The U.K. variant of the coronavirus has developed a new, concerning mutation in a small number of cases, which scientists said makes it similar to the South African and Brazilian variants and could reduce the efficacy of vaccines.
The emergence of the mutation to the variant first discovered in Britain highlights how complicated exiting COVID-19 lockdown will be even once vaccines are rolled out.
Public Health England said there had been 11 reports of the UK variant which feature the E484K mutation, mostly in south-west England.
The E484K mutation, which occurs on the spike protein of the virus, is the same change as has been seen in the South African and Brazilian variants that have caused international concern.
"PHE is monitoring the situation closely and all necessary public health interventions are being undertaken, including enhanced contact tracing and control measures," a PHE spokesman said.
Several laboratory studies have found that vaccines and antibody therapy are less effective against the South African variant.
By contrast, early evidence showed that vaccines worked just as well against the UK variant, which originally did not have the E484K mutation.
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Health minister Matt Hancock said it was too early to tell the impact of variants on vaccines, but mutations of concern had been reported in Bristol and Liverpool.
"We must continue to act with caution, not least because of the renewed challenges posed by new variants of the coronavirus," he told lawmakers.
Calum Semple, who is part of a panel that advises the British government, told BBC radio that E484K was the "mutation of most concern", and had "occurred spontaneously" in the UK variant.
The name E484K, in layman's terms, is like map coordinates. The number 484 is the exact location of the mutation, the letter E is the amino acid that it was originally and the letter K is the amino acid that it has mutated to.
Concern over the South African variant, with its E484K mutation, has already prompted authorities in England to begin a door-to-door mass testing drive in areas where cases of the variant have been found in people with no link to South Africa, while mandatory quarantine in hotels for arrivals from South Africa is yet to come into force.
Though the number of reported cases of the UK variant with the concerning mutation are small, scientists said that it demonstrated how Britain's high prevalence of cases meant that it was not enough simply to prevent new variants being imported.
"This report would seem to suggest that under conditions of very high levels of virus replication even the most stringent of border controls, although they may delay spread, are unlikely to prevent the appearance of new variants," said Jonathan Stoye, virologist at The Francis Crick Institute.
The initial British variant, known as B.1.1.7, has been found in 467 people in 32 U.S. states. Florida leads in cases, with at least 147, followed by California, with 113 known cases.
L.A. County officials announced the second confirmed case Saturday and said it is "spreading in the county," while officials in San Diego and San Bernadino have also identified cases.
Sweden also has seen an increased spread of the British COVID variant, with 11% of screened positive tests showing the mutation, thought to be a more contagious form of the virus, the Public Health Agency said on Tuesday.
Out of a total of 2,220 positive samples that were screened for the British variant, about 250 were found to be of that strain.
The Health Agency also said it would not use Astra Zeneca's COVID vaccine for people over 65, citing lack of evidence it was effective for that group.
Sweden, which has shunned lockdowns throughout the pandemic, registered 9,649 new coronavirus cases since Friday, Health Agency statistics showed on Tuesday.
The figure compares to 9,123 cases the corresponding period last week.
The country of 10 million inhabitants registered 224 new deaths, taking the total to 11,815. The deaths registered have occurred over several days and sometimes weeks.
Sweden's death rate per capita is several times higher than that of its Nordic neighbours, but lower than in several European countries that opted for lockdowns.