Ron Schultz, Ph.D., Professor and Chair of the Department of Pathobiological Sciences at the University of Wisconsin School of Veterinary Medicine, and Tom R. Phillips, D.V.M., Ph.D., wrote in Kirk's Current Veterinary Therapy XI (a book even conventional veterinarians most likely have on the shelf) that:
"A practice that was started many years ago and that lacks scientific validity or verification is annual revaccinations. Almost without exception there is no immunologic requirement for annual revaccination. Immunity to viruses persists for years or for the life of the animal. Successful vaccination to most bacterial pathogens produces an immunologic memory that remains for years allowing an animal to develop a protective anamnestic (secondary) response when exposed to virulent organisms.
Only the immune response to toxins requires boosters (e.g., tetanus toxin booster, in humans, is recommended once every seven to ten years), and no toxin vaccines are currently used for dogs or cats.
Furthermore, revaccination with most viral vaccines fails to stimulate an anamnestic (secondary) response as a result of interference by existing antibody (similar to maternal antibody interference).
The practice of annual vaccination in our opinion should be considered of questionable efficacy unless it is used as a mechanism to provide an annual physical examination or is required by law."
In Plain English: This means that the authors believe there is no valid scientific reason to vaccinate pets every year.
That practice, instead, emerged as a default judgement between the pharmaceutical companies making the vaccines, and the veterinarians.
The vets wanted to get their patients in once a year for a check-up, and the vaccine makers wanted to sell more vaccines.
Tying the annual physical to vaccines was a stroke of genius.
It simplified life for veterinarians, who now only had to say "We'll see Fluffy next year for his shots" and send a postcard, and it made boatloads of money for the drug companies.
When this "suggestion" was added to vaccine labels, it added an air of "requirement" and ensured that the system would continue to make everyone happy. At the time, vaccines were considered benign and harmless -- so this lucrative state of affairs went unquestioned until the late 1980s, when vaccines began to be linked to injection-site cancers in cats.
Today, it is known that vaccines are not so harmless, and they are now considered a medical procedure like any other, with both risks and benefits.
In order to realistically assess the situation and make wise decisions for our dogs and cats, we need to examine the big question on animal companions minds today.
If your dog had its puppy shots and a subsequent "Booster" shot a year later, its probably covered for life.
You CAN TEST for this. Its called a Titre Test. You can ask your vet to do it for you.