A scientist has warned of a new mutant hybrid of British and US variants of Covid.
Dr Bette Korber says the 'recombination' strain could allow the virus to be more infectious while also being more resistant.
The new strain is made up partly of the highly-transmissible variant that originated in Kent.
It raises worries that the world could be on the brink of a new phase of the Coronavirus pandemic.
The B117 strain was first discovered in England before the third national lockdown, The Mirror reports.
It's believed that it has mutated with another that has been spreading across Los Angeles, a variant that is resistant to antibodies.
A report by New Scientist states that unlike previous mutations, a recombination could bring multiple mutations together in one go.
It would still only occasionally confer more advantage of the original strains, the report continues.
Dr Bette Korber discovered the mutant strain at Los Alamos National Laboratory in New Mexico, sharing it with other experts at a New York Academy of Sciences meeting on February 2.
She said she had "pretty clear" evidence of the strain, though it has not yet been confirmed.
Dr Korber, a computational biologist, said: "This kind of event could allow the virus to have coupled a more infectious virus with a more resistant virus."
Two research groups said they hadn't seen any evidence of recombinations in their studies performed in December and January.
As the strain has not been confirmed, it's unclear whether a hybrid would be more dangerous, or what impact the new discovery would have on society.
It's likely that SARS-Cov-2 - which started the pandemic - is a recombination itself.
Sergei Pond, of Temple University in Pennsylvania, said: "We may be getting to the point when this is happening at appreciable rates."
The professor is unconvinced of widespread hybrids at present, adding: ""coronaviruses all recombine, so it’s a question of when, not if".
