The highly infectious variant of coronavirus that has emerged in south-east England is spreading rapidly to the rest of the UK and is already present elsewhere in the world, scientists warned on Sunday. The World Health Organisation said its Evolution Working Group is working closely with the UK medical authorities to understand how the variant, now called B.1.1.7, is likely to affect the course of the pandemic. It has been detected in the Netherlands, Denmark and Australia.

Scientists say two aspects of B.1.1.7 give cause for concern. One is the unprecedented number of mutations it carries. The other is the speed with which it is supplanting other strains of the Sars-Cov-2 virus in south-east England. Jeffrey Barrett, director of the Covid Genomics Initiative at the Wellcome Sanger Institute, said 23 letters in the viral genetic code had changed, of which 17 might affect the behaviour of the virus — in particular helping it to enter and propagate within human cells.

“This new variant is very concerning, and is unlike anything we have seen so far in the pandemic,” he said. There is no evidence so far that the mutations are affecting the course of illness in people who have infected with B.1.1.7 or the effectiveness of Covid-19  vaccines under development. “Hospitalisation rates have gone up recently [in south-east England] but roughly in line with the increase in case numbers, which doesn’t point to the new strain leading to more severe symptoms,” said Francois Balloux, director of the UCL Genetics Institute in London.

“I’d be very surprised if any evidence arose that it creates more serious symptoms,” Prof Balloux added. “It’s also not a strain that should be able to escape protection provided by immunisation caused by the current vaccines or prior infection. ” But Kristian Andersen, director of infectious disease genomics at Scripps Research Institute in California, said: “I have seen many articles stating ‘no effect on immunity or vaccines or clinical features. That is not correct . . . The fact is we don’t know but we will in the coming weeks.”