In some ways, the approach to rabies vaccine is easy. In other ways, it’s complicated. To some degree, the medicine is easy, but other considerations (like regulatory requirements) cloud the picture.

The medicine:

Rabies vaccines are highly effective. A single initial dose provides at least 1 year of protection. The first dose is supposed to be given at 12 or 16 weeks (depending on the jurisdiction – rabies vaccines in Canada are labelled for use in dogs and cats 12 weeks of age and older), with a booster one year later. Getting that first shot is critical, so the animal is protected as soon as possible against this deadly – and zoonotic – disease.

After that, we can use 1 yr or 3 yr vaccines.

• For a 1-year vaccine product, if the animal is overdue, we’d just give another dose as soon as possible, but the yearly cycle does not change.
• For a 3-year vaccine product, after the initial dose and the first 1-year booster, the animal can safely go 3 years between boosters.  However, if the 1-year booster is missed, then we’d have to restart that primary series to stick to the manufacturer’s instructions, meaning the late booster would only be considered good for a year. Then we’d go to every 3 years after the next dose a year later. If the animal misses any of its 3-year boosters, the same would apply, i.e it would need a booster a year later to get back on the 3-year schedule.
• Note: As of March 2019, there is only one 1-year rabies vaccine product for cats still available in Canada, and none for dogs; all other rabies vaccines for dogs and cats in Canada are 3-year products.

That’s all pretty straightforward and by-the-book (or label, in this case).

The challenge is what constitutes “late.” Strict interpretation of the label would be that even a single day overdue would require the primary series to be repeated. Many would consider that overkill since rabies vaccines are so highly effective. However, there’s not much appetite for guessing when it comes to rabies. Once an animal is more than a couple of months overdue, it’s harder to say that the booster should count as a 3-year dose, since we’re deviating ever more from the label recommendations. So, prudence would dictate we go back to the start. If there’s concern that the provincial/state/regional authorities (especially border authorities) would use a strict interpretation and consider any lapse an indication that the vaccination series had to be restarted, then it’s safer to be more conservative and do that in your practice as well. More on that below).

From a rabies protection standpoint, I don’t worry about late vaccines (within reason) since rabies vaccines are so good, especially in an animal that has received multiple doses over the course of its life.

The “other considerations”:

What makes rabies vaccination delays complicated is most often regulatory/public health rules and interpretations thereof. In many areas, rabies vaccination is required by law; for example, in Ontario, all dogs, cats and ferrets over 12 weeks of age are legally required to be kept up-to-date on rabies vaccination, regardless of whether they have indoor or outdoor lifestyle.  I doubt there would be a fine applied in most cases for reasonable delays in vaccinating a pet due to COVID-19 restrictions over the last year (but each jurisdiction is its own…). However, the bigger issue is the response to a potential rabies exposure in such an overdue animal. When an dog or cat is exposed to a rabid (tested) or potentially rabid (untested suspicious) animal, the response depends on the pet’s rabies vaccination status. That response varies a bit by region; some default directly to the guidelines in the NASPHV Rabies Compendium, some adapt those guidelines, and others are… well, a bit unpredictable.

In Ontario, the response could range from simple observation with no strict confinement (e.g. a fully vaccinated pet that gets a booster within 7 days of the encounter) to a strict 6 month confinement (e.g. an unvaccinated pet that does not get a rabies vaccine within 7 days of the encounter). Animals with a history of lapsed vaccination are dealt with on a case-by-case basis, with things such as the time since the last dose and the number of lifetime doses being considered (among other factors). The pet could ultimately be treated as fully vaccinated or unvaccinated, depending on the details, and that can be the difference between life-and-death, as euthanasia is sometimes elected by owners in lieu of having to strictly quarantine the pet.

Understanding how your region addresses overdue vaccination is useful, to determine how strict you need to be about getting animals in for their boosters. If they’re not flexible and consider an animal’s vaccination status to be lapsed the minute they pass the 1- or 3-year mark, then we need to make sure we’re prioritizing rabies vaccinations so there are no gaps.

As an example, here’s the situation in my household:

• My dog, Merlin, has had multiple doses of rabies vaccine and is probably effectively protected for life. Him being overdue is probably low risk, but I wouldn’t want to let it go very far. I’d booster him when feasible but not stress about it, and would keep him on the 3-year cycle. If he’s not too far overdue, I’d have a strong case to consider him completely protected if he tangles with a rabies suspect.
• My cat, Milo, is less than a year old and has had a single dose or rabies vaccine. He’s higher priority to get boostered. If I miss the 1-year booster by much, I’d have to consider re-starting the primary series again, which means I’d give him a dose, and then another in 1 year, before switching to every three years. (That’s a picture of him… he doesn’t look very stressed about it).
• The outdoor cats (Rumple and Alice)  have received multiple doses or rabies vaccine over their lifetimes. They’re like Merlin, but higher priority for boosters since they likely have a greater risk of exposure to rabid animals.

The take home messages on rabies vaccination delays:

• Don’t let rabies vaccination lapse, if possible.
• I’d prioritize pets for rabies vaccination in this order
  • Animals that may have been exposed to rabies in the last 7 days because of an encounter with a suspicious animal that couldn’t be tested for rabies (or that was tested and was confirmed to be rabid.  This is a medical urgency.
  • Animals that have never been vaccinated for rabies (or unknown if they’ve ever been vaccinated). They need a dose ASAP to make sure they’re protected and won’t have to risk a long confinement period if they’re exposed to rabies.
  • Animals that have only had one dose of rabies vaccine in their lifetime.
  • Animals that are significantly overdue for their rabies booster (more than a couple of months).
  • Other pets that are due for a rabies booster (if there’s really a need to prioritize further, focus on dogs/cats that go outside unsupervised).