US authorities are looking "very carefully" into the virus variant spreading in the United Kingdom, top health officials said Sunday, while indicating that a ban on UK travel was not currently in the cards.

The news came as a US expert panel recommended those aged 75 and older should be the next vaccinated against the virus, along with 30 million "frontline essential workers," including teachers, grocery store employees and police.

Addressing the virus variant, Moncef Slaoui, chief advisor to the government's Operation Warp Speed vaccine program, told CNN's "State of the Union" that US officials "don't know yet" if it is present in the country.

"We are, of course... looking very carefully into this," including at the National Institutes of Health and the US Centers for Disease Control and Prevention, he said.

At the moment, he said, no strain of the virus appears to be resistant to the vaccines available.

"This particular variant in the UK, I think, is very unlikely to have escaped the vaccine immunity," Slaoui said.

"I don't think there's any reason for alarm right now," agreed Admiral Brett Giroir, the US official overseeing coronavirus testing, when asked about the new variant on ABC's "The Week."

Asked whether the United States was likely to follow the example of European countries that have suspended flights from the United Kingdom, Giroir replied: "I really don't believe we need to do that yet."

Nearly eight million more Covid-19 vaccine doses are to ship across the United States on Monday, Slaoui told CNN -- two million of the Pfizer/BioNTech vaccine and 5.9 million of the Moderna shot that was greenlighted on Friday.

The first Moderna shot was "most likely to be tomorrow morning," he said.

- Outbreak may get worse -

The US Centers for Disease Control says 2.8 million vaccine doses were distributed over the past week, while 556,208 doses were administered.

While Vice President Mike Pence has done so publicly, and President-elect Joe Biden is to do so Monday, President Donald Trump has so far not indicated he will take the vaccine any time soon. 

With vaccine skepticism a concern, Giroir encouraged Trump to do so for his own health -- "and also to generate more confidence among the people who follow him so closely."

More than 316,000 people have been killed by Covid-19 in the United States, with new daily infections regularly topping 200,000 and deaths hovering at around 3,000 people every 24 hours.

With vaccines on the move there is light at the end of the tunnel -- but Slaoui warned the situation will "get worse" before it gets better, citing a surge after Thanksgiving and the coming year-end holidays.

Later in the day, a US Centers for Disease Control advisory panel voted to recommend which groups should be in the second wave of vaccinations after initial doses focused on frontline health-care workers and the elderly in nursing homes.

It recommended "frontline essential workers" along with those over the age of 75.

The panel estimates there are some 30 million people in the frontline essential workers category, ranging from teachers to postal workers, police and firefighters.

A following phase would see those between 65 and 74 years old along with other essential workers among those receiving doses, according to the recommendations.

The CDC will later decide whether to adopt the recommendations, while individual states can ultimately choose how to distribute their shots.