Concerns about animal aspects of the COVID-19 pandemic come in waves. Most of the time they are ignored or dismissed, then there are periodic flurries of attention and (often over-) reaction.
Questions about vaccination of animals follow a similar pattern and have been on the rise lately.
So, should be we lining up domestic and wild animals for vaccination?
- Yes, no and maybe…but mainly no.
To properly assess this question, we need to step back and think about what vaccines can potentially do.
There are 4 main areas I think about when considering whether vaccination may be useful.
- Prevention of disease:
- In reality, this is ‘prevention of severe disease’. If a species doesn’t get very sick and just has mild, transient illness, there’s little animal health value of vaccinating those from this standpoint.
- Prevention of transmission to people:
- This has been documented for a few species but not many. Most transmission is human-to-animal and animals are most often dead end hosts (e.g. if my cat gets infected, he got it from someone in my household and is unlikely to spread it any further)
- Prevention of transmission to other animals:
- Can the animal be spread it to other animals of the same species of be a bridge, spreading the virus to other wild or domestic animals?
- Prevention of establishment of a reservoir where new variants could emerge:
- This is the big concern about animals. It requires a highly susceptible species with a large population of animals that have frequent and close contact, to allow for longterm, continued transmission of SARS-CoV-2
Not many species check many (or any) of those boxes.
The other thing to consider is what vaccines might actually be able to do. We have very little information about vaccines for animals. They’re based on older technology than our human mRNA vaccines and those techniques haven’t been known to be able to produce highly effective coronavirus vaccines in the past. Vaccine science is improving and I’m not bashing the vaccines or the companies (I’m grateful they’re working on them). But, I’m realistic.
Vaccines can target a few goals:
- Reduction of severe disease
- Reduction of disease
- Reduction of infection (with or without disease)
- Prevention of infection (sterilizing immunity)
We don’t know how well animal vaccines do those in different species (and, based on what we know about the more technologically advanced human vaccines, reduction of severe disease is likely a much more realistic target than reduction of transmission).
Another issue is the vaccine coverage that would be needed. If we’re targeting vaccination as a tool to reduce establishment of the virus in wildlife, we need a vaccine that significantly reduces infection and transmission AND we need to vaccinate a large percentage of the population (and keep doing that, since population turnover is high in many wildlife species).
We also don’t know how long immunity persists or how it holds out with different variants.
Once we start thinking about all these requirements, I think it shows that vaccination is currently going to be limited to a few niche situations.
- They commonly get infected, but rarely get seriously ill. They are rarely going to be the source of infection (they are infected by their owners).
- Cats and dogs also don’t live in large groups where virus transmission can be sustained longterm for a reservoir and source of variants.
- Indoor-outdoor cats are more of a risk as a bridge between infected households and other people or animals, but odds of a significant role in transmission are fairly low AND any effect on this would require a vaccine that prevents infection and virus shedding.
- I’m glad we have vaccines ready in case something changes and we get a strain that causes more serious disease in dogs/cats, but I can’t see a use for vaccination now.
- Mink check a few of those boxes, as a species that is susceptible, can get sick, that is housed in large populations, that has been shown to develop new variants and that can spread the virus to people and other species.
- Vaccination of all mink on a farm is also possible.
- Vaccination is probably a more effective tool for mink health than public health, given the questions above about whether vaccines actually reduce transmission. If they just reduce disease but allow for transmission (or transmission that’s not noticed because the mink stay healthy) then it might not be useful or might even be counterproductive.
- Here’s where there’s the most potential. Some zoo species are highly susceptible and can die from infection with this virus. These animals can be valuable emotionally and economically, and from a conservation standpoint. So, more zoos are vaccinating their non-human primates (e.g. apes) and cats. Some are also vaccinating their mustelids (mink family…some, like the black footed ferret are endangered species) and cervids (deer family, since we know some deer species can spread the virus).
- They check a few of those boxes above, as they are highly susceptible and may be able to maintain circulation of the virus, leading to new ‘deer’ variants. So, there’s reason to think about vaccinating them.
- However, this requires a vaccine that significantly reduces infection and transmission (and I’m not very confident we have that).
- It also requires vaccination of a LOT of animals. If we need to vaccinate 80% of deer, for example…well…..good luck.
- Further, lots of new deer are born every year so this would have to be continued until SARS-CoV-2 is out of circulation in deer or people. That doesn’t seem very practical to me. Rabies vaccination of some wildlife species is used here and it’s highly effective. However, that’s a highly effective vaccine that can be delivered through baits that can eventually cover a pretty high percentage of the target population. That’s going to be tough to do.
We’re not going to vaccinate our way out of animal issues with this virus. We need to control SARS-CoV-2 in humans to have any hope of controlling SARS-CoV-2 in animals. Vaccine research is important so that we can have vaccines available should opportunities be identified and continued vaccine development may get us to the point where we have a highly effective vaccine that stops transmission. However, without that, the potential impact of vaccination of most animals is limited.