Global authorities reacted with alarm on Friday to a new coronavirus variant detected in South Africa, with the EU and Britain among those tightening border controls as researchers sought to find out if the mutation was vaccine-resistant.

Hours after Britain banned flights from South Africa and neighbouring countries and asked travellers returning from there to quarantine, the World Health Organisation (WHO) cautioned against hasty measures.

One South African scientist expert labelled London’s decision a symptom of “vaccine apartheid”, though European Commission chief Ursula von der Leyen said the EU also aimed to halt air travel from the region and several other countries including India, Japan and Israel toughened curbs.

Read more: Asian and European countries, alarmed by new Covid variant, tighten curbs

In Washington, top US infectious disease official Anthony Fauci said no decision had been made on a possible US travel ban.

There was no indication that the variant was in the United States, and it was unclear whether it was resistant to current vaccines, he told CNN.

The WHO said it would take weeks to determine how effective vaccines were against the variant, which was first identified this week, but the news pummelled global stocks and oil amid fears what new bans would do to the global travel industry and already shaky economies across southern Africa.

The variant has a spike protein that is dramatically different to the one in the original coronavirus that vaccines are based on, the UK Health Security Agency said, raising fears about how current vaccines will fare.

“As scientists have described, (this is) the most significant variant they’ve encountered to date,” British Transport Secretary Grant Shapps told Sky News.