Canada recently lost its measles-free status, in large part because of a slip in our overall vaccination rate. A lot of that has been driven by vaccine hesitancy. The resurgence of measles in people shows what can happen when we aren’t using one of our best control methods (vaccination) optimally.

Vaccine hesitancy is an issue in veterinary medicine too, and it’s probably increasing. There are known overlaps between vaccine hesitancy in humans and animals; people who are wary of or opposed to human vaccination often have similar approaches to vaccination of animals. It’s a complex issue, though, with many causes, and unfortunately pretty limited data.

• One study of people in the US (Motta et al. 2023) showed that 53% of respondents reported at least one component of hesitancy, i.e. expressing concern that veterinary vaccines may be unsafe (37%), ineffective (22%), or unnecessary (30%). We don’t have comparative data for Canada; my guess is it’s less prominent here, but still a significant issue.

Vaccines are highly effective disease control tools, in both human healthcare and veterinary medicine. They aren’t perfect, but they are critically important. They can range from useful aids to critical tools to essentially the only line of protection, depending on the vaccine and the disease. Without vaccines, pet life expectancy would be shorter: we’d lose a lot of young animals to preventable diseases. Veterinary care costs would also be higher. We’d probably have fewer people with pets because of these challenges, especially in urban areas where a lot of pets and pet contacts would mean a lot of disease transmission.

Why are people vaccine hesitant?

It’s critical to understand the reasons behind vaccine hesitancy to try to mitigate the problem.

• Some people have completely understandable and valid concerns.
• Some people fundamentally do not believe vaccines are safe or effective, and they will not trust anyone or anything that says otherwise.
• Some people may not really know why they are hesitant – they’re simply unsure.
• Internal conflicts can be part of the problem too, such as a person who is really worried about the cost of vaccines, but doesn’t want to admit it (openly or to themselves), and might therefore convince themselves that it’s safer not to vaccinate, to avoid feeling like they are compromising their pet’s health by not vaccinating.

Various other complex scenarios occur too. The bottom line is it’s complicated, and often unclear. That makes addressing vaccine hesitancy challenging.  

• If someone has trust issues, we can educate them all we want about vaccine efficacy and safety. It won’t matter.
• If they’re terrified that their dog is going to die from the vaccine because of something they read online, that’s a completely different scenario that requires a different approach.
• If cost is driving concerns, that’s harder to address.

There’s a lot more to discuss about reasons for vaccine hesitancy, but I’ll hold off on that for now. My focus today is on the implications of vaccine hesitancy.

Potential impacts of moderate decreases in vaccine coverage

Less vaccination means more disease at the individual level. It can also increase the risk of outbreaks, increase the risk of well-controlled diseases becoming uncontrolled, and allow for re-introduction of diseases that were previously successfully contained.

For humans, we want really high measles vaccination rates (>95%) to prevent spread, as well as to protect individuals from disease. That way if someone happens to have measles, the risk of spread is low because so many people are already protected. We need a really high percentage of vaccinated people in the population for this to work for a highly transmissible virus like measles, but we were previously able to do that in Canada – until recently. As vaccine rates slip, when there is an introduction of measles virus into a population, there is a higher risk of sustained transmission among unprotected people, sometimes with devastating results.

It’s a bit different for dogs and cats. We don’t have the same level of baseline vaccine coverage for most of the diseases against which we vaccinate pets, and for some diseases, we also have feral and wildlife reservoirs.

Individual animal risk is straightforward, but population risks in pets are harder to understand. Those risks can’t be ignored, but they also shouldn’t be overstated, since we need to be transparent and clear in our communication with pet owners in order to maintain trust. Let’s use vaccination of dogs as an example:

Distemper

Canine distemper virus (a relative of measles virus) is one of our big concerns in dogs. Disease can be really severe, but vaccines are highly effective. However, we’re nowhere close to eradication because we still have a fairly large pool of unvaccinated dogs, and canine distemper virus is also endemic in wildlife in many areas (especially in raccoons). Reduced vaccination in dogs won’t lead to re-emergence of the disease, since it’s already endemic. Reduced vaccination will mean more disease in general.

So, the risks of less vaccination are mainly to the unvaccinated dogs. However, there is a spillover risk. Just like in humans, where we focus on vaccinating as many people as possible to protect those who can’t be vaccinated, the same principle applies in dogs, since some dogs cannot be vaccinated or cannot respond well to a vaccine. An unvaccinated dog that gets distemper poses a risk to those dogs. The more unvaccinated dogs, the greater the risk to puppies especially, and for a potentially devastating outbreak.

Parvovirus

Issues with parvo are pretty similar to those with distemper. It’s a potentially life-threatening disease in unvaccinated dogs. There’s low level but continual circulation of parvo in the dog population because there are enough unvaccinated dogs (domestic and stray) to maintain it. The risks of decreased vaccination are mainly to the unvaccinated animals. However, as with distemper, when there are more infected dogs, there’s more risk of transmission to other dogs, including puppies that are still to young to be vaccinated.

Leptospirosis

This is an important vaccine in many areas. Leptospirosis is a bacterial disease caused by the spread of Leptospira from wildlife reservoirs (e.g. raccoons, rats). We can’t eliminate lepto from wildlife, so reduced vaccination doesn’t change the overall risk of exposure, but it increases the risk to the unvaccinated dog.

However, there are some secondary risks here too. Dog-to-dog and dog-to-human transmission of lepto seem to be rare, but can happen. If a dog is unvaccinated, it’s at risk of severe disease, and that risk extends (at a low but non-zero level) to its canine and human contacts.

Rabies

There are a lot of interesting aspects to rabies when it comes to dogs. In North America, we don’t have the strain of rabies virus (canine variant) that circulates in dog populations in other countries. Dogs can still get rabies from wildlife reservoirs, such as bats, raccoons and skunks, but we don’t expect strains from those species to result in ongoing transmission of rabies within the dog population. However, canine variant rabies is highly prevalent in some parts of the world, where it causes most of the ~60,000 global human rabies deaths annually. We are at some risk of importing dogs carrying canine rabies. Despite the controls we have in place to prevent it, at least two rabid dogs have been imported into Ontario since 2021, and there’s ever-present risk of it happening again.

If a dog is not vaccinated against rabies, the main risk is to itself. If it tangles with a bat and is exposed to the virus, it’s more likely to develop rabies (which is essentially always fatal). There are other risks, though. When a dog has rabies, there is a short but important window of time when it can transmit the virus through its saliva to any human, domestic mammal or wild mammal contact. There can also be substantial healthcare costs for investigation of human exposures and treatment of exposed individuals. Unvaccinated dogs and cats that are potentially exposed to the virus can be at risk of developing rabies for months, necessitating long confinement periods to prevent exposure of even more people and animals (and sometimes pet are even euthanized because of the risk if they can’t be safely and effectively confined).

The broader population risk from decreased rabies vaccination is much lower. We have eradicated canine rabies in Canada and really don’t want it back. For that to happen, we’d have to import a dog with rabies, it would have to infect other dogs or wild canids, and they would have to keep infecting enough new dogs/canids to keep the disease cycle going. That’s not realistic in a controlled pet dog population, but is a concern with feral dogs (which we don’t have many of in most regions) and wild canids (which are very common in some areas).

The odds of canine rabies virus coming into the country, making it into wild canids and establishing itself anew are really, really low, but they are not zero. While the risk of an unvaccinated pet dog contributing to re-establishment of canine rabies in Canada are likewise exceptionally low, the implications were it to happen, both in terms of health (human and animal) and the costs for control are substantial. So it should not be ignored. Still, the main risks from a dog that is not vaccinated for rabies are to the unvaccinated dog itself and its close contacts.

“Kennel cough” (canine infectious respiratory disease complex, CIRDC)

When it comes to CIRDC, we mainly vaccinate dogs against Bordetella bronchiseptica and canine parainfluenza, with a smattering of vaccination against canine flu. These vaccines are meant to help reduce the risk of infection and reduce severity of illness when it occurs. They’re useful, but they’re mainly for individual health, not reducing transmission or containing the disease. These vaccines are also not as widely used as others, so overall vaccine coverage is pretty low. A moderate reduction in vaccination would not do too much to impact the broader epidemiology of this complex. It would mean that more dogs would get sick, or get sicker than they would have with vaccination.

Do I worry about vaccine hesitancy?

Yes. I hate to see animals dying of vaccine preventable diseases. We can’t prevent all disease, but by optimizing vaccination, we can maximize the benefits to vaccinated animals, and to some degree, other animals and people around them.

How do we address vaccine hesitancy?

That’s way more complex that I can cover in a few paragraphs, but I’ll highlight a few key aspects for addressing vaccine hesitancy (hard core anti-vaxxers and people who spread misinformation are a separate topic):

Communicate communicate communicate

• We have to listen to why people are hesitant.
• We have to acknowledge their concerns, even if we disagree.
• Sometimes we can educate.
• Sometimes we can work to provide more confidence in veterinary care or vaccines.
• Sometimes we can allay fears.
• Sometimes we can just have a good conversation, agree to disagree, and still work to care for the animal.
• …and unfortunately sometimes it falls apart, or views are so polarized that there’s no moving forward. We just hope those are the minority of cases.

We don’t have the exact same issues in veterinary medicine as human medicine, and approaches to vaccine hesitancy aren’t necessarily going to be identical, but vaccine hesitancy among animal owners is definitely a concern. We need to develop a better understanding of how common it is (and more importantly, the reasons for it), look at ways to address it (including how it’s done in human medicine), have open and honest discussions, and try to optimize vaccination. There’s no one-size-fits-all approach to vaccination and there’s no one-size-fits-all approach to a vaccine-hesitant owner.