Maria van Kerkhove, the WHO’s technical lead for COVID-19, told a briefing in Geneva on Friday that transmission of the virus between animals and humans was “a concern”.

But she added: “Mutations (in viruses) are normal. These type of changes in the virus are something we have been tracking since the beginning.”

The risk was much lower in other farm animals than mink, which appear to be much more susceptible to infection, a second WHO expert said.

“We are working with regional offices … where there are mink farms, and looking at biosecurity and to prevent spillover events,” van Kerkhove said.

Denmark said this week it plans to cull its entire mink population and announced strict new lockdown measures in the north of the country to prevent a mutated coronavirus from spreading in the animals and to humans.

It has raised concerns that the mutations could affect the potential efficacy of COVID-19 vaccines in development.

Soumya Swaminathan, the WHO’s chief scientist, said on Friday, however, that it is too early to jump to conclusions about the implications of mutations in the virus found in mink.

“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.”

MUTATED STRAIN

Denmark’s State Serum Institute, which deals with infectious diseases, said a mutated strain of the SARS-CoV-2 coronavirus had been found in 12 people and on 5 mink farms.

Kerkhove said Denmark’s decision to cull its mink was aimed at preventing the establishment of “a new animal reservoir for this virus”.

Mike Ryan, the WHO’s top emergencies expert, said the WHO would complete a risk assessment of the incident and share it with WHO members within hours.

Coronavirus is thought to have first jumped from animals to humans in China, possibly via bats or another animal at a food market in Wuhan, although many outstanding questions remain.

Other mammals have been known to catch it such as cats. Others, such as mice and ferrets, are being intentionally infected with it for medical research.

“There’s always the potential that this can come back to humans,” Ryan said. “That is a concern because mammal species like mink are very good hosts and the virus can evolve within those species especially if they are in large numbers packed closely together.”

But Ryan added that other farm animals, such as pigs and poultry, had “very strict” biosecurity in place to prevent viruses jumping the species barrier. (Additional reporting by Michael Shields in Zurich, editing by Alex Richardson, Louise Heavens and Timothy Heritage)