A recent paper about rabies post-exposure treatment in animals (Wilson et al, J Am Vet Med Assoc 2010) also contained some interesting information about rabies vaccine failure in pets. The study, which looked at data from more than 1000 animals in Texas from 2000-2009, mentioned a vaccinated 15-month-old cat that developed rabies. It had been vaccinated at 5 months of age and was not yet due for a booster, which would have been required at 17 months of age.
Rabies was also diagnosed in a dog and cat that had been vaccinated but were overdue for their boosters. Both initially received one dose of a 3-year vaccine, but they did not received the booster that is supposed to be given 1 year later. (Even with 3-year vaccines, pets are supposed to be given their first booster (i.e. their second dose of vaccine) after 1 year, before moving to getting boosters every 3 years). The dog was vaccinated 2 years and 9 months earlier. Twelve days after being exposed to a rabid skunk it was given a booster, but it developed rabies nonetheless and died 8 days later. The cat was vaccinated 2 years and 3 months earlier. It apparently did not receive a booster after it was exposed to rabies, and subsequently also died of rabies.
Another six dogs and three cats that were vaccinated developed rabies, but all of these were overdue for their booster or had been vaccinated less than 30 days before rabies exposure. These were therefore not considered vaccine failures.
This information should not be taken as an indication that rabies vaccination is not useful or that current vaccination protocols are inadequate. This involves a very small number of animals, and only one that was properly vaccinated. Rather, it should be a reminder that vaccination is not infallible and that the possibility of rabies cannot be summarily dismissed just because the animal has been properly vaccinated.