Dear Doctor: Vaccine Confusion


Q I asked a receptionist at my vet’s office if she knew about the 3-year schedule for vaccines and why they still give annual shots. She told me that there are two different strengths, and they prefer to give the less potent one annually. Have you heard of this — two different strengths for vaccines?

Charell Johnston

Shelton, Washington

Dear Ms. Johnston,

A There aren’t two different strengths of any of the vaccines. Some need to be boostered annually, and some can be given every three years.

The ones that need to be administered annually are those inoculations against such illnesses as Lyme disease, influenza (flu), and leptospirosis, which can cause life-threatening infections of the liver and kidneys. All of these are considered non-core vaccines, which means not all dogs need them. They are recommended for dogs based on certain risk factors, like environment and lifestyle.

For instance, the pathogen that causes Lyme disease is found throughout the Northeast but not in all areas of the country. It’s the same for leptospirosis, which can occur in areas of dense wildlife, livestock, and rodents, since it’s spread through the infected urine of these animals. Not all dogs are at high risk for the flu, either, especially if they tend not to hang out with other dogs at dog parks, dog shows, groomers, boarding facilities, or doggie daycare.

If any of the non-core vaccines is called for, the reason it’s given once a year rather than every three years is not because of a lack of potency. It’s “because of the way the body ‘remembers’ the vaccine,” says Heather Loenser, DVM, the American Animal Hospital Association’s Veterinary Advisor for Public and Professional Affairs. “Immunity or ‘memory’ lasts for about a year against Borrelia burgdorferi ( the bacteria that causes Lyme disease), Bordetella (“kennel cough”), Influenza, and Leptospira. Local law governs how often a dog must be vaccinated for rabies, varying from one to three years.”

Shots against diseases such as distemper and parvovirus come as combination vaccines and are considered core because they’re meant for all dogs. They can be given every three years because the levels of antibodies to these diseases remain elevated in dogs longer after the inoculations are administered; their bodies have a longer lasting “memory” for them.

Your veterinarian can help you determine which vaccines your dog might need. For more information, see the American Animal Hospital Association’s recently released vaccination guidelines at


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