When an unvaccinated person is exposed to rabies, they typically receive post-exposure prophylaxis (PEP) consisting of a dose of anti-rabies antibodies and four (4) rabies vaccines over the course of two weeks. In dogs and cats, it’s a different story. We don’t use formal PEP protocols in pets in most regions.

  • Why not? I’m not sure. Probably because nobody has put that much effort into figuring out whether it would be effective (and it’s not an easy – or cheap – thing to study).

Texas has approached rabies exposure of domestic animals somewhat differently than the rest of the US, particularly when it comes to unvaccinated animals. If an unvaccinated domestic animal is exposed to a rabid animal, they can undergo a PEP regimen consisting of immediate vaccination, followed by a 90 day confinement period with additional rabies vaccine boosters in the 3rd and 8th week of confinement. This is in contrast to most other jurisdictions, where the two options are most commonly euthanasia or a single vaccine dose followed by a 3-6 month quarantine.

Texas also does a really good job of publishing data on their rabies response and control programs in domestic animals, so others can learn from the information. Their most recent publication (Wilson et al, J Am Vet Med Assoc 2024) reports on 1218 unvaccinated animals that underwent the Texas PEP protocol after possible exposure to a confirmed rabid animal between 2010-2019. The animals included 570 dogs, 138 cats, 347 cattle, 93 horses, and a smattering of other species. One cat and two previously unvaccinated dogs (that received PEP) went on to develop rabies.

  • That’s a pretty impressive 99.8% success rate, but we have to temper that a bit. We can’t say the Texas protocol is 99.8% effective overall, since it’s pretty certain that not all potentially exposed animals were actually exposed to the rabies virus. Only 22% of animals that underwent PEP had “direct exposure” to the rabid animal. Another 30% had “probable exposure” and 48% had “low probability” exposures (see table below). Almost half of the low probability exposures were cattle, since sometimes whole herds were managed as “exposed” when a rabid animal was found on the property.

We always err on the side of caution with rabies, and lots of low risk or unknown circumstances get called potential exposure to make sure we don’t miss any relevant exposures.

  • If we just include high risk exposures, the success rate drops to 91% for cats, but stays high at 99.7% for dogs, but it’s possible that even some of those were not true exposures.
  • So, it’s hard to put any type of accurate number on the success rate, but we can reasonably assume that the risk of developing rabies when this protocol is applied is low.

Looking at the PEP “failures” is also important, and in this case it’s a actually a bit of a good news scenario:

  • All 3 PEP failures were in animals less than 12 weeks of age. We don’t normally start rabies vaccination until 12 weeks of age because that’s the age that we know that it will work. In younger animals, there’s the potential that lingering antibodies inherited from the dam can interfere with response to vaccination.
  • Two of the three PEP failures only got their initial vaccine dose (see table below).
    • One dog died before the time of the dose in the 3rd week.
    • One dog just didn’t get its second dose for some reason, and died 31 days after exposure.
    • The cat got a 2nd dose, but signs of rabies developed the next day, so that dose was obviously too late.
  • It’s quite possible that these 3 PEP failures were animals that had no ability to respond effectively to a vaccine based on their age, and the onset of disease was quick enough that they didn’t get a chance to have multiple doses of vaccine during their confinement period.
  • No dogs or cats that were over 12 weeks of age and no dogs or cats that underwent the full PEP regimen got rabies.

Take home messages

Rabies PEP should be considered in domestic animals. There’s no guarantee that it can prevent rabies in an exposed dog or cat, but odds of rabies developing while being managed using this approach appears to be really low.

We can also flag the cases that are of greater risk of PEP “failure” (in this case, young animals that started PEP before 12 weeks of age).

I wonder whether the 3 and 8 week booster timing is too late. If we’re going to give multiple doses and we don’t have the option for anti-rabies antibody, why not approach it more like they do in people: give the vaccine ASAP (which is already part of the protocol), and then on days 3, 7 and 14? I can’t see any reason not to use that type of approach if it could possibly help avoid PEP failures.

Vaccine failures

One “true pre-exposure vaccination failure” was reported, which is an important case to note.

  • It was in a 3-year-old dog that was initially vaccinated at 16 months of age and got a booster 1.4 years later, meaning it was properly vaccinated and not due for a booster at the time it was exposed to rabies. Nonetheless the dog developed rabies and died.
  • On one hand, it’s just one case. That’s great. Rabies vaccine is one of the best vaccines we have. But no vaccine is ever going to be 100% effective, since we can’t guarantee that every animal will respond to a vaccine the way we want them to.
  • This is a reminder that while rabies vaccination is really useful and really important, we can’t dismiss the potential for rabies in a vaccinated dog or cat. It’s just really unlikely.

Two other previously vaccinated dogs also developed rabies. Both dogs were overdue for vaccination, so they are not considered true vaccine failures, but they’re also important to note.

  • One was a 7-year-old dog that was overdue following a 3-year vaccine (last dose given 5 years earlier). I’d really like to know if this dog had multiple vaccines before the age of 2, or just one dose, since I expect pretty solid, long-lasting immunity with a couple doses – but this also illustrates why you can’t rely on that in all dogs, and regular revaccination remains important.
  • The other case was a 2-year-old dog that had received a rabies vaccine as a puppy but did not get the 1-year booster.

The conclusion of the report was “Results indicated that this protocol is a viable option for unvaccinated domestic animals exposed to rabies. Alternative protocols warrant additional consideration.”

I think that’s a fair evaluation. We don’t really know how well PEP works in domestic animals, but it’s likely quite effective. It is certainly much better than doing nothing, and should be an option for exposed animals. However, I’d like to see a more aggressive PEP regimen than those currently used.

On a closing note, we don’t need to worry about PEP regimens for unvaccinated animals if we don’t have unvaccinated animals. All dogs and cats in rabies endemic areas should be vaccinated from 12 weeks of age and up. We’ll still see exposures in animals younger than that, but maximizing vaccination in animals that can be vaccinated is critical.