A NEW Covid-19 variant found in Brazil could re-infect those who have already fought off coronavirus, experts have confirmed.
The variant led to ministers banning all flights from the country to the UK and other parts of South America - but it has already entered Britain.
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The COG-UK consortium, which has been monitoring new mutations, confirmed the 'P.2 variant' had been detected 11 times in the UK.
It has not yet been classed as "a variant of concern", but it carries a mutation that could make the virus get past immunity developed from previous version of the bug.
A second 'P.1 variant' has also rattled scientists, having caused a huge rise in infections in the city of Manaus, Brazil, and sparking a UK travel ban.
Speaking of the new strains, Professor Wendy Barclay, the head of the G2P-UK National Virology Consortium, said: "There are two different variants that are being talked about in Brazil at the moment, one that was also picked up in Japan and the other which is more prevalent in Brazil at the moment.
"One of them has been detected [in the UK] and one of them has not."
Addressing the P.2 variant specifically, she said it "might impact the way that people's antibodies see the virus".
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Meanwhile Professor John Edmunds, a member of the Government's Scientific Advisory Group for Emergencies (Sage), said he would find it "unusual" if the second of two new variants from Brazil was not already present, despite it not yet being detected.
Prof Edmunds told BBC Radio 4's Today programme: "I don't think there is evidence that we've imported cases of the Manaus strain, as far as I'm aware at least, but it is likely that we probably have quite honestly.
"We are one of the most connected countries in the world so I would find it unusual if we hadn't imported some cases into the UK."
It comes after the Prime Minister last night vowed to tighten Britain's borders over fears of the "vaccine busting" strains.
Boris Johnson announced that all "travel corridors" would be suspended from 4am on Monday.
In a Downing Street press conference last night, he said: "What we don't want to see is all that hard work undone by the arrival of a new variant that is vaccine busting.
Mr Johnson added: "At this crucial stage what we can't have is new variants with unknown qualities coming in from abroad and that's why we've set up the system to stop arrivals from places where there are new variants of concern and set up the extra tough measures that I've outlined."
We are one of the most connected countries in the world so I would find it unusual if we hadn't imported some cases into the UK.
Professor John Edmunds
Meanwhile researchers from the Oswaldo Cruz Foundation, a science institute in Rio de Janeiro, warned that mutations on the new variant could increase the risk of reinfection.
The researchers wrote that "viral evolutions may favour reinfections".
They claimed that recenlty spotted variants "have raised concern on their potential impact in infectivity and immune escape".
In Brazil, an unnamed 45-year-old nurse came down with the new variant in October - five months after she recovered from an older strain of Covid-19.
However, her symptoms were worse the second time she caught the virus.
Earlier this week ministers placed a flight ban on ALL planes coming in from Portugal and all of South America.
It means no-one will be able to fly direct from the dozen nations to the UK - but the USA will be spared.
The strain from Brazil is the third new variant to emerge in the past two months, adding to one identified in the UK, and another in South Africa.
Britain now has three vaccines approved against the coronavirus, from drug giants Pfizer, AstraZeneca (Oxford's) and Moderna.
There are fears the new mutations will be able to dodge the immune system, even after vaccination or previous infection.
Professor Sharon Peacock, who is leading research into new variants in the UK, said some mutations are of "sufficient" concern to need in-depth research in the laboratory.
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And the UK’s Chief Scientific Adviser Sir Patrick Vallance admitted “we don’t know for sure” if the vaccines being rolled out on the NHS will work on the strains from Brazil and South Africa.
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He told ITV's Peston: “There’s a bit more of a risk that this might make a change to the way the immune system recognizes it but we don’t know.
"Those experiments are underway,” Sir Patrick said.