Warning: Distressing images
It was the news virologists have been dreading.
Ever since the Chinese authorities released the full genetic code of Sars-CoV-2 in January, scientists have closely monitored any hint that the virus was mutating.
This is because a genetically stable virus presents a stationary target at which the hundreds of teams feverishly developing a vaccine can take aim. It also confers immunity from reinfection on those who have fallen ill with the disease, albeit probably not permanently.
The virus rampaged around the world, killing more than a million and paralysing economies. Yet, in this one respect at least, all seemed well.
Variations were discovered, but overall the genetic code of the virus remained largely consistent, strengthening hopes that a vaccine or vaccines could, if not eradicate the disease, suppress it to an extent that would allow a substantial return to normal life.
The news from Denmark threatens to change all that.
Among the mink farms of the North Jutland and Zealand regions, the virus has been rampant, spreading from humans to the furry farmed animals, then back into their handlers and the surrounding populations. Experts have now found that, as the virus hopped from one species to another and back, it has significantly mutated.
So far, they have identified five clusters of variations to its genetic code. Crucially, some of these affect the all-important spike protein, which viruses use to penetrate cells. It is also the protein against which humans develop antibodies - through vaccination or prior infection - to fight off infection.
Danish scientists have known about the mutations for months, but it is only this week that results from laboratory analysis revealed their sinister potential. They indicate that antibodies are less protective against these new strains of Sars-CoV-2.
The crisis was expressed in stark terms by Jeppe Kofod, the Danish foreign minister, yesterday.
"We have indications that this unique mutation has reduced response to antibodies, which can ultimately affect the efficiency of potential vaccines," he said. "I cannot underline enough how seriously the Danish government takes the situation."
Scientists do not believe that the new strains are any more dangerous or contagious. But they fear the prospect of the significant spread of a strain that the vaccines under development are powerless to suppress. It would take many months to design, test and develop a supplementary vaccine.
The news from Denmark broke as a study by Glasgow University identified another strain, named N439K, which may also be capable of sidestepping antibodies. It was discovered in Scotland in March, when it infected 500 people, later emerging in Romania and now observed in 12 countries, including Norway, Germany and the US.
In a desperate attempt to contain the Danish outbreaks, all 17 million mink in the country are now being culled. People entering Britain from the country must now quarantine for two weeks. More than 200 people have since tested positive for one of the variants in Denmark, 12 of whom had the so-called "cluster five" variant, which appears not to trigger an immune response.
Overall, the mink variants were detected in 40 per cent of samples of people testing positive in North Jutland.
Statens Serum Institut, one of the country's largest public health research bodies, has been arguing for months that failing to order a cull of minks presented a "major risk to public health".
Tyra Grove Krause, of the institute, said: "This may mean that in the future some of the Covid-19 spike-directed vaccines may be less effective against these variants of the virus."