In the past, dog owners vaccinated their pets for every disease, every year, and some veterinarians still recommend "annual boosters" for their patients. Research has shown, however, that immunity to viral diseases lasts far longer than one year. Vaccinations for bacterial diseases provide shorter-lasting immunity and may be required annually.
Core vs. Non-Core Vaccines
In 2003, the American Animal Hospital Association developed a set of guidelines for canine vaccinations. The guidelines introduced the concept of "core" vaccines—those that should be given to all dogs—and "non-core" vaccines—those that should be given only to dogs at risk of contracting the disease. Core vaccines include parvo, distemper, adenovirus and rabies; these vaccines are viral and after the initial series are given on a revaccination schedule of three years or longer. Rabies vaccination is mandated by law in most of the United States, and local laws might require you to revaccinate more often than every three years.
Bordatella (Kennel Cough)
The most common non-core vaccine is for Bordatella bronchiseptica, often called kennel cough. Kennel cough is actually a complex of symptoms, much like the human cold, and like a cold can be caused by a number of different bacteria or viruses. The Bordatella vaccine only immunizes for a few of these organisms, which is why vaccinated dogs might still come down with the disease. Bordatella shots are recommended annually for dogs that have frequent contact with other dogs, such as those going to dog shows or day care. Most boarding kennels require a recent Bordatella shot prior to admission. Some veterinarians recommend giving this shot every six months to at-risk dogs.
The Leptospirosis vaccine is thought to cause a high incidence of adverse effects, and the AAHA guidelines recommend it not be given to puppies prior to 12 weeks of age. Several subspecies, or serovars, of Lepto exist; the recommended vaccine protects again four of them, but there is little cross-protection to other serovars. Dogs at highest risk are those exposed to livestock or wild mammals; outbreaks peak during the rainy season, so at-risk dogs should be vaccinated annually in the late winter.
The bacteria that causes Lyme disease is transmitted by ticks, and owners of dogs who are exposed to ticks might consider vaccinating for Lyme disease. The vaccination is controversial, however; it may cause serious adverse effects, including a form of Lyme disease. Most infected dogs will not show any signs of Lyme disease; those that do typically respond very well to antibiotics. The Lyme vaccine does not protect against other tick-borne diseases, so tick control methods are still necessary for vaccinated dogs.
Canine influenza is caused by the H3N8 virus, and was first seen in dogs in 2004. A nationwide outbreak occurred in early 2009, and shortly thereafter a vaccine was placed on the market. At the time, H3N8 was considered a "novel" pathogen: all dogs were at risk of contracting canine influenza because they'd never been exposed to the virus before. Today most dogs have probably been in contact with the virus; the symptoms of canine influenza mimic those of kennel cough, however, and the owners might not even have been aware their dog had the flu. Only a very small number of dogs will develop severe problems, typically as a secondary pneumonia. Dogs at risk include those housed in communal facilities—the disease was first seen at greyhound racing tracks—and those in areas where the virus is known to be causing infections.