Analysis: Does the coronavirus mink mutation pose a genuine risk in the fight against Covid-19?

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Denmark has taken the drastic step of culling millions of minks following the emergence of a new coronavirus strain which has passed from the weasel-like animal to humans.

Numerous mutations have been detected in Sars-CoV-2 throughout the pandemic – yet scientists have warned that this particular variant could impact the effectiveness of future vaccines.

A total of 12 people have been infected with this “cluster 5” strain so far, with all of the cases detected in Denmark’s North Jutland region.

The World Health Organisation (WHO) said this variant featured a combination of mutations that have not been previously observed, and warned that it appeared to show “moderately decreased sensitivity” to the body’s neutralising antibodies.

Here, we take a closer look at this new development.

How did this new mutation arise?

The WHO said the animals will have contracted Sars-CoV-2 “following exposure from infected humans” before it spread through Denmark’s vast mink farming industry. As the virus was passed from one mink to another, it will have undergone genetic mutations that enabled it to adapt to its new host.

Strains of coronavirus have been previously detected in mink farms in the Netherlands, Sweden and Spain, yet the cluster 5 variant appears to have been successful in making the jump back into humans – a process that is believed to drive further genetic mutation.

Professor Francois Balloux, director of the Genetics Institute at University College London, said that minks are “very susceptible” to infection.

“There is good evidence when the virus jumps into minks and circulates – as they are caged, it spreads like wildfire – it seems to adapt,” he told The Independent. “It acquires some mutations that we only very exceptionally see in humans.”

Jeffrey Barrett, a professor of respiratory medicine at the Liverpool School of Tropical Medicine, said this “this kind of development is to be expected” and that the “virus is mutating all the time, in both humans and any animals it infects”.

How widespread is the outbreak?

Since June 2020, 214 human cases of Covid-19 in Denmark have been linked to mink variants of Sars-CoV-2, the WHO said last week. This includes 12 cases of the cluster 5 strain, all of which have been identified in the northern tip of Denmark.

Those who were infected ranged in age from seven to 79 years, and eight had a link to the mink farming industry while four cases derived from the local community.

Hans Kolmos, a professor of clinical microbiology at the University of Southern Denmark, said: “We cannot be sure that we have seen all of the cases. And we cannot be sure that something even more dramatic won’t appear in the future from future mutations.”

What does this new mutation look like?

Details of the genetic sequencing for this strain have yet to be fully reviewed by scientists, though it appears the mutation has been located within the so-called “spike” protein that allows Sars-CoV-2 to attach to human cell receptors.

Ian Jones, a professor of virology at the University of Reading, said: “The idea that the virus mutates in a new species is not surprising as it must adapt to be able to use mink receptors to enter cells and so will modify the spike protein to enable this to happen efficiently.”

This variation does not seem to have made the virus more contagious or potent, though concern has been raised how over it interacts with the body’s neutralising antibodies.

So does this mean it could impact the effectiveness of a vaccine?

The Danish Statens Serum Institute has reported that this variation of the virus is not as easy to inactivate with antibodies from recovered patients. “This could potentially be worrisome in terms of vaccines, if the antibodies raised by vaccination are less effective against the virus with this mutation,” Prof Barrett told The Independent.

Prof Balloux said it was possible that this genetic variation to Sars-CoV-2 could reduce the effectiveness of future vaccines “a little bit” but insisted it wouldn’t derail efforts to develop an efficacious jab. “This mutation that has been acquired in minks is not more or less concerning than other variations,” he said.

Robin Shattock, who is leading the development of the Imperial College London vaccine, said that it wouldn’t be difficult for scientists to adapt those Covid-19 jabs that use RNA technology, such as the Pfizer/BioNTech and Moderna candidates, to future strains.

The Pfizer vaccine candidate has 90 per cent efficacy, early data has shown, in news celebrated as a “great day for science and humanity.”

“It’s all based on sequence, you just change the sequence or include an additional sequence to accommodate any changes needed,” Prof Shattock told The Independent. “It's something we have to monitor very carefully so that if there are changes that get around the activity of any of the vaccines, we can spot that really early and be ahead of it.”

There is a possibility that future strains of Sars-CoV-2 could enable it to get around certain vaccines, but with so many technologically diverse candidates in development at the moment, it’s likely these should “help counteract any escape mutations”, says Prof Barrett.

What action have the authorities taken?

Danish officials are culling all farmed mink, which amounts to roughly 17 million animals, at an estimated financial loss of 5 billion kroner (£600m). The prime minister apologised on Tuesday for ordering the cull without the necessary legislation in place. 

“The government has decided from a precautionary principle to take out all mink herds and simply kill the animals because we cannot control the transmission and we cannot be sure that this will not occur in the future too,” said Prof Kolmos.

Testing has been ramped up in north Jutland, while restrictions between the region and other parts of Denmark have been enforced to prevent further community transmission of the new strain.

The genome sequence of the cluster five variant has also today been released, allowing scientists across the world to take a closer at the new strain and acquire a greater understanding of its potential threat.

In the UK, all international travel to and from Denmark has been banned. British nationals or residents who are returning from the country, whether directly or indirectly, can still travel to the UK but must fully self-isolate along with all other members of their household.

Additionally, freight drivers who are not UK citizens and have been through Denmark in the last fortnight are warned they will be turned away from the British border.

Downing Street has meanwhile said there is no evidence to suggest that the mink strain has begun circulating in the UK population.

The prime minister’s official spokesperson said: “There are no fur farms in the UK so we’re not at risk in that regard. There's no evidence to suggest that this new strain is currently in the UK.”

Is there a genuine cause for concern?

At this stage, the picture is mixed. Virologists have said that mutations in the virus are to be expected, and that any jump into animals – as we’ve seen here – will accelerate these genetic changes.

Currently, it’s unclear what this new strain is really capable of. As well as the potential risk it poses to our vaccines, there is also the danger it could spill over into other animal populations, where it would likely undergo further mutation. However, the reality is that further evaluation of the data is needed before any firm conclusions can be drawn.

Authorities in Denmark have acted quickly in bid to halt any further spread of the virus from minks to humans, though at this stage the main source of transmission will be between people. Culling minks is therefore unlikely to make this variant disappear.

But while this development has sparked justifiable concern, there is confidence that this latest development won’t bring us back to square one in the fight against Covid-19. “It’s important not to panic,” says Prof Barrett. “The world has sequenced well over a 100,000 viral genomes, and the mink mutations so far are extremely rare in people.”