half dose vaccine

This new ground-breaking study on half dose vaccine protocols reveals small dogs should not receive the same size vaccine as large breed dogs.

Editor-in-chief note: 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 dose as a 150-pound mastiff. The conventional veterinary community has maintained that this is a safe practice, but over-vaccination can cause a range of health problems and even death. Studies have shown that vaccines last years longer than was initially believed, triggering a new protocol of vaccinating every three years instead of annually (not all veterinarians follow this new protocol). But even every three years is unnecessary, according to research done by the American Animal Hospital Association (AAHA).

If frequency is an issue, then what about dosage? Wouldn’t it be prudent to give as little vaccine as possible in order to mitigate vaccine-related injury? Isn’t that what we do with other medications? Eminent researcher Dr. W. Jean Dodds recently conducted a pilot study to determine if a half dose vaccine would protect small dogs as effectively as the current full-dose now used. For her study, Dr. Dodds chose the canine parvovirus and distemper vaccines. We’re grateful she is sharing this research with us at Animal Wellness.

Efficacy of a half dose canine parvovirus and distemper vaccine in small adult dogs: a pilot study* 


Many veterinary practitioners simply believe what they have been taught about vaccines, and so are less inclined to change or “fix” what is perceived to be unbroken. Other veterinarians use canine vaccination programs as “practice management tools” – annual vaccination has been and remains the single most important reason why most people bring their dogs and cats for an annual or, more often, a “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 the vaccines and vaccination programs based on scientific information have created significant controversy. A “more is better” philosophy still prevails with regard to pet vaccines, but clearly, the accumulated evidence indicates that vaccination protocols should no longer be considered a “one size fits all” program.

With the advancement in vaccinology comes the increased risk of adverse reactions, called vaccinoses, some of which 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!”

vaccine study

Benefits of a half dose vaccine 

One of the concerns about the potential for over-vaccination and its inherent increased risk of adverse vaccine reactions is the question of giving vaccines on a “one-size-fits-all” basis rather than based upon body weight of the dog. Why do toy breed and giant breed dogs receive the same one ml dose of vaccines, when the manufacturer’s vaccine clinical trials are typically performed on laboratory beagles with little field testing in different breed types prior to licensure and clinical use? 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.”

Clinical experience

Five decades of clinical research experience with vaccinations of companion animals by this author and others have shown that the dose of canine distemper virus (CDV) and canine parvovirus (CPV) vaccines can be reduced to 50% for small breed type dogs and still convey full duration of immunity. This experience applied to puppies and older dogs of small breed types that weighed 12 pounds or less as adults. Follow-up serum vaccine titers performed three or more weeks after vaccination documented that more than 95% of these dogs given a half dose of two-way bivalent CDV/CPV (DPV) vaccine mounted what is known to be protective antibody titers to both viruses. To document this clinical field experience, I completed a formal clinical trial study.

Pilot study design and results

Small breed dogs between three and nine years of age participated in a clinical research study to determine whether giving them just a half-dose of a two-way, bivalent DPV vaccine generated a protective serum antibody titer response one month and six months later in comparison to pre-vaccination titer levels. None of these dogs had received a vaccination for at least three years and all were healthy. Informed consent of the owners was obtained.

The result: the half dose 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 post-vaccination.


Results of this study confirmed that small adult dogs that received a half dose of a two-way, bivalent DPV vaccine provided a sustained protective serum antibody response.


*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.