COPENHAGEN (AFP, REUTERS) - Denmark announced special restrictions for more than 280,000 people in the north-west of the country on Thursday (Nov 5) after a mutated version of the new coronavirus linked to mink farms was found in humans.

Copenhagen warned that the mutation could threaten the effectiveness of any future vaccine.

"From tonight, citizens in seven areas of north Jutland are strongly encouraged to stay in their area to prevent the spread of infection," Prime Minister Mette Frederiksen told a news conference.

She said people were being ordered not to travel there, while bars and restaurants would also shut.

"We are asking you in north Jutland to do something completely extraordinary," Frederiksen said, talking of a "real closure" of the region. "The eyes of the world are on us," she added.

Public transport in the region will be shut down with buses and trains stopped from entering or leaving. Some schoolchildren will have to follow their classes online in restrictions that are due to last a month.

Denmark, the world's largest exporter of mink fur, raised concerns on Wednesday by announcing the slaughter of all mink in the country - numbering 15 to 17 million spread over 1,080 farms - following the discovery of the mutation which can be passed to humans.

The mutation has already been detected in 12 people - 11 cases in the region being closed down, and one in another.

Scientists say virus mutations are common and often harmless. Some experts have nevertheless called on Denmark to release more scientific data to better evaluate this one.

A World Health Organization official said on Thursday that mink appear to be susceptible to the new SARS-CoV-2 virus and "good reservoirs" for the disease.

"So there is a risk of course that this mink population could contribute in some way to the transmission of the virus from minks into humans, and then onwards from humans to humans," Catherine Smallwood, a senior emergency officer at WHO's European office in Copenhagen, said in a social media event.

While the research into this specific variant of the virus is significant, she said it's "totally normal" for the virus to change genetically over time.

"We are tracking these (changes) very very carefully and that's why we are so interested in this particular information,"she said, adding that it should not alter how governments and authorities around the world are trying to control the pandemic.

Hans Kluge, WHO European regional director said Denmark showed "determination and courage" in the face of a decision to cull its mink population of 17 million animals, which has a "huge economic impact".

According to Danish authorities, this virus mutation doesn't cause a more severe illness in humans. But it is not inhibited by antibodies to the same degree as the normal virus, which they fear could threaten the efficacy of coronavirus vaccines that are being developed around the world.

In north Jutland, health authorities believe around five per cent of coronavirus patients could be carrying this mutated strain, but no recent case has been reported. As such, Viggo Andreasen, epidemiology professor at Roskilde University, said the mutation had "quite a good chance" of disappearing, as long as it is effectively contained.

Denmark, a 5.8-million-strong country, has been relatively spared from the ravages of Covid-19 with 733 deaths reported. But it imposed new national restrictions in October to curb a rapid spike in cases.

In a report published on Wednesday, the State Serum Institute (SSI), the authority dealing with infectious diseases, said laboratory tests showed the new strain had mutations on its so-called spike protein, a part of the virus that invades and infects healthy cells.

That poses a risk to future Covid-19 vaccines, which are based on disabling the spike protein, SSI said.

Ian Jones, a virology professor at Britain's University of Reading, said the virus would be expected to mutate in a new species. "It must adapt to be able to use mink receptors to enter cells and so will modify the spike protein to enable this to happen efficiently," he explained.

"The danger is that the mutated virus could then spread back into man and evade any vaccine response which would have been designed to the original, non-mutated version of the spike protein, and not the mink-adapted version."

James Wood, a professor of veterinary medicine at Cambridge University, cautioned that the true implication of the changes in the spike protein had not yet been fully assessed by scientists. "It is too early to say that the change will cause either vaccines or immunity to fail," he said.