(Bloomberg) -- U.K. authorities will temporarily ban flights from six African countries and place travelers into quarantine over worries about a new, dramatically different Covid-19 variant recently identified there. 

The travel restrictions go into effect at noon Friday and are a precautionary measure to keep the spread of the new variant in check, Health Secretary Sajid Javid said. The six countries will be placed on the U.K.’s red list, which requires travelers to quarantine in hotels upon arrival in the U.K.

Scientists are still trying to determine whether the new variant, called B.1.1529, is more transmissible and more lethal than the versions of the virus that have dominated the pandemic thus far. Health authorities will also screen travelers who have recently landed from South Africa, where the new variant has been spreading.

What’s already clear is that the new variant has the most mutations of any yet identified and that it’s very different from previous incarnations of the virus. That’s raised concerns both inside South Africa and internationally, with authorities fearing a wave of cases that could increase the pressure on already strained health-care systems. 

In South Africa, virologists have detected almost 100 cases linked to the variant to date, according to Anne von Gottberg, a clinical microbiologist and head of respiratory diseases at the National Institute for Communicable Diseases. World Health Organization officials have met to discuss the variant, which has also been detected in Botswana, where it’s been found in people who were vaccinated against Covid.

“Armed by our experience and understanding of the alpha and delta variants, we know that early action is far better than late action,” Ewan Birney, deputy director general of the European Molecular Biology Laboratory, said in a Science Media Centre briefing note. “It may turn out that this variant is not as large a threat as alpha and delta, but the potential consequences of not acting on the possibility it could be are serious.” 

The new variant probably evolved during a chronic infection of an immuno-compromised person, possibly in an untreated HIV/AIDS patient, said Francois Balloux, director of the UCL Genetics Institute. The world’s biggest number of HIV cases has made it more difficult for South Africa to fight the Covid pandemic, because the virus can linger for longer in people whose immune systems are compromised, potentially offering a bigger window for mutations. 

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