Countries across Europe halted air travel from southern Africa amid growing concern about a new, potentially riskier Covid-19 variant that originated there and has since been traced in people from Belgium to Israel.

The emergence of the mutation prompted a rapid response by governments. European Commission President Ursula Von der Leyen proposed to activate an emergency ban for air travel from southern Africa until there’s a clearer understanding of the potential dangers. The U.K. followed suit, though no cases of the new variant have yet been detected in the country.

Belgium, on the other hand, confirmed one case of the new Covid-19 variant, called B.1.1529, in someone who traveled from abroad. In Israel, an individual arriving from Malawi was also found to carry the new strain, prompting Prime Minister Naftali Bennett to say his country was “on the verge of an emergency situation.”

The new threat comes just as the latest wave of infections spirals out of control in countries from Germany to Belgium to Austria. Some parts of Europe are already back in lockdown due to a spike in cases. In the U.K., which has effectively abandoned restrictions such as mask-wearing and other social-distancing measures, Health Secretary Sajid Javid said the new variant poses “substantial risk” to public health, though government has no plans yet to upgrade pandemic rules.

The European Centre for Disease Prevention and Control assigned the strain the category “Variant of Concern.”

The tightening of travel rules are a fresh blow to the airline industry, which was just starting to recover from earlier travel restrictions. European stocks slumped on Friday, heading for their sharpest drop this year, tracking Asian stocks lower. Energy, banks and air transport led declines, with Deutsche Lufthansa AG and IAG SA, the owner of British Airways, plunging.

Scientists are still trying to determine whether the new variant is more transmissible or more lethal than previous ones, but it does have the most mutations of any strain yet identified. That’s raised concerns inside South Africa and internationally, with authorities fearing a wave of cases that could increase pressure on already strained health-care systems.

Susan Hopkins, chief medical adviser to the U.K. Health Security Agency, told BBC radio the variant has about 30 mutations “that seem relevant”—double the number seen in the highly-transmissible delta variant.

German biotech company BioNTech SE, which has developed one of the most widely used Covid-19 vaccines with Pfizer Inc., has begun studying the new variant and expects the first data from laboratory tests about how it interacts with its vaccine within two weeks.

Speaking in Brussels, von der Leyen said EU contracts with vaccine manufacturers require companies to adapt the medication to new variants when necessary as they emerge.

Crossroads

German Health Minister Jens Spahn said that starting Friday night only German citizens will be allowed to fly back from South Africa, and anyone arriving from there will have to go into quarantine for 14 days, even if they’re vaccinated.

Europe’s largest economy is already grappling with resurgent virus cases, which have repeatedly hit records this month. That’s prompted health officials to demand stricter curbs on contacts. Spahn himself hasn’t ruled out another lockdown, following Austria’s example, which enacted strict curbs a few days ago.

“We’re standing at a crossroads,” said Lothar Wieler, president of Germany’s Robert Koch Institute. “We have a choice. We can take the path that ends in chaos and disaster,” or hope for a “peaceful Christmas” if people make different choices.

The moves on travel restrictions come one day after the EU revised its rules to facilitate and harmonize travel within and into the bloc.

Italy and the Netherlands also said they would restrict travel from the region, as did Israel after the discovery of the infected man returning from Malawi.

The U.K.’s travel restrictions WENT into effect Friday, banning flights from six African countries—South Africa, Botswana, Eswatini, Lesotho, Namibia and Zimbabwe—until Sunday. Arrivals after that must quarantine in a hotel.

South Africa criticized the U.K. move to ban flights, saying it was taken too hastily.

“Whilst South Africa respects the right of all countries to take the necessary precautionary measures to protect their citizens, the U.K.’s decision to temporarily ban South Africans from entering the U.K. seems to have been rushed as even the World Health Organization is yet to advise on the next steps,” Foreign Minister Naledi Pandor said in a statement on Friday.

But Devi Sridhar, a professor of global public health at the University of Edinburgh in Scotland, said governments don’t want to take risks now and are “not going to watch and wait like we’ve done in the past.”

In South Africa, virologists have detected almost 100 cases linked to the new variant to date, according to Anne von Gottberg, a clinical microbiologist and head of respiratory diseases at the National Institute for Communicable Diseases. No cases have been identified in the U.K., the health department said.

It will take weeks to understand the full impact of the variant, World Health Organization spokesman Christian Lindmeier said Friday. An expert panel is meeting today at the WHO to decide whether the strain is a variant of concern.