BERLIN — Denmark, one of the largest fur producers in the world, plans to kill every mink in the country to contain a coronavirus mutation that had begun spreading back to humans.

Although the virus mutates constantly, this variation prompted particular concern, according to scientists at Denmark’s Statens Serum Institut, because 12 of the people infected showed less ability to produce antibodies, which could reduce the potential effectiveness of a vaccine.

The Danish government announced it would expand plans for a more limited cull and put down 15 million minks. Prime Minister Mette Frederiksen said Wednesday it was a “heavy decision” but the situation required “resolute action.”

Health Minister Magnus Heunicke said genomic analysis suggested nearly 400 human coronavirus cases in northern Denmark were related to the mink farms, about half of all cases. About 5% of all human infections in the region involve the new mutation, the Serum Institut estimated.

“As a government, we will do everything we can to ensure that the mutated infection is contained and does not spread further,” Frederiksen said. “That’s why — unfortunately — it’s necessary to put down all minks in Denmark.”

In a worst-case scenario, there could be a new pandemic that starts all over again from Denmark, warned Kåre Mølbak, director of the Statens Serum Institut. Independent scientists, however, urged caution, as the institute has not yet publicly released details of the sequencing of the mutation.

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Denmark has more than 1,000 mink farms that produce about 40% of the world’s mink pelts, the majority of which are exported to China and Hong Kong. Minks at 207 farms have tested positive for coronavirus. Denmark plans to compensate mink farmers, but the government said it may be difficult for the industry to survive.

Even though the decision involves killing millions of animals, some welfare groups welcomed it as an opportunity to end to fur farms.

Coronavirus infections have already accelerated plans in the Netherlands to phase out the mink industry, with hundreds of thousands of animals euthanized after outbreaks there.

When the Netherlands began to kill animals in June, it said mink farms risked becoming a “virus reservoir,” presenting a risk to both human and animal health. A September study by Dutch experts found it “very likely” that minks had passed coronavirus back to employees in the first proven case of animal-to-human transmission.

Spain also euthanized nearly 100,000 minks in July, citing concerns that they might be able to spread the virus back to people. There have also been reports of minks contracting the virus at farms in the United States, where thousands of older animals have succumbed to the virus.

But no other country has reported a mink-related mutation that could endanger vaccine efforts.

Concern about animals as vectors has been present since the earliest research into the novel coronavirus. The U.S. Centers for Disease Control does not consider animals to play a significant role in transmission, though minks have been identified as a possible exception.

COVID-19 is considered a “zoonotic” disease, meaning the virus that causes it would have originally come from an animal, possibly a bat. The first reported human cases were linked to a live-animal market in China.