Cluster 5, the coronavirus mutation that spurred the Danish government into culling the country's entire mink stock of over 15 million, has proven resistent to both naturally attained antibodies and those generated by the Pfizer vaccine, a new study by the Danish Serum Institute (SSI) has concluded.
"Blood samples have been taken from people who have recovered from COVID-19 with Cluster 5 and we looked at how well their antibodies could neutralise this virus", Tyra Grove Krause of the SSI said. "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".
The SSI researchers also found that the Cluster 5 spike changes were associated with a more than threefold decrease in "neutralisation titres" in people inoculated 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 neutralising antibodies in a proportion of convalescent COVID-19 people", the researchers concluded.
Furthermore, the SSI said that the virus had continued to evolve rapidly in the mink population, which boded further problems for tackling the outbreak.
"Following the Cluster 5 discovery, a mink-associated SARS-CoV-2 variant with six spike protein changes appeared", the SSI explained. "Hereby, the virus continued to acquire spike protein changes through its passage in mink".
Krause emphasised that this continuing evolution made the development in mink extremely worrisome.
Yet, contrary to the government's chain of actions, the SSI didn't recommend a total cull of farmed animals, instead advising that the infection be closely monitored, controlled, and limited.
Denmark's entire mink stock of 15 million animals was killed at the end of 2020. The nation's parliament has since made it illegal to keep mink in Denmark until 2022, raising questions about the future of a lucrative business in a world-leading fur trader nation.
The hasty cull has sparked numerous problems, including compensation to the farmers, who lost their subsistence, as well as morbid moments, including bloated mink corpses pushing their way up from shallow graves, and the authorities deciding to exhume and cremate them, lest they should contaminate the ground water.
Denmark has fully vaccinated some 31% of its 5.8 million-strong population.