(TL:DR… check out the TikTok version at the bottom)

When I was a newly graduated veterinarian in general practice, I gave puppies and kittens their first rabies vaccine at 16 weeks of age. That was the standard at the clinic and a common practice elsewhere. Now, if I ask audiences of veterinarians when they vaccinated against rabies, I’d say a majority still say 16 weeks.

But is waiting until 16 weeks to vaccinate against rabies a good approach?

When we vaccinate young animals, we’re aiming for the sweet spot of vaccinating them as young as possible, but at a time when we’re confident the vaccine will work. Antibodies that animals get from their mothers can interfere with vaccines, but those antibodies wane over time. We give a series of “core” vaccines (e.g. parvovirus and distemper virus in dogs) starting at a young age, knowing that they may not respond initially but eventually will, as maternal antibody interference disappears.

For core vaccines, we want to give at least one dose at 16+ weeks of age. However, rabies vaccine can be given earlier. Rabies vaccines in Canada are licensed for use at 12 weeks of age. In Ontario, the legal requirement is vaccination of all dogs and cats (and ferrets) against rabies at 3 months (12 weeks) of age.

So, why are puppies and kittens commonly vaccinated for rabies at 16 weeks?

The main reason is probably habit – “that’s what we’ve always done so that’s what we do.” Another reason is a focus on getting puppies and kittens back for that critical 16 week core vaccine. There’s concern that if people are fixated on the need for rabies vaccination for their pet, if they get it at 12 weeks, they may not be motivated to come back at 16 weeks, and therefore might put their pet at high risk of getting other serious disease like parvovirus or distemper.

12 weeks vs 16 weeks… what difference does 4 weeks make?

Most of the time, nothing, but sometimes, it’s life-and-death. Earlier vaccination means earlier protection from rabies. However, probably as importantly, earlier vaccination reduces the risk of significant isolation requirements if the animal is exposed to a potentially rabid animal.

For example, let’s say a 16 week old puppy was outside in the yard and night, and fought with an abnormal-acting raccoon. The puppy has some bite wounds, but the raccoon ran off and can’t be tested for rabies. This would typically be considered a potential rabies exposure.

Scenario 1: Puppy was vaccinated at 12 weeks of age. It’s been more than 28 days since the vaccine, so we’re quite confident it’s protected. In Ontario, that means we would give a booster vaccine within 7 days, and they there would be a 45 day observation period. That’s pretty minor and mainly means minimizing the animal’s contacts outside the household and keeping it on a leash when off the property.

Scenario 2: Puppy hasn’t yet been vaccinated (or was vaccinated so recently that it’s not considered protected). There are major implications here. If the puppy gets a rabies vaccine within 7 days, it gets a 3 month “precautionary confinement period” (basically, quarantine, but there are legal connotations to that word so government guidance avoids it). If a post-exposure vaccine isn’t given, the confinement period is extended to 6 months. This is a much bigger deal than Scenario 1 because it requires keeping the puppy at home at all times (unless medical attention is required), limiting contact to one age-appropriate caretaker, preventing contact with other people or animals, only going outside on a leash and in a fenced area (double barrier to escape) and keeping the puppy in a secure indoor area that allows the caretaker to observe the animal before direct contact and prevents accidental escape when indoors (for example, double door entry).  That’s tough to do with a puppy and sometimes, euthanasia is elected instead. Even if owners chose to proceed with confining the puppy, it can have a major impact on the puppy’s socialization and increase the risk of behavioural issues later in life.

So, from my standpoint (plus the legal requirement here), we want to vaccinate puppies and kittens as close to 12 weeks as possible. It’s rare that a 4 week delay would cause a problem, but when it does it can be major. We also want to make sure that doesn’t result in puppies and kittens failing to come back for that critical 16 week core vaccine, but we can educate owners about the need for that.