Danish authorities said Friday they were investigating several cases of people found to have been infected with a mutated coronavirus transmitted from minks.
The announcement comes a day after Prime Minister Mette Frederiksen introduced a shutdown in a northwestern region of the country where the strain was identified.
Denmark has since ordered the culling of all 15 million mink bred in the country's 1,139 mink farms.
The coronavirus evolves constantly and scientists and experts at the World Health Organization (WHO) said that to date, there is no evidence that any of the mutations pose an increased threat to humans.
The Danish government, however, defended its new measures and reiterated that the strain was found to weaken the ability to form antibodies and could make future vaccines ineffective. Authorities said they would not take any chances and planned to continue the culling process.
"These are timely and necessary measures" amid a "worrying" development, said Foreign Minister Jeppe Kofod.
Five new variants
Denmark has identified five variants of the virus stemming from mink, but only one, known as cluster 5, showed "reduced sensitivity" towards antibodies, according to Denmark's State Serum Institute (SSI) for infectious diseases.
At least 214 people have been infected with a variant of the coronavirus that appeared in minks in June, said SSI.
The tally included 200 people in the region of North Jutland, which is home to most of the country's mink farms.
So far 12 people have been diagnosed with the strain from cluster 5, though they have not shown more severe symptoms than others.
Viruses from cluster 1 have not shown reduced susceptibility to antibodies, while results were pending for the other variants from clusters 2-4, according to SSI.
WHO looks to step up biosecurity
The WHO said it wants to strengthen biosecurity efforts around mink farms across the world.
"We are working with regional offices ... where there are mink farms, and looking at biosecurity and to prevent spillover events," Maria van Kerkhove, WHO's COVID-19 technical lead, said at a briefing in Geneva.
Kerkhove said Denmark's decision to cull its mink was aimed at preventing the establishment of "a new animal reservoir for this virus."
WHO pandemic response chief Mike Ryan emphasized the need to prevent virus transmission between minks and humans, given that the virus can evolve within these animals, especially if they are closely packed together in farms.
He noted that other farm animals, such as pigs and poultry, had "very strict" biosecurity measures in place to prevent viruses jumping between species.
The WHO's chief scientist, Soumya Swaminathan, however, said it was too early to jump to conclusions.
"We need to wait and see what the implications are but I don't think we should come to any conclusions about whether this particular mutation is going to impact vaccine efficacy," she said. "We don't have any evidence at the moment that it would."
Cluster 5 has not appeared outside the country and it was not immediately clear why it emerged in Denmark.