Should small dogs receive a half dose vaccine?


A new ground-breaking study reveals that small dogs should be receiving a half dose vaccine, rather than the same size vaccine as large breed dogs.

You may have noticed during the last few visits to your veterinarian that recommended vaccine protocols have changed significantly. Dogs used to be vaccinated every year, but research conducted by a vaccine task force of the American Animal Hospital Association (AAHA) showed that some core vaccines actually provide protection for up to seven years (and possibly longer) after the first year boosters.

sidebar core vaccinesThe results of this task force helped change core vaccine frequency from annually to every three years. It also increased the awareness and popularity of vaccine titers – blood tests that veterinarians use to measure an individual dog’s current immunity status to various diseases.

Since we know over-vaccination can cause a range of health problems and even death, it makes sense to vaccinate only when a dog requires protection. Core vaccines are not mandatory, after all, with the exception of Rabies, so shouldn’t they be updated when required, as with human vaccines?

A close look at vaccine dosages

If frequency is an issue, then what about dosage? Currently, all dogs, no matter what the size or breed, are vaccinated with the same quantity of vaccine. A five-pound Chihuahua receives the same 1 ml dose as a 150-pound mastiff. Eminent researcher and veterinarian Dr. W. Jean Dodds, says small dogs may be getting “too much of a good thing”. Dr. Dodds recently conducted a pilot study on Canine Parvovirus and Distemper Vaccine (DPV) to determine if a half-dose would protect small dogs as effectively as the current full-dose.

Canadian Dogs Annual talked to Dr. Dodds about this issue and her findings:

CDA: Pet vaccination seems to be a controversial issue, with some veterinarians adopting the new three-year protocol but others still vaccinating every year. Why is that?

Dr. D: Many veterinary practitioners simply believe what they originally learned about vaccines, and so are less inclined to change or “fix” what is perceived to be unbroken. Other veterinarians seem to use canine vaccination programs as a means to draw clients into the office. Annual vaccination has been the single most important reason why the majority of people bring their dogs and cats for an annual check-up or “wellness visit”. When you combine this with a failure to understand the principles of vaccinal immunity (that portion of immunity conveyed by vaccines), it is not surprising that attempts to change vaccines and vaccination programs have created significant controversy.

small dog and big dogCDA: Why is over-vaccination a concern?

Dr. D: With the advancement in vaccinology comes the increased risk of adverse reactions, called vaccinoses. Some of these are serious, chronically debilitating and even fatal. We need to balance the need to protect animals against serious infectious diseases with the attendant risk of adverse events.  As vaccine expert Dr. Ron Schultz states, “Be wise and immunize, but immunize wisely!”

CDA: Why did you tackle this particular study to determine if smaller dose vaccines would provide adequate protection for small dogs?

Dr. D: One of the concerns about the potential for over-vaccination is the question of giving vaccines with a “one size fits all” approach rather than basing them on the body weight of the dog. Why do toy and giant breed dogs receive the same 1 ml dose of vaccines, when the manufacturer’s vaccine clinical trials are typically performed on laboratory beagles and with little field testing in different breed types?

“Vaccines should be thought of as medications – use as little as possible to accomplish what’s needed.”

Surely, a giant breed dog should require more vaccine than a small or medium-sized dog to fully immunize, and toy and smaller breeds logically would need even less. As Dr. Link Wellborn, Chair of the 2011 AAHA Canine Vaccine Task Force, stated in the article “Injecting insight into vaccinations”, Vaccines should be thought of as medications – use as little as possible to accomplish what’s needed.”

CDA: Who participated in the study?

needleDr. D: We worked with small breed dogs that weighed 12 pounds or less, who were between three and nine years of age. None of these dogs had received a vaccination for at least three years and all were healthy.

CDA: What were the results of the study?

Dr. D: The half-dose DPV vaccine generated increased serum vaccine antibody titers for all the dogs studied. The median titer and endpoint titer levels had a sustained increase in all dogs at six months after vaccination. So the half-dose did provide a sustained protective serum antibody response.

CDA: Any final thoughts?

Dr. D: A “more is better” philosophy still prevails with regard to pet vaccines, but clearly, the evidence indicates that vaccination protocols should no longer be considered a “one size fits all” program.


*Dodds, WJ.Efficacy of a half-dose canine parvovirus and distemper vaccine in small adult dogs: a pilot study”.  JAHVMA 41:12-21, Winter, 2015.

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Dana Cox is the co-founder, Chief Creative Officer and editor-in-chief of Redstone Media Group, which publishes Canadian Dogs Annual, Animal Wellness Magazine, Equine Wellness Magazine and Integrative Veterinary Care Journal, and associated websites. She regularly attends veterinary conferences to stay apprised of leading edge and best practice therapies and modalities. Dana lives in Peterborough, ON with her husband and fellow co-founder, Tim Hockley, and their family which includes two children, a dog and a cat.