The study, published last week in the scientific journal Frontiers in Microbiology, goes some way towards excusing the mink cull, which has been seen as the Danish government’s biggest misstep during the pandemic.
“Blood samples have been taken from people who have recovered from covid-19 infection with cluster 5 and we looked at how well their antibodies could neutralize this virus,” Tyra Grove Krause from the SSI, told the Ritzau newswire.
“You can see that cluster 5 is more resistant to these antibodies than the other virus variants that were in circulation at the time. So on that basis, one can say that this raises concerns about whether the same could apply to vaccine antibodies.”
In an independent study, the SSI researchers also found that the Cluster 5 spike changes were associated with a more than threefold decrease in “neutralization titres” in people immunized with the Pfizer vaccine, indicating a lower antibody response.
“Ultimately, the combination of spike changes in the Cluster 5 variant conferred a degree of resistance to neutralizing antibodies in a proportion of convalescent COVID-19 people,” the article concluded.
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In a press release issued on Monday, the SSI said that the virus had continued to evolve rapidly in the mink population, an observation also made in the article.
“Following the Cluster 5 discovery, a mink-associated SARS-CoV-2 variant with six spike protein changes appeared (L5F, ΔH69/V70, Y453F, D614G, N751Y, and C1250F),” the authors wrote. “Thus, the virus continued to acquire spike protein changes through its passage in mink.”
Krause said that it had been this continuing evolution which had made the development in mink so worrying.
The SSI does not, however, recommend a total cull, if coronavirus is identified among herds of farm animals, advising that the infection instead be closely monitored, controlled and limited.
Almost all Denmark’s mink were killed during the last months of 2020. In February this year, the Danish Veterinary and Food Administration confirmed that all the country’s mink had been slaughtered.
The parliament has since made it illegal to keep mink in Denmark until 2022.