That may seem like a strange question, but bear with me and read on.
Mink are back in the news, mainly with respect to vaccination. Mink are very susceptible to SARS-CoV-2 and can transmit the virus back to people. Perhaps more concerningly, they can be the source of mutant strains, since more transmission (especially with a species jump) means more risk of mutation.
The question of vaccinating mink keeps coming up, and efforts to develop vaccines are underway. I’m no vaccinologist, so keep that in mind as you read this.
Vaccines can be used for different things, but I’ll focus on two broad categories
- Reduce/eliminate disease
- Reduce/eliminate infection
There are important differences.
Ideally we want a sterilizing vaccine, which prevents infection. That means when the virus encounters a vaccinated individual, it doesn’t do anything. It can’t establish an infection.
- Most vaccines aren’t that good. They can reduce the likelihood of disease or severity of disease, but the virus can still commonly infect.
- That might be fine, since the goal is usually to reduce illness.
- However, if those infected but somewhat protected individuals can still be infected and transmit the virus, it’s not great for disease control.
But even if a vaccine isn’t great, it can’t hurt, right?
- That’s not clear. There are a couple potential concerns.
Maintaining a reservoir
If a vaccine just reduces disease but not infection, that’s good for the individual mink, but could be bad for us. It would mean the mink are still susceptible to infection (introduced by people) and if the virus spreads widely and silently on the farm, it’s hard to detect and control. That means farms could be more likely to be silent reservoirs.
Further, the more a virus spreads and replicates, the greater the risk of mutation. Mutations are random events, but with more transmission, there’s a greater risk that these random events can occur. If a mutation results in increased transmissibility, increased virulence or poorer vaccine effectiveness, and that strain spread back into people, that’s obviously bad.
Encouraging vaccine resistant mutants
A vaccine that’s only marginally effective might help select for vaccine resistant mutants. The big concern with that is if those vaccine resistant mutant strains are also resistant to human vaccines, and they get into people. We don’t know if this is an issue but it’s been raised in the context of people with suboptimal immunity from only receiving a single vaccine dose.
I’m not saying don’t vaccinate mink.
- It might be a useful control tool (for mink and people).
- Don’t think about vaccination as the main control measure for SARS-CoV-2 infections in mink. It can’t be done in lieu of other infection control practices.
- Consider (and investigate) potential unintended consequences
- Don’t rush a crappy vaccine on basis of ‘it can’t hurt’ , since maybe it can.
If it’s going to be done, we need to make sure it’s done right. Cheap, rushed, suboptimal vaccines might make things worse. There are enough examples of pretty useless vaccines for animals that are on the market, so it’s a realistic issue. Conditional licencing of animal vaccines usually doesn’t require much data beyond indicating it’s unlikely to be harmful.
The best way to prevent issues in mink is to reduce this virus in people.
The next best way is to make sure infected people stay away from mink….better infection control practices (or fewer captive mink).