Limited studies suggest that booster vaccinations for many of the core vaccinations last for at least seven years. Sometimes immunity lasts a lifetime. "We know that for [canine] distemper and parvo, for example, the immunity lasts a minimum of five years, probably seven to nine years, and for some individuals for a lifetime,” says veterinarian Jean Dodds. For cats, so far we have challenge data out nine years showing that immunity is still protective. Annual boosters for the core vaccinations are excessive for most dogs and cats. However, given the limited number of animals involved in these studies, three years seemed like a reasonable compromise. With the exception of rabies vaccine, the U.S. Department of Agriculture doesn’t require data beyond one year for any vaccine. What does all this mean for your dog or cat? As with many other aspects of veterinary medicine, vaccinations are becoming individualized, but in most cases, fewer and less frequent vaccinations are the way to go.