Here’s a question I often get: Why do pets have to be vaccinated every year for rabies? Is there really a medical reason for this, or is this regulatory overreaching at the expense of our pets?

After all, humans are often vaccinated only once for certain "bugs" and remain immune to the particular disease they cause for life. Why is it not the same for animals?

The main reason people ask this is because they’ve heard or read of negative reactions to rabies vaccines in some pets. They assume this product is less safe than they’re led to believe by veterinarians and regulatory agencies, and they’re worried for their pets––particularly those who might suffer from chronic conditions or at very low risk of actually coming across a rabies infected animal.

Truth be told, rabies vaccines are considered very safe. Nonetheless, the reality is uncomfortable: more pets actually die of the consequences of being vaccinated than come down with the virus.

Having said that, you might wonder how it’s possible for me, or any veterinarian, to defend the use of this vaccine. But if you think about it, this scary-sounding reality is likely the case with all successful vaccines. After all, the goal of a vaccine is to render a disease so rare that very few animals are ever even exposed to it.

For example: The side-effects of polio vaccination in humans are far more common than the disease itself. And yet we’d never advocate the elimination of the vaccine from our medical repertoire. That’s because the vaccine has managed to keep polio out of our population so successfully. Vaccination is therefore considered an "acceptable risk" to the individual, given the population’s overall protection.

Similarly, it remains the consensus of the human and veterinary medical communities alike that the benefits rabies vaccine confers to both human and animal populations outweigh the individual risk of vaccination.

On the plus side, yearly vaccination is no longer considered a medical necessity. Every three years is now considered sufficient. And this less stringent recommendation may well relax even more in years to come.

Consider, also, that while our government may require rabies vaccines every three years for the protection of public health, individual veterinarians may exempt some pets––temporarily, at least––on the basis of their compromised health.

It's also the case that testing for the presence of rabies antibodies with a simple blood test called a "rabies titer" is one approach to achieving exemption from additional, potentially unnecessary doses of vaccines in other countries. The U.S. does not yet recognize this test when it comes to replacing the requirement for vaccination.

That’s because the duration of immunity of rabies vaccination has not been completely and irrefutably established by the veterinary community. It’s also because measuring antibody levels through blood testing does not necessarily mean the animal is 100 percent immune to rabies. (Something called "cell immunity" is arguably as or more important than the number of antibodies the immune system brings to bear.)

Yes, it’s true that if your pet has already received a round or two of rabies vaccines, he or she is likely to be protected by antibodies against rabies for his or her entire lifetime. In fact, I received the human version of the rabies vaccine in 1991 and my own antibody levels are still quite high. So why force pets to undergo such frequent vaccines? Are they so biologically different?

Not at all. But you might choose to view things differently if your child were bitten by an animal that had been vaccinated only once ... ten years ago, for instance. In the absence of hard science on the subject, human health will always trump animal health in these matters.

Until veterinary science can prove that vaccines last longer than they do, your best bet in the interim is to play it as safe as you can. Make make sure your pet is healthy when vaccinated and only receives his or her rabies shot when administered by a trusted veterinarian whose selection, storage, and handling of the vaccine is likely to adhere to the highest standards of vaccine quality and safety.

Dr. Patty Khuly