The US will restrict travel from South Africa and seven other countries starting on Monday. The move comes amid fears that a new COVID variant discovered in South Africa may be more transmissible and vaccine-resistant than the delta variant.

President Joe Biden was briefed on Friday by Dr. Anthony Fauci, his chief medial adviser, and other members of the COVID response team about the variant. The new variant had already led Israel, Singapore and several European nations, including Britain, to block travel to southern Africa.

«As a precautionary measure until we have more information, I am ordering additional air travel restrictions from South Africa and seven other countries,» said Biden in a statement. «As we move forward, we will continue to be guided by what the science and my medical team advises.»

The US air travel restrictions will apply to travelers from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi. It’s unclear how long the restrictions will be in place.

The variant, which was given the name omicron by the World Health Organization on Friday, was first identified as B.1.1.529 in South Africa on Tuesday. Scientists are concerned about it because of its high number of mutations. Their worry is that vaccines designed to target previous COVID-19 variants may be less effective.

The WHO acknowledged in a Friday release that the variant was «concerning» and noted that preliminary evidence «suggests an increased risk of reinfection with this variant.»

There were 22 known cases of omicron as of Thursday, according to South Africa’s National Institute for Communicable Diseases. It’s also been detected in Botswana, South Africa’s neighbor to the north, as well as Israel, Belgium and Hong Kong, which are thousands of miles away.

«This variant did surprise us,» Tulio de Oliveira, director of the KwaZulu-Natal Research and Innovation Sequencing Platform, said in a press conference on Thursday. «It has a big jump in evolution, many more mutations than we expected, especially after a very severe third wave of delta.»

US stocks tumbled Friday on the news of the variant, CNBC reported.

A ‘variant of concern’

In the nearly two years since the first outbreaks of the disease, there have been more than 260 million cases of COVID-19 reported worldwide, resulting in more than 5.1 million deaths, according to the Johns Hopkins University COVID-19 dashboard. Vaccines from Pfizer-BioNTech, Moderna and Johnson & Johnson have proved highly effective in restraining the spread of the coronavirus that causes COVID-19 and in easing the effects for those who contract it. But vaccination rates vary widely around the globe and in individual nations.

Whether the mutations of Omicronwill translate to a more dangerous, transmissible and vaccine-resistant form of COVID-19 is as yet unknown. COVID-19 constantly mutates, and many of those mutations don’t substantially affect the virus.

«We don’t know very much about this yet,» Maria Van Kerkhove, the WHO’s technical lead of COVID, said in a livestream on Thursday. «What we do know is that this variant has a large number of mutations. And the concern is that when you have so many mutations, it can have an impact on how the virus behaves.»

«It will take a few weeks for us to understand what impact this variant will have.»

On Thursday, UK Secretary for State Health Sajid Javid announced that South Africa and five other southern African countries — Namibia, Zimbabwe, Botswana, Lesotho and Eswatini — would be added to the UK’s travel red list. Flights to those countries are being stopped, while travelers returning to the UK from those countries will have to quarantine.

Singapore, Italy, France and Israel have also placed Mozambique on their red lists, The New York Times noted. Dubai said it’ll restrict entrance to travelers from those countries starting Monday.

Ursula von der Leyen, president of the European Union’s executive arm, tweeted Friday that her commission would also propose restricting air travel to European countries from southern Africa.

The vaccine co-developed by Pfizer and BioNTech is the most widely administered in the US, according to CDC data, and a BioNTech spokesperson told Reuters it’ll quickly be able to determine how effective the vaccine is against the variant.

«We expect more data from the laboratory tests in two weeks at the latest. These data will provide more information about whether B.1.1.529 could be an escape variant that may require an adjustment of our vaccine if the variant spreads globally,» the spokesperson said Friday. An escape variant would resist the targeted immune response caused by vaccination.

That a new variant has emerged in Africa comes as little surprise to many epidemiologists. Viruses, like the one that causes COVID, mutate during replication. In places with low vaccinations and high case numbers, new variants are more likely to arise, as in the case of delta’s emergence from India. African countries have low vaccination rates, and huge parts of the population are too poor to miss work via shelter-in-place orders or to seek medical help. South Africa is the richest country in Africa, yet only has a double vaccination rate of around 23%.

On Friday, Biden said the emergence of the omicron variant underscores the need for «global vaccinations» to end the pandemic. He urged officials attending a World Trade Organization meeting next week to waive intellectual property protections for COVID vaccines, a position the president endorsed earlier this year.

CNET’s Carrie Mihalcik contributed to this report.