact, Fauci said. Researchers are still trying to determine if the UK variant is more transmissible, but Fauci said said it doesn’t seem to have any impact on the deadliness of the virus.

Fauci said he thinks a UK travel ban is premature because there’s not enough evidence to warrant it. He said he prefers considering the possibility of mandatory testing of travelers from the UK.

Some researchers who are examining the genome of the UK variant told CNN they have concerns that this variant’s mutations might somewhat diminish the effectiveness of the vaccine.

“You could imagine some modest hit in vaccine efficacy, which wouldn’t be good, but I don’t think it would break the vaccine,” said Trevor Bedford, an associate professor in the vaccine and infectious disease division of the Fred Hutchinson Cancer Research Center.

Other experts, though, have been skeptical of any impact on the vaccines.

“It doesn’t make people more sick and it doesn’t seem to have any impact on the protective nature of the vaccine that we’re currently using,” Fauci said.

Moncef Slaoui, chief scientific adviser for Operation Warp Speed, said during a news briefing Monday that there is no “hard evidence” that the variant is more transmissible.

“There is clear evidence that there is more of it in the population,” he said. “Whether it’s due to a higher capacity to transmit or whether it’s due to the fact that we now are able to sequence all the time and see the virus, while when it was seeding the population in the southeast of the UK, we were not, or they were not, looking for this particular variant.”

The CEO of BioNTech, which collaborated with Pfizer on their vaccine, said he has “scientific confidence” that the current Pfizer-BioNTech vaccine could work against the new variant, but full data will be available in two weeks.

“We don’t know at the moment if our vaccine is also able to provide protection against this new variant, but scientifically it is highly likely that the immune response by this vaccine also can deal with the new virus variant,” Ugur Sahin said at a press conference Tuesday.

“We have scientific confidence that the vaccine might protect, but we don’t know it, only if the experiment is done and we will need about two weeks from now to get the data.”

Over 600,000 vaccines administered

In just over a week since US vaccinations began, more than 4.6 million vaccine doses have been delivered and about 614,000 doses have been administered, according to the CDC.

The first round of doses have been given to those in assisted living facilities, federal officials and health care workers like Dr. Joseph Varon.

Varon, critical care doctor and chief of staff at United Memorial Medical Center in Houston, was one of the first people to get a dose of the Moderna vaccine, which the FDA authorized for emergency use on Friday.

“This is like having gold,” Dr. Joseph Varon told CNN on Monday, as he held a box of doses. “I don’t cry, but I came very close … You know how many lives you can save with this?”

Both Moderna’s and Pfizer’s vaccines were shown to have about 95% efficacy in clinical trials and have minimal differences for the person receiving the shot.

The first doses of Moderna’s vaccine were sent to more than 3,500 sites across the US, compared to over 600 sites for Pfizer’s. In all, 7.9 million doses from Moderna and Pfizer will be distributed this week in the US, Operation Warp Speed’s Gen. Gustave Perna said Monday.

One of the people distributing the vaccine is Todd Elble, a UPS tractor trailer driver whose father died from Covid-19.

“I know my dad is smiling down on us right now,” he said.