"All remaining mink will now be culled including non-infected and otherwise healthy mink," Denmark's Foreign Minister Jeppe Kofod said in a press conference.
"We would rather go a step too far than take a step too little to combat Covid-19," he said, adding that the Scandinavian country had not overreacted nor taken the decision lightly.
As of Thursday, 216 mink farms in the country were infected with coronavirus and all remaining minks would be culled in line with animal welfare guidelines in the coming weeks, Danish health officials said. Denmark has a total of around 300 mink farms, according to officials.
Earlier, the WHO said it was monitoring the mutation, which was a "concern," but that it was too early to tell if it posed any risk to humans or would undo the impact of a potential vaccine.
"This is a global pandemic and many millions of people have been infected, many millions of animals have been exposed," Dr. Mike Ryan, executive director of the WHO Health Emergencies Program, said during a virtual press conference from Geneva.
"Right now, the evidence that we have doesn't suggest that this variant is in any way different in the way it behaves ... it is still the same virus."
On Thursday, Denmark announced strict new lockdown measures in its northern counties, home to most mink farms, after authorities discovered the mutated strain in the region.
Tyra Krause, a senior public health specialist at Denmark's State Serum Institute, the authority that identified the mutated strain, said although more research was needed, early lab results found "this variant showed less sensitivity" to antibodies, which could make a potential vaccine "less effective."
Krause also predicted "an increase in the coming weeks" in the number of infected patients with the mutated strain, which currently stands at 12 people, she said.
In a report published Wednesday, the institute said tests showed the new strain had mutations on its so-called spike protein, which invades and infects healthy cells. That poses a risk to future Covid-19 vaccines, which are based on disabling the spike protein, it said.
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The WHO's Ryan said although mammal species like mink were "very good hosts," health officials were still a "long, long way away" from any determination on the mutation's impact on a vaccine.
The global public health body would also be looking at biosecurity in other countries that farm mink to "prevent spillover events," Maria van Kerkhove, the WHO's technical lead for Covid-19, said on Friday, adding that the risk from other farm animals and livestock was generally low.
"Mutations are normal," van Kerkhove said. "These types of changes in the virus are something we've been tracking since the beginning."
In the United States, nearly 10,000 minks at nine fur farms in Utah died of Covid-19, state veterinarian Dean Taylor told NBC News last month.
The deaths forced the affected farms to quarantine as the outbreaks were investigated.
The Associated Press and Reuters contributed to this report.