Why are Mink a threat to Covid-19 vaccines?

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   In the past month, the possible culling of up to 17 million Mink has been ordered in Denmark due to genetically mutated strains of SARS-CoV-2 having spread through the population. Through samples representing approximately 20% of the country’s confirmed Covid-19 cases, it can be seen that about 300 variants of the virus trace back to Minks with almost 170 variants identified through sequenced viral samples from 40 Mink farms. However, it must be noted that no evidence has been found that these mutations pose an increased danger to people in comparison with the standard strain. [1][2]

   This spread is currently assumed to be due to Minks catching the virus from infected workers as a result of their susceptibility to respiratory viruses, and then returning the slightly genetically altered versions back to humans with the transfer being the result of infectious droplets, bedding and excretion containing dust. With 2.85 million Mink already having been put down, the particular strain concerning scientists most – cluster-5 – has only affected 12 people and has not been detected since September.[3]

   Cluster-5 is of particular worry for scientists due to its mutations to the spike protein of the virus. The concern is due to the role of spike proteins in allowing the infectious virus to enter the host cell’s bodies. The head of the spike protein recognises receptors on the host cell and binds to them, leading the proteins stalk to fuse the virus envelope with the host cell membrane. The cluster-5 variant causes two deletions and three amino-acid changes to the virus’ spike protein – major changes.[4]

   This change in spike protein composition poses a challenge for vaccine development due to the significance of the protein in the spread of the virus. Targeting the spike protein would prevent the virus from interacting with the host cells. However, vaccines would only be made to target a specifically shaped spike protein to be effective. Subsequently, the alteration caused by the cluster-5 variations would be resistant to the new vaccine if it targeted only the protein. Additionally, preliminary cell experiments that have been carried out suggest that antibodies find it more difficult to fight the cluster-5 variation due to hindered recognition of the virus itself.

   However, despite the affected spike protein, researchers still maintain the opinion that the mutations themselves are not particularly concerning as there is little evidence to show the virus spreads easily among people; the workers picking up the virus as a result of being exposed to high viral doses. Therefore, the risk of it becoming more deadly due to inhibition of vaccines is unlikely. Nevertheless, the culling is still deemed necessary because of the rapid and uncontrolled spread in the Mink themselves; more than 200 farms affected since only June.      

The fears of mutated spike proteins causing difficulties in vaccine production can be foreseen with the current developments in the Moderna and Pfizer vaccines. Both vaccines contain mRNA sequences that code for the coronavirus’ spike protein, that when injected into the body, causes the host cells to produce many copies of the spike protein. Subsequently, the immune system can be triggered to create antibodies specific to the spike protein that would then be available as a secondary response if the person were to come into contact with the live virus at a later stage. Therefore, the culling of an entire population of Mink could be deemed justifiable as to prevent the much-needed vaccines becoming redundant. This despite making Danish Mink almost completely extinct whilst concurrently having significant negative impacts on Mink farmer’s livelihoods around the country. [5]

   This rapid spread of the virus in Mink has led to the culling in several countries with others such as Ireland also considering it. [6]


References

  1. Adrienne Murray, ‘Coronavirus: Denmark shaken by cull of millions of mink’, BBC, Nov. 11, 2020, https://www.bbc.co.uk/news/world-europe-54890229
  2. Smriti Mallapaty, ‘COVID mink analysis shows mutations are not dangerous — yet’, Nature, Nov. 13, 2020, https://www.nature.com/articles/d41586-020-03218-z#correction-0
  3. Helen Briggs, ‘What’s the science behind mink and coronavirus?’, BBC, Nov. 9, 2020, https://www.bbc.co.uk/news/science-environment-54842643
  4. Benedette Cuffari, M.Sc. ‘What are Spike Proteins?’, News Medical Life Sciences, Jun. 12, 2020, https://www.news-medical.net/health/What-are-Spike-Proteins.aspx
  5. James Paton, ‘The Two Vaccines Have Much in Common’, Bloomberg, Nov. 17, 2020, https://www.bloomberg.com/news/newsletters/2020-11-17/pfizer-pfe-moderna-mrna-covid-19-vaccines-what-we-know-do-they-work
  6. Jane Dalton, ‘Covid: Ireland set to cull all 120,000 mink on its fur farms over fears of virus spreading’, Independent, Nov. 20, 2020, https://www.independent.co.uk/news/world/europe/covid-mink-ireland-cull-fur-farm-b1750865.html

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