A notice informing people of 'Tier 4' coronavirus restrictions lights up a digital advertising screen on Oxford Street in London, England, on December 21, 2020.

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The U.K. has identified a new variant of the coronavirus that appears to spread more quickly, sparking fresh fears that the Covid-19 pandemic may continue to accelerate even as governments begin administering the first vaccine shots.

Scientists and infectious disease experts are still piecing together what they know about the new strain, called SARS-CoV-2 VUI 202012/01, which is shorthand for the first variant under investigation in December 2020, according to the Centers for Disease Control and Prevention. It hasn't yet been detected in the U.S., but the CDC said it could already be circulating across the country unnoticed.

While the virus appears to transmit more easily, there is "no evidence" that the new variant makes people sicker or increases the risk of death, the CDC said Tuesday. The new coronavirus "mutates regularly," the CDC noted, but the overwhelming majority of mutations are insignificant.

More than 40 countries, not including the U.S., have now suspended transport links with the U.K. after the new variation of the coronavirus was found.France activated a 48-hour border closure Monday, and by Tuesday morning 1,500 trucks were stuck in Kent, unable to leave the U.K., British Home Secretary Priti Patel said Tuesday.

Here's what you need to know:

The World Health Organization said the mutation was found in 1,108 cases in the U.K. as of Dec. 13. However, that's likely an undercount since scientists need to run additional tests to confirm which strain of the virus a patient is infected with, including sequencing the genetic code.

The WHO said the variant was traced back to the county of Kent in southeast England where it was found on Sept. 20, based on a retrospective analysis.

It wasn't until October, though, that the variant began to spread rapidly throughout the region, the WHO said, adding that cases continued to rise at an unexpected pace through November, prompting an investigation and discovery of the mutation earlier this month. Between Oct. 5 and Dec. 13, more than 50% of the viral samples from southeast England that were sequenced were found to be the variant strain.

The U.K. has said the variant could be up to 70% more transmissible than the original strain of the virus.

Based on early data from the U.K., the new strain could "potentially be more rapidly transmissible than other circulating strains," the CDC said.

Maria Van Kerkhove, head of the WHO's emerging diseases and zoonosis unit, said Monday that U.K. officials estimate that the mutation has caused an increase in the reproductive rate of the virus from 1.1 to 1.5. That means that each person infected with the variant is estimated to infect another 1.5 people.

Dr. Mike Ryan, executive director of the WHO's health emergencies program,said it was unclear if the increase in spread in the U.K. is because of the mutation or human behavior.

"We've seen an estimate of a small increase in the reproductive number by the U.K.," he said, meaning the virus is spreading faster, which could mean it is more contagious or spreads more easily in colder months. It could also mean people are getting lax about following public health protocols. "It remains to be seen how much of that is due to the specific genetic change in the new variant. I suspect some."

Officials in the U.K. are conducting epidemiological and virological investigations to determine whether the variant is more infectious, whether it causes people to become more sick, whether it can re-infect people who previously had Covid-19 and what kind of antibody response the new variant prompts.

The U.K. is also conducting genomic surveillance to understand the scope of spread of the new variant across the country. The U.K. has also placed affected areas under tier 4 restrictions, the strongest Covid rules in the country.

In the U.S., "viruses have only been sequenced from about 51,000 of the 17 million US cases," so the new strain could have slipped notice, according to the CDC.

The CDC launched a new program in November, the National SARS-CoV-2 Strain Surveillance program, to sequence more virus samples. It's supposed to be fully running in January where each state in the U.S. will send the CDC at least 10 samples every other week for sequencing and further study.

The WHO says laboratory studies are ongoing to determine whether the new virus has different biological properties or could alter vaccine efficacy. The mutations include changes to the spike protein that the virus uses to infect human cells.

Both Pfizer's and Moderna's vaccines, which have been authorized for use in the U.S. use messenger RNA, or mRNA, technology. It's a new approach to vaccines that uses genetic material in this case, a harmless piece of spike protein to provoke an immune response against the virus.

BioNTech CEO Ugur Sahin said Tuesday that he is confident the company's coronavirus vaccine with Pfizer will work against the new strain, but added but further studies are needed to be completely sure.

President Donald Trump's coronavirus vaccine czar, Dr. Moncef Slaoui, also said he expects Pfizer's and Moderna's Covid-19 shots will be effective against the new mutation.

Both vaccines induce an immune response against several structures found around the spike protein, the multifunctional mechanism that allows the virus to enter the host, Slaoui, chief science advisor to Operation Warp Speed, explained to reporters Monday during a press briefing. The chances one set of mutations would completely alter those structures "are extremely low," he added.

The CDC said Tuesday the new strain could already be circulating in the United States without notice.

"Ongoing travel between the United Kingdom and the United States, as well as the high prevalence of this variant among current UK infections, increase the likelihood of importation," CDC said in a statement. "Given the small fraction of US infections that have been sequenced, the variant could already be in the United States without having been detected."

The Associated Press contributed to this report.

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