The United States will restrict travel from eight African countries—South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi—beginning Monday as the World Health Organization has classified a new coronavirus variant as a "variant of concern."

President Joe Biden, in his statement announcing the decision, urged Americans to get vaccinated or, if they are already vaccinated, get their booster shots.

"America is leading the world in vaccinating children ages 5-11, and has been vaccinating teens for many months now – but we need more Americans in all age groups to get this life-saving protection," he said. "If you have not gotten vaccinated, or have not taken your children to get vaccinated, now is the time."

According to the WHO, the first case of the new B.1.1.529 variant, which has been named after the Greek letter omicron, was found on November 9th in South Africa. After more cases emerged, the country reported the new variant to the global health agency on Wednesday.

The WHO said the variant "has a large number of mutations, some of which are concerning," and it is monitoring international studies to understand whether the variant may be more contagious. As of Friday, the WHO says omicron might increase the risk of reinfection, according to preliminary evidence. But it is unclear if the variant spreads quicker from person to person -- or if it can just replicate faster inside a body (outcompete) the delta variant. It is also unknown if the omicron variant can thwart vaccine-backed immunity. Thanks to one of its mutations, omicron can be easily detected with standard PCR tests.

The new variant's emergence has prompted the U.S. and other countries, including the United Kingdom and the European Union, to restrict travel from the southern African countries. That's despite a case of the new variant being identified in Belgium without any links to travel in those countries.

The report from Belgium's national reference laboratory stated, "The patient did not report any link with South Africa or other southern African countries. This patient had not previously been vaccinated and had not yet been infected. She developed flu-like symptoms, but does not present at this stage signs of severe disease."

On Twitter, Marc Van Ranst, a leading virologist in Belgium whose lab identified the case, added that the person had recently traveled to Egypt.

Belgian government officials announced some new restrictions, like the closure of nightclubs and banning private gatherings, but health minister Frank Vandenbroucke said, "I want to repeat that it is a suspect variant. We do not know if it is very dangerous. So: absolute precaution, but no panic pending further scientific analysis."

The New York Times reports, "[E]ven epidemiologists who have been the most outspoken in supporting precautions against the virus urged calm on Friday, noting that little is known about the variant and that several seemingly threatening variants have come and gone in recent months. 'Substantively NOTHING is known about the new variant,' Roberto Burioni, a leading Italian virologist, wrote on Twitter, adding that people should not panic."

"There’s no indication" that Omicron was present in the U.S., White House Chief Medical Advisor Dr. Anthony Fauci told CNN on Friday, before Biden announced the impending travel restrictions.

"Right now, we’re getting the material together with our South African colleagues to get a situation where you could actually directly test it," Fauci said. "So, right now, you’re talking about sort of like a red flag that this might be an issue – but we don’t know."

Further, the travel ban for the eight African countries will not apply to U.S. citizens or permanent residents. A negative COVID test is required before anyone travels to the U.S., but they can currently opt for a PCR or antigen test. The latter would not be able to pinpoint the omicron variant. The U.S. does not have mandatory quarantine periods after international travel or mandatory testing after arrival.

"While we have not yet identified any Omicron cases, we are not surprised that new variants are emerging and may likely end up in New York," New York Governor Kathy Hochul said in a statement Friday. "We will continue to monitor WHO actions and work with our partners at the CDC to keep a close eye on developments."

She also urged common sense COVID safety precautions and encouraged vaccinations.

"I want to remind New Yorkers to continue taking the precautionary steps we know reduce the spread of this deadly virus: wear a mask in indoor public places, use proper hand hygiene, get tested, and stay home when sick," she said. "The vaccine also remains one of our greatest weapons in fighting the pandemic, and this news further emphasizes the need for each of us to get vaccinated and get the booster if you're fully vaccinated."

Here's information from New York City, New York State, and New Jersey for getting vaccines. NYC also has an at-home vaccination program.