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The U.S. will ban travel from South Africa and several other African nations starting on Monday due to the emergence of the Omicron variant (B.1.1.529), which may have the ability to evade COVID vaccines and increase the risk of reinfection.

A statement from President Biden noted that he was briefed by his chief medical advisor, Anthony Fauci, MD, about the variant, and ordered the travel ban from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi. Politico reported that the president on the travel ban.

"As we move forward, we will continue to be guided by what the science and my medical team advises," Biden said.

CDC on Friday, saying that the agency is continuously monitoring variants and "we expect Omicron to be identified quickly, if it emerges in the U.S."

Fauci that there's no indication that Omicron is in the U.S. right now, but "it's possible." He also characterized its large number of mutations as a "red flag."

The variant "has some mutations that are raising some concerns, particularly with regards to possible transmissibility increase and possible evasion of immune response," he said. "We don't know that for sure right now, this is really something that's in motion."

Other countries, including the European Union, the U.K., and parts of Asia had already banned travel from South Africa.

The World Health Organization (WHO) also weighed that named B.1.1.529 a variant of concern (VOC) following a meeting of their Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE).

"This variant has a large number of mutations, some of which are concerning," the group wrote. "Preliminary evidence suggests an increased risk of reinfection with this variant, as compared to other VOCs."

South Africa first reported Omicron to the WHO on Wednesday, noting that "infections have increased steeply, coinciding with the detection of B.1.1.529 variant."

The variant was first detected in Botswana, but spread to South Africa, where it was first detected on November 9, the statement said. there are 87 confirmed cases worldwide. All but 10 of these cases are in South Africa -- six are in Botswana, two in Hong Kong and one apiece in Israel and Belgium.

A report from noted that Omicron contains more than 30 mutations to the spike protein, and these changes have been "linked to heightened infectivity and the ability to evade infection-blocking antibodies." In addition, all 77 virus samples from South Africa's Gauteng province from November 12 to 20 were B.1.1.529.

"My big concern is transmissibility, we've had other immune escape variants like beta and lambda which never took off. The key question: more or less transmissible and can it out compete delta?" Peter Hotez, MD, PhD, of Baylor College of Medicine.

Other unanswered questions noted by experts include the question of whether the variant causes more severe disease, which should be apparent as more data accrue.