Senior dog getting a vaccination
I hear this question a lot in my practice, and it’s a good one: Does my senior dog or cat still need vaccinations? As with so many things in veterinary medicine, it depends.

Some pet owners tend to think of parvo and distemper in dogs and feline panleukopenia, calicivirus and herpesvirus in cats as diseases that only affect puppies and kittens. By the time our pets are 8, 10 or 12 years — or older — they should have been vaccinated for these diseases several times in their lives: the first few times as puppies or kittens, a booster at one year and then boosters every three years, as recommended by the American Animal Hospital Association and the American Association of Feline Practitioners. So how likely is it that they are going to get one of these diseases in their golden years?

The short answer is that older pets have little risk of developing these infectious diseases if they were effectively vaccinated as puppies or kittens and developed an immune response. But that doesn’t mean there is no risk to an older pet.

Why Vaccinations Are Important for Older Pets

In rare instances, a vaccinated animal doesn’t develop an immune response to the specific disease. My colleague Ronald Schultz, DVM, PhD, an immunology expert at the University of Wisconsin, says about 1 in 1,000 dogs won’t develop immunity to parvo, for example, and about 1 in 5,000 won’t develop immunity to distemper. Genetics play a key role in whether a pet responds to a vaccine and whether he develops an adverse reaction to it.

Another thing to consider is that a senior pet’s immune system is no longer at its strongest. Like so many other things, the immune system’s effectiveness diminishes with age. (The $5 term for this decline is immunosenescence.) A pet may be more at risk of infection in old age and less able to fight one off.

The type of vaccine is also a factor. While the core vaccines — parvo, distemper, adenovirus and most types of rabies vaccines — have been shown to be protective for a minimum of three years (and, in some cases, for seven or more years), noncore, or optional, vaccines for bacterial diseases such as bordetella or leptospirosis don’t provide long-term immunity and may need to be administered annually if your pet is at risk for those diseases.  If these noncore vaccines are not given annually, immunity is lost. Dr. Schultz says pets who haven’t been vaccinated annually for these types of diseases should receive two doses of vaccine two to four weeks apart, just as they did when they received the initial vaccination.

Keeping senior pets immunized can help protect them from disease, but like any medical procedure, vaccinations aren’t without risk. Reactions to them are rare, but they can happen. If you are concerned about giving vaccines because your pet is old, has a chronic disease or has had reactions to vaccines in the past, talk to your veterinarian about a titer test for parvo, distemper and adenovirus in dogs and panleukopenia in cats to check immune response. If he has adequate levels of antibodies to distemper, parvo or adenovirus, he’s immune. If he doesn’t have detectible antibodies to disease, he should be revaccinated. Titer testing can be done every three years to check your senior pet’s level of antibodies and help ensure that his immune system is still humming along.

More on Vetstreet: