Botswana confirmed on Thursday that a new COVID-19 variant, one that’s causing great concern in southern Africa and beyond, was detected in four people described as travelers.

Botswana’s Presidential COVID-19 Task Force said the four cases of the B.1.1.529 variant were recorded on Monday. All four cases happened in people who are vaccinated, the task force added.

“Initial investigations on the virus have established that the new variant has a high number of mutations as compared to the locally predominant Delta variant,” the statement said. “What this means is still unclear and under investigation.”

That investigation into some 30 mutations and their function is causing some real concern among scientists. They describe characteristics that suggest the variant is capable of spreading quickly and may not respond as well to existing COVID-19 vaccines. It’s a growing problem for South Africa, where the variant accounts for a number of recent cases.

“It is very clear from the data that various parts of Gauteng show a fast increase of infection,” said South African health minister Dr. Joe Phaahla. That includes Tshwane, Ekurhuleni, Sedibeng and West Rand.

The World Health Organization plans a special meeting Friday to discuss the B.1.1.529 variant and its impacts in Africa.

Meanwhile, the British government announced early Friday that all flights from South Africa, Namibia, Zimbabwe, Botswana, Lesotho and Eswatini are being suspended. The ban goes into effect at noon London time, the BBC reported.

UK Health Secretary Sajid Javid said his department is investigating the new variant.

“More data is needed but we’re taking precautions now,” said Javid. “From noon tomorrow, six African countries will be added to the red list, flights will be temporarily banned, and UK travelers must quarantine.”