A Pilot Study: 1/2 Dose Vaccines for Small Dogs

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A Pilot Study: 1/2 Dose Vaccines for Small Dogs | Jean Dodds, DVM


For the past two years, I have conducted a pilot study on whether or not a half-dose distemper and parvovirus vaccine elicited enough immunity to these viruses in adult dogs weighing less than 12 pounds. I thank the American Holistic Veterinary Medical Foundation for supporting this study and am pleased to share the results with you. The full study results are published in the Journal of American Holistic Veterinary Medical Association and Animal Wellness. Additionally, please feel free to peruse the references at the bottom of this article. 

The Basic Foundation: What you need to know

What is Parvovirus?
The canine parvovirus (CPV) infection is a highly contagious, ubiquitous viral illness that affects dogs, and the parallel ubiquitous feline parvovirus (named feline panleukopenia virus, FPV) affects cats. These viruses manifest in different forms. The more common form is the intestinal form, which is characterized by vomiting, diarrhea, weight loss, and lack of appetite (anorexia). The less common form is the cardiac form, which attacks the heart muscles of very young puppies, often leading to death. The majority of cases are seen in puppies that are between six weeks and six months old. – PetMd.com

In kittens infected in utero from their asymptomatic or mildly ill dams, cerebellar hypoplasia, stillbirths and neonatal death occur. For those that survive, the small cerebellum leaves them ataxic and uncoordinated. 

What is Distemper?
Canine distemper (CDV) is a contagious and serious viral illness, usually with no known true cure. The virus, which is spread through the air and by direct or indirect (i.e. utensils, bedding) contact with an infected animal, initially attacks a dog’s tonsils and lymph nodes and replicates itself there for about one week. It then attacks the respiratory, urogenital, gastrointestinal, and nervous systems. In the initial stages of distemper, the major symptoms include high fever, reddened eyes, and a watery discharge from the nose and eyes. An infected dog will become lethargic and tired, and will usually become anorexic.

Persistent coughing, vomiting, and diarrhea may also occur. In the later stages of the disease, the virus starts attacking the other systems of the dog’s body, particularly the nervous system. The brain and spinal cord are affected and the dog may start having fits, seizures, paralysis, and attacks of hysteria. – PetMd.com

What is a titer test?
A titer test is a simple blood serum test that measures the presence of antibodies to vaccine or naturally exposed viruses or other infectious agents.

Immunizing against parvovirus and distemper.
According to the American Animal Hospital Association’s (AAHA) 2011 vaccination guidelines, distemper and parvovirus vaccines are part of the necessary “core” vaccines that every dog should have along with adenovirus-2 (protects against infectious canine hepatitis and part of the kennel cough complex) and rabies.

In the United States, rabies is governed by state and municipal laws. I will be disregarding the rabies topic in this article as clinical trials to change rabies laws are currently underway and rabies titers are performed at Kansas State University. I do not condone or recommend giving half-doses of the rabies vaccine as the law currently states the whole vial must be administered – regardless of size of dog – for  the dog to be considered vaccinated. The same applies to cats where rabies vaccine is mandated.

Regarding distemper, adenovirus-2, and parvovirus vaccines, AAHA recommends vaccinating puppies every three to four weeks between the ages of 6 and 16 weeks. The final dose should be administered at 14 to 16 weeks of age to reduce maternal antibody interference. Additionally, the association suggests vaccinating again at one year of age against these diseases, then every three years moving forward.

I applaud the AAHA guidelines committee for changing its recommendation of annual distemper, parvovirus and adenovirus vaccinations to every three years. This is a big leap forward! However, I respectfully disagree with part of this protocol:

  • Most importantly, it has been found through titer testing that the initial puppy vaccinations generally provide lifelong (NOT lifetime) immunity in the majority of dogs. By the time a dog may have reduced antibody levels that warrant revaccination, he is generally 10 years of age or older and the vaccination can be more risky and elicit adverse events at that age. The senior dog is also more than likely not in situations that would necessitate it.
  • I do not recommend the adenovirus-2 vaccine for hepatitis because until just recently in some dogs from one litter, there have been no documented clinical cases of infectious canine hepatitis in North America for at least 15 years. If an outbreak occurs regionally, then I will likely change my mind based on the situation and only for the affected region. Further, a published study showed that combining adenovirus with CDV in modified live vaccines (MLV) vaccines causes cell-mediated immune suppression for up to 10 days afterwards at an age when young pups are going through the changes of new homes, diets, and environment.
  • I generally do not recommend vaccinating puppies against these clinically important infectious diseases before the age of 9 weeks due to the partial neutralizing effect of residual maternal antibodies that are provided in the colostrum of mother’s milk. The exception would be an endemic local parvovirus outbreak where giving a single monovalent CPV vaccine may be needed as early as 5-6 weeks of age.
  • If the first distemper and parvovirus vaccine is properly timed between the 9-10 weeks of age mark, the same given at the age of 14-15 weeks, and a parvovirus only vaccination at 18 weeks should immunize them effectively.

The type of vaccine administered.
Distemper, parvovirus and adenovirus are MLV. As the name suggests, MLV vaccines use a modified, but weakened, form of the live microorganism(s). When the virus is injected into the body, it multiplies many-fold and stimulates the immune system’s production of antibodies, creating an immune response that protects the body against future exposure to the disease. For these 3 viruses and FPV of cats, true immunization prevents further infection, a process known as “sterile immunity”.

MLV vaccines have been associated with the development of temporary seizures in both puppies and adult dogs of breeds or crossbreeds susceptible to immune-mediated diseases. When MLV vaccines are given to pets with compromised immune systems, the animal is actually at some risk of contracting a weakened form of the virus from the vaccine.

The Small Breed Half-Dose Vaccine Pilot Study Results

What is a pilot study?
A pilot study, pilot project or pilot experiment is a small scale initial study conducted in order to evaluate feasibility, time, cost, adverse events, and effect size (statistical variability) to predict an appropriate sample size and, if needed, improve upon the study design prior to performance of a full-scale research project. – adapted from Wikipedia

Even with the convincing results of the pilot study, changes in current vaccine guidelines will likely take years to implement.

For decades, the human and animal immunological communities have asserted that vaccines are “one size fits all”. 

The premise is that even though patients are not the same, the immune system response is similar. While exceptions do exist in human vaccines, dosages basically come in two amounts: adult and pediatric. I have questioned the “one size fits all” claim for years. 

The human population, of course, has much less variability in size compared to dogs. For instance, an 8 week old St. Bernard puppy will weigh approximately 8 pounds and will grow to approximately 160 pounds. An 8 week old Papillon will weigh approximately 2 pounds and will be approximately 9 pounds as an adult. Common sense begets that the Papillon does not need the same vaccine dosage amount as a St. Bernard. Indeed, medications, heartworm preventatives, food, collars, harnesses and even dog clothing are based on size. Could you imagine feeding a Papillon two pounds of food a day? It would be unfathomable!

Case in point, vaccine products are stated to provide a sufficient excess of antigen for the average-sized animal so they are likely to be either too much for the toy breeds or too little for the giant breeds. Although the minimum immunizing doses have been established, the optimum dosages required for disease protection have yet to be determined.

What we do know based upon nearly 5 decades of clinical and research experience with vaccinations in companion animals: the dose of CDV and CPV vaccines can be reduced to 50%, but not more, for small breed and small mixed breed type dogs, based upon their body weight, and still convey full duration of immunity. This applies to puppies and older dogs of small breeds and breed types that weigh 12 pounds or less as adults. Serum vaccine antibody titers have also been performed 3 or more weeks after vaccination. As reported for dogs given a full dose of vaccine, greater than 95% of the dogs given a full or a half dose mounted what is considered to be protective antibody titers to both canine distemper and parvovirus.

Study Objective
The purpose of the recently completed study was to document the serum antibody titer responses from administering a half-dose of a bivalent distemper/parvovirus vaccine to small breed adult dogs that had not been vaccinated in at least 3 years.

Sample Size and Population Characteristics
13 small breed dogs

Sample Population Characteristics
–  Between the ages of 3 and 9
–  Weighed 12 pounds or less
–  No routine booster vaccines for at least 3 years 

Method and Timeline
1.  Whole blood sample collected that was sent to Hemopet’s Hemolife Diagnostic Laboratory for baseline antibody level testing (titer).
2.  Veterinarian administered half-dose distemper/parvovirus vaccine.
3.  4 weeks post-vaccination: blood sample drawn and sent to Hemolife for titer testing.
4.  6 months post-vaccination: blood sample drawn and sent to Hemolife for titer testing. 

The 4-week and 6-month titer tests demonstrated that antibody levels to the canine distemper and parvovirus diseases had a sustained increase in all of the study’s dogs compared to the pre-vaccination blood sample. As the presence of measurable canine distemper and parvovirus serum antibody titers reflect immunity to these viruses, and given that vaccines are known to cause adverse events, especially in smaller dogs, results of this study confirmed that receiving a half-dose of canine distemper/parvovirus vaccine was efficacious for this study cohort. Further investigations could address a larger number of smaller canines.

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843

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