Denmark is one of the largest mink producing countries in the world, and mink on numerous farms have been infected with SARS-CoV-2 from farm workers with COVID-19. At last report, 216 farms were affected. That wasn’t too surprising since outbreaks on mink farms have been seen in several countries, with particularly widespread infection on farms in the Netherlands. The issue is a recent report by the Serum Statens Institute (SSI) and some government releases about emerging “mink strains” of SARS-CoV-2 and a large number of human infections with a “mink strain.”

Crap.  Mutated virus. That sounds bad.

Not necessarily. Viruses mutate all the time. It’s a random event. It’s more likely to occur when there are large numbers of infected individuals, simply because there are then more opportunities for random mutation. A mink farm with thousands of closely housed and highly susceptible mink is a great place for that. It’s also probably more likely when a virus moves between species, as some random mutations might make it easier for the virus to infect their new host species.

So, what’s going on with SARS-CoV-2 in mink in Denmark?

At this point, five different variant strains of the virus have been found in mink, which include variations in the spike protein the virus uses to attach to (and subsequently infect) cells. If such a mutation makes it easier for the virus to attach to cells of a given species, it becomes more infectious to that species. Conversely, if a mutation decreases the ability of the virus to attach to cells, it makes the virus less infectious. The spike protein is also an important vaccine target, raising some concerns about whether mutations could decrease the effectiveness of some vaccines that are being developed (a bit more on that below).

One particular variant has been found in human samples too, some from people that are connected to the mink farms, and some from people who aren’t.  The variant strain has been found in 214/5102 virus isolates from people, 94% of whom are in North Jutland, where most of the infected mink farms are. This variant accounted for 40% of the isolates in that area, which is pretty impressive (not in a good way).

A translation of the Danish SSI report about the emergence of these variants in mink and their spread to the human population says “SSI estimated that continued mink breeding would entail a significant risk of recurrence of a large spread of infection among mink and humans, as seen in Western Denmark in 2020. SSI estimated that this would pose a major risk to public health. Both know that the many infected mink farms can lead to a greater disease burden among humans, and know that a large virus reservoir in mink increases the risk of new virus mutations occurring again, which vaccines may not provide optimal protection against. Overall, the immunity gained through vaccination or past infection may also be at risk of being weakened or absent. The overall conclusion, which was also supported by the Danish Health and Medicines Authority, was therefore that continued mink breeding during an ongoing COVID-19 epidemic entails a significant risk to public health. Including the possibilities for optimally preventing COVID-19 with vaccines.”

Is this really a “mink strain” of SARS-CoV-2?

It’s hard to say. It’s a strain that has been found in mink. It might have mutated in them or it might have mutated in the person that infected them. Most likely, it did evolve in the mink, spread to people, and then those people spread it to other people.  Everyone’s talking about it like it’s one strain, but there are actually several strains linked to mink now. One is getting the most attention, though.

How did hundreds of people get infected with this strain? Are mink everywhere in Denmark?

No, mink aren’t everywhere, but people are. This is a situation where (I assume) most of the transmission is still human-to-human. It came from people, probably changed in the process of being transmitted between so many mink and then was likely transmitted back to a few people with close contact with the mink, and is now back to being transmitted widely between people.

So, why do we care?

  • Anytime we see movement of a virus into another species, it’s a concern. Mink infecting people isn’t the real problem, since few people have any direct contact with mink. The issue is whether mink can complicate overall control of the disease in people. More species involved means more problems to address. Denmark was already culling affected and neighbouring farms, but as more mink farms get infected, that creates more opportunities for new strains to emerge.  So they’ve now made the difficult decision to cull all farmed mink in Denmark until the COVID-19 pandemic in people is under control.
  • Related to the above, the last thing we want is this virus in wildlife. Transmission to cats has been found on mink farms in the Netherlands, Fortunately, so far, we haven’t seen issues with SARS-CoV-2 infection in wildlife (but we didn’t see issues with mink either until we suddenly had a big issue with mink… if you catch my drift). Mink create a potential bridge to other species, and we don’t want that.

And the big one….

  • Is this mutation a problem for people? Early lab data suggest that this virus isn’t neutralized as well by antibodies from people infected with the more common strains found in the human population. That could impact the effectiveness of antibody-based treatments or vaccines, but it’s too early to say there’s a relevant issue. It’s certainly something that needs to be investigated as if it’s relevant. If it impacts vaccination, we start getting into a situation where we might need a vaccine that protects against multiple strains of SARS-CoV-2 (and none of the billions of dollars in vaccine development money has been spent looking at this new strain).

Some new outlets have talked about the chance for a “new pandemic.” Is that realistic?

No. Our current pandemic is doing just fine and isn’t going to be displaced. We are effectively transmitting the original virus between people, and we will probably effectively transmit this other strain too. It’s not likely to change the character of the pandemic (unless it impacts treatment or prevention). There’s no evidence that it causes more serious disease.

What does this mean in the big picture?

It’s too early to say. Whether this is an academic curiosity, a mutation that might lead to some interesting epidemiological data but has no additional health impact, or is a sign of a looming problem, is hard to say.

What do we do?

  • Relax.
  • Avoid kissing mink (most mink would eat your face if you tried, anyway).
  • Continue to pay attention to animals as potential sources of infection.
  • Most importantly: control human-to-human spread. The best way to prevent the spread of mink-strain COVID-19 is to prevent spread of COVID-19. Period.

In the big picture (jumping on my soapbox for a moment), this is why I’ve been saying these things since January. It’s why we criticized groups like CDC that said “there’s no evidence animals can be infected” before there was any effort to find out. We need to approach emerging diseases proactively, by looking for potential problems and taking steps to control them early, rather than waiting for definitive evidence of a problem.

Photo by Markus Winkler on Unsplash.