Mink slaughter seeks to save Denmark from being a new Wuhan

The writer is a science commentator

Denmark is desperate not to become the next Wuhan. The country is destroying its entire mink population after a mutated form of coronavirus was found in both animals and mink farm workers. The drastic step, which includes locking down the north-west of the country until December 3, is intended to stop the rise of a virus potentially capable of evading Covid-19 vaccines. The decision is especially significant given Monday’s welcome news that Pfizer and BioNTech’s vaccine appears to be highly effective.

The World Health Organization has hesitated so far to confirm that the cull of 17m animals is necessary. But the country’s foreign minister, Jeppe Kofod, nevertheless defended the decision on Friday: “We would rather go a step too far than take a step too little to combat Covid-19.” By normalising the principle of overreacting, the command from Copenhagen signals an important new precedent in global public health. 

The alarm was raised by the country’s State Serum Institute, which noted that various mutated forms of Sars-Cov-2, the virus that causes Covid-19, were spreading among fur farm animals, and these had passed back again from animals to workers. Five different clusters of mutations have been detected in 214 people in total. Worries have focused on ‘cluster 5’, a unique variant found in a dozen people in North Jutland. 

This form of the virus contains four mutations in the spike protein, which is the portion of the virus recognised by the immune system. Most vaccines are designed to mimic this spike protein in order to generate antibodies. Researchers at the SSI found that coronavirus antibodies taken from recovered patients showed a decreased sensitivity to the cluster 5 virus, suggesting — though not proving — that this particular mutant might be harder for the immune system to recognise and fight off. Of the four other clusters, one did not raise concerns and three are under investigation.

Emma Hodcroft, a Bern University researcher who has gathered public information on the mink variants, has cautioned against panic while also applauding the Danish decision. In a long Twitter thread, she highlighted that “mutations in [the spike protein] are not uncommon”.

Ultan Power, professor of molecular virology at Queen’s University Belfast, has been involved in developing vaccines for respiratory diseases. Virologists, he says, are “perpetually concerned about mutations”, especially those that increase transmission or severity of disease. He adds: “Mutations in proteins like the Sars-Cov-2 spike protein may result in a protein that is no longer recognised efficiently by antibodies to an original infection or a vaccine. Such mutations would have considerable consequences for a vaccine, as the vaccine may not induce protective immunity.” Seasonal flu vaccines are updated every year for this reason. 

Coronavirus is constantly mutating, though relatively slowly. Still, mink farms have become an active reservoir for new variants, with cases also found in the Netherlands, Spain, Sweden, Italy and the US, according to the World Organisation for Animal Health. The Dutch and Spanish culled infected animals. China, the biggest producer, has not reported any cases.

There is both spillover, when the virus goes from animals to people, and “spill back”, when the virus shuttles back from people to animals. Each breaching of the species barrier offers a unique opportunity for multiple genetic changes with unpredictable effects.

That is how the coronavirus pandemic is thought to have started in Wuhan, with the virus probably passed from bats to humans via an intermediate species such as pangolins, a scaly anteater. Earlier intervention might have stopped Covid-19 spreading from China, though we can never predict with certainty any alternative future that might have unfolded.

But we do know, from bitter recent experience, that it is impossible to turn the clock back on a contagious virus left uncontained — and that success may look like overreacting because the threat then fails to materialise. No country wants to be responsible for uncorking a vaccine-resistant strain just as scientists are making headway. It is an unenviable call but, by euthanising an unsustainable industry already on its way out, Denmark deserves praise for learning the lessons of this pandemic.

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