Authorities around the world reacted with alarm to a new coronavirus variant detected in South Africa, as researchers worked to establish if the mutation can resist vaccines.

On Friday, the last passengers arrived at London¢¥s Heathrow Airport from South Africa after Britain and other countries stopped flights from there and five neighboring countries. The new coronavirus variant alarmed scientists and world leaders because it has a spike protein that is dramatically different from the original virus that the vaccines are based on.

Belgium reported the first known case in Europe, adding to those in Israel, Botswana, and Hong Kong. The World Health Organization cautioned against hasty travel bans; however, the European Commission Chief Ursula von der Leyen said that the EU should act very swiftly, decisively, and as one. She added that all air travel to South African countries should be stopped to limit the movement of the new variant.

Difficult words: mutation (a change in the structure of the genes of an organism), spike protein (a member of the coronavirus family that has sharp bumps known as spikes), hasty (done in a hurry, sometimes without the necessary care or thought).