The UK ordered patients suspected of contracting a virus from mink in Denmark into isolation as fears that the mutated coronavirus strain could undermine vaccine efforts increased.
Hospitals were told to quarantine and gene test coronavirus patients who recently travelled from Denmark.
Doctors were told the strain showed "less sensitivity for neutralising antibodies", The Telegraph said.
Patients who recently travelled to Denmark must not be offered routine outpatient, ambulatory or primary care, an alert to British doctors said.
If patients tested positive for coronavirus they must be treated in specialist centres, it said.
Known as cluster five, the variant has four mutations in the spike protein, the part of the virus scientists put into vaccines to help drive antibodies.
The mutated strain is believed to have jumped from farmed mink to humans in northern Denmark in June.
There are now more than 200 patients with coronavirus infections linked to mink farms.
At the weekend, the UK banned entry to all non-residents coming from Denmark, while UK citizens must isolate for two weeks.
The travel ban came as vets began the grim task of gassing and burning 17 million mink to help stop the spread of the strain.
Scientists said virus mutations are common and often harmless, and this one does not cause a more severe illness in humans.
But Prof Wendy Barclay, a biologist at Imperial College London, said the mink strain was unusual and should be taken seriously because of the risk to the vaccine.
Speaking on BBC Radio 4's Today programme, she said: "If the spike protein of the virus is now different to it was when we first started developing the vaccine, there would be a mismatch.
“The protection we get might not be as good as we want it to be.”
Prof Barclay said that it was still unclear how damaging the new strain could prove, but authorities should monitor it.
“It’s so important we group together and work with the Danish,” she said.
The new health measures to quarantine Britons arriving from Denmark mirrored those imposed on returning travellers from Wuhan, central China, at the start of the pandemic.
Foreign Secretary Dominic Raab said on Sunday the ban was the “right decision”.
He told Sky News: “The concern is that you see a mutated version of the coronavirus and that if it spread, it would undermine our ability to make an effective vaccine.
“We need to look very carefully at the science.”
The World Health Organisation (WHO) said Italy, the Netherlands, Spain and Sweden also reported the disease in mink.
It said the implications of the mutated strain were not yet well understood but the variation appeared to be less inhibited by antibodies.