No evidence to suggest coronavirus cluster 5 variant found in minks increases virus transmissibility, disease severity

So far, six countries — Denmark, the Netherlands, Spain, Sweden, Italy and the U.S. — have reported SARS-CoV-2 in farmed minks, says WHO

Updated - November 08, 2020 12:15 am IST

Published - November 07, 2020 05:48 pm IST - CHENNAI

Denmark had on November 6 ordered culling of the entire farmed mink population of 17 million to prevent further changes to the virus emerging among minks.

Denmark had on November 6 ordered culling of the entire farmed mink population of 17 million to prevent further changes to the virus emerging among minks.

Since June, 214 people in Denmark have been reported to have been infected with a variant of the novel coronavirus associated with farmed minks . This includes 12 cases reported on November 5 in people aged 7-79 years who had a link with mink farming; four cases were through human-to-human transmission of the variant. So far, six countries — Denmark, the Netherlands, Spain, Sweden, Italy and the U.S. — have reported SARS-CoV-2 in farmed minks, the World Health Organization (WHO) says.

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The variant called “cluster 5” has a combination of mutations not seen previously. Cluster 5 makes up around 5% of the strains found in northern Denmark. So far, this variant has not been reported from other countries, suggesting that the variant has not spread beyond Denmark.

Denmark had on November 6 ordered culling of the entire farmed mink population of 17 million to prevent further changes to the virus emerging among minks, and the spread of mink-related viruses any more from minks to humans.

Significance of the variant

According to the WHO, initial observations suggest that the “clinical presentation, severity and transmission among those infected are similar to that of other circulating SARS-CoV-2 viruses”. It further added: “The implications of the identified changes in this variant are not yet well understood. Preliminary findings indicate that this particular mink-associated variant identified in both minks and the 12 human cases has moderately decreased sensitivity to neutralizing antibodies.”

Denmark epidemiologist Kare Molbak said cluster 5 was not more dangerous than other strains or more infectious, according to Reuters .

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“Scientists have not yet noted changes to the mink-related strain of the virus identified in Denmark that affect transmissibility, disease severity or reinfection in people. But further evidence is needed,” WHO tweeted. Further studies are needed to understand the significance of the variant in terms of diagnostics, therapeutics and vaccines in development.

Prof. Francois Balloux, Director of UCL Genetics Institute, U.K. said in a tweet that his colleagues had previously identified mutations in the virus, including one in the Spike protein, occurred repeatedly in minks, which may be involved in increased transmission in carnivore hosts.

Prof. Balloux further said: “SARS-CoV-2 mutations acquired in minks are not concerning. We already knew that SARS-CoV-2 can transmit from minks to humans. Though, this should be of no concern in terms of the evolution of the transmissibility of the virus.”

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In a tweet thread, Prof. Balloux explained that the variant seen in mink, which has also spread to humans, may not increase the ability of the virus to spread. “The population of SARS-CoV-2 is so large that any mutation viable to the virus has arisen many times by now. There is no evidence that any such mutation affects transmissibility in humans (with the possible, questionable exception of D614G),” he noted. “There are thousands of mutations in SARS-CoV-2 arising constantly. The fact that a few have been observed in minks will not change the strains in circulation in humans. If they were beneficial for the virus to infect its human host, they would be at high frequency already.”

Impact on vaccine efficacy

“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,” says WHO’s Chief Scientist Dr. Soumya Swaminathan. “We don’t have any evidence at the moment that it would.”

Prof. Balloux has been more critical of news reports suggesting that the variant might impact vaccine efficacy. “The ‘vaccine escape’ scare story is just idiotic. Vaccine-escape mutations may (or not) arise in humans in the future, if they are advantageous to the virus for (once vaccines will be deployed). They definitely won’t be fuelled by mutations having emerged in minks,” he tweeted.

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Jumping across species

The virus had jumped to minks from humans infected with SARS-CoV-2. Mink and humans have a similar biological trait regarding a so-called ACE2-enzyme expressed by cells of the respiratory tract, which makes it easier for mink to be infected with a virus that has adapted to humans, Allan Randrup Thomsen, a virologist at Copenhagen University, told Reuters.

“Minks can act as a reservoir of SARS-CoV-2, passing the virus between them, and pose a risk for virus spill-over from mink to humans. People can then transmit this virus within the human population. Additionally, spill-back (human to mink transmission) can occur,” the WHO says.

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“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,” Mike Ryan of WHO says.

“It is normal for viruses to mutate or change over time. But each time a virus goes from humans to animals and back to humans, it can change more. That’s why these reports are concerning,” WHO tweeted.

Four of the latest 12 people who were from the local community already indicates the ability of the variant to spread from one person to another.

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Animals getting infected with SARS-CoV-2 remain a concern as the infected animals could contribute to amplifying and spreading the virus. While mutations arise even when the virus spreads amongst humans, genetic modifications in the virus not seen so far can occur when the virus jumps from humans to animals and back to humans, as seen now.

The spread of the variant from mink to humans “highlights the important role that farmed mink populations can play in the ongoing transmission of SARS-CoV-2 and the critical role of strong surveillance, sampling and sequencing SARS-CoV-2, especially around areas where such animal reservoirs are identified,” the WHO noted.

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