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The government has said it is urgently investigating the new coronavirus variant amid warnings it "could defeat the vaccine".
The UK is one of a number of countries to respond to the emergence of the new strain that experts have warned could be the "worst we've seen so far".
On Friday, transport secretary Grant Shapps said the UK was taking a "safety-first approach" by suspending flights from six southern African countries.
He said ministers acted “extremely fast”, warning: "We can’t take risks when we see a variant which could well defeat the vaccine, or at least that’s the concern and we need just a bit of time to check that out.”
Health Secretary Sajid Javid said in a statement on Friday that the variant was “of huge international concern”.
He added it “is highly likely that it has now spread to other countries”, adding: “We are concerned that this new variant may pose substantial risk to public health.".
He confirmed early indications show the current vaccines “may be less effective against it”.
'Most worrying we've seen'
UK scientists first became aware of the new strain - called B.1.1.529 - on November 23 after samples were uploaded to a coronavirus variant tracking website from South Africa, Hong Kong and then Botswana. A total of 59 samples have been uploaded on to the website so far, but there are around 100 confirmed cases in South Africa.
There are no cases in the UK, and it has not yet been classed as a “variant of concern” because scientists do not have enough evidence on its levels of transmissibility.
However, senior officials have said they are concerned.
Dr Susan Hopkins, the chief medical adviser at the UK Health Security Agency, said the new variant is the most “complex” and “worrying” seen so far.
Watch: What we know about the variant
“The first look at it shows it has a variety of different mutations, it’s got 30 different mutations that seem relevant, that’s double what we had in Delta," she said.
"And if you look at those mutations as mutations that increase infectivity, mutations that evade the immune response, both from vaccines and natural immunity, mutations that cause increased transmissibility, it’s a highly complex mutation, there’s new ones we haven’t seen before, so we don’t know how they’re going to interact in common.
“So all of this makes it a pretty complex, challenging variant and I think we will need to learn a lot more about it before we can say for definite its definitely the most complex variant before.”
She added: “It is the most worrying we’ve seen.
Professor James Naismith, director of the Rosalind Franklin Institute, said the new variant will “almost certainly” make the vaccines less effective.
Asked if it is highly transmissible, he added: “We don’t really know that’s for sure yet.
“It has mutations consistent with the Delta variant, which does spread more quickly, but transmissibility and spread is not just as simple as this amino acid does this or this does that, it’s more like a team on things.
Dr Mike Tildesley, a member of the Scientific Pandemic Influenza Modelling group (Spi-M), which advises Government, said it was “very, very early days” in understanding the new variant and whether it may affect vaccines, whether it spreads more rapidly or is more deadly.
Prof Lawrence Young, Virologist and Professor of Molecular Oncology, University of Warwick, said: “This new variant of the COVID-19 virus is very worrying. It is the most heavily mutated version of the virus we have seen to date. This variant carries some changes we’ve seen previously in other variants but never all together in one virus."
How is it different from the other variants?
Despite only being tracked for the past three days, the virus has been identified as having 30 different mutations already. By comparison, that is twice as many as the Delta variant, which has been the most prominent variant in the UK over the past few months.
The mutations contain features seen in all of the other variants but also traits that have not been seen before.
It’s too early to say if it will defeat the vaccine. The mutations could potentially make the variant more transmissible and evade the protection given by prior infection or vaccination.
Professor Neil Ferguson, a member of the Scientific Advisory Group for Emergencies (Sage), said: “The B.1.1.529 variant has an unprecedented number of mutations in the spike protein gene, the protein which is the target of most vaccines.
“There is therefore a concern that this variant may have a greater potential to escape prior immunity than previous variants.
“However, we do not yet have reliable estimates of the extent to which B.1.1.529 might be either more transmissible or more resistant to vaccines, so it is too early to be able to provide an evidence-based assessment of the risk it poses.”
The World Health Organization is monitoring the development of the variant.
The WHO said they would convening a meeting on Friday "to better understand the timeline for studies that are underway and to determine if this variant should be designated as a variant of interest or variant of concern."