Britain has said it is concerned by a newly identified coronavirus variant spreading in South Africa that might make vaccines less effective and imperil progress made across the world in fighting the pandemic.

The UK Health Security Agency said that the variant — called B.1.1.529 — has a spike protein that was dramatically different from the one in the original coronavirus that Covid-19 vaccines are based on.

Officials characterise the variant, which has double the number of mutations as the currently dominant Delta variant, as the “worst one yet”, according to a Reuters report.

It was only first identified at the start of the week but Britain rushed to introduce travel restrictions on South Africa and five neighbouring countries, acting much more swiftly than with previous variants.