Britain could experience more Covid-19 variants than other countries because a greater proportion of the population has built up immunity, a Sage scientist has suggested.
Prof John Edmunds, a member of the government's Scientific Advisory Group for Emergencies from the London School of Hygiene and Tropical Medicine, said the virus tends to mutate in areas where many people have had it.
The South African and Brazilian variants emerged among populations who had already developed some resistance to the virus, he said, and it may be evolving in order to "evade the immune response".
"In parts of South Africa where the South African variant arose, there was probably quite a high level of immunity in the population at the time," said Prof Edmunds.
"That's also true of the Brazilian variant that we're really concerned about. There's good data to suggest that in Manaus there was high levels of immunity at the time it arose."
The South African variant was first spotted in Britain in December.
There are two Brazilian variants. One – known as P.1 – was detected circulating in Manaus, northern Brazil, by scientists in December. This is the one the government is most concerned about.
A second one - known as P.2. - has been spotted 11 times in Britain and carries a mutation which can bypass antibodies.
Although no cases of the P.1 variant have so far been detected in Britain, Prof Edmunds said he said he would find it "unusual" if it was not already present.
"We're one of the most connected countries in the world, so I would find it unusual if we hadn't imported some of the cases into the UK," he said.
The Government banned flights from South America, Portugal and Cape Verde on Thursday, having previously banned travel from South Africa.
In addition, all quarantine-free travel into the UK will be suspended on Monday in a bid to keep out other variants.
The new policy means arrivals from every destination will need to self-isolate for 10 days, or receive a negative result from a coronavirus test taken at least five days after they enter the UK.
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