- Almost all states in the U.S. require certain core vaccines for companion animals including dogs, cats and ferrets, with many expected to be repeated annually.
- Vaccine dosages are given on a one-size-fits-all basis, so that Chihuahua puppies and full grown Mastiffs receive the same amount of vaccine.
- Despite data showing that small breeds are more likely to experience adverse reaction to vaccines, research is sparse and one-size-fits-all pet vaccination laws have not changed.
As is the case with vaccination mandates in humans, laws vary by state regarding vaccines required for pets. A few states do not require any vaccines at all, but most states highly recommend several annual vaccines, and all but eight states have laws requiring repeated rabies vaccination for dogs, cats and usually ferrets.1 Rabies vaccination is most commonly required within the first few months of the animal’s life and then either annually or every three years thereafter (fun fact: the one-year and three-year vaccination products are identical except for labeling2).
Citing studies from the top animal vaccine manufacturers in the United States, veterinary immunologist Dr. Ronald Schultz reported that all studies found that core canine vaccines (canine distemper virus, canine parvovirus type 2 and canine adenovirus) sustained their duration of vaccine acquired immunity (DOI) for at least three years and that feline core vaccines (feline parvovirus, calicivirus and herpes virus type I)3 had a DOI of more than three years and did not need to be repeated annually. Many other studies concur that vaccine-induced antibodies are sustained far beyond one year and that annual re-vaccination is unnecessary.4
Vaccines Disregard Size Differences
When human children are vaccinated, they receive the same vaccine dosage regardless of the child’s size, so both the 20-lb one-year-old and the 50-lb six-year-old would receive the same 0.5 mL dose of the MMR (measles, mumps, rubella) vaccine. Even more dramatically, the same rule holds true for the 5-oz Chihuahua puppy and the 200-pound adult Mastiff, or the tiny kitten and the adult lion: same dosage of vaccine, with many of them repeated annually.
The supposed rationale for indiscriminate use of vaccines is the same regardless of species: Vaccines are considered safe, even for preterm or very low weight babies5 (or puppies or kittens) and most vaccine testing is done simply to determine the “lowest effective dose for the target age group.” The explanation offered is that vaccines do not work like drugs, which have a greater effect when concentrated in a smaller body and, therefore, dosage must be adjusted for body weight. Instead, the reasoning goes, vaccines act more like an “on/off switch” to educate injection site immune cells that then circulate throughout the body.6
However, it has also been reported that, “Vaccine developers must practice good medicine and good economics. Giving larger doses of active ingredients than required would increase the side effects from and the costs of vaccines.”7
Isn’t a one-size-fits-all dosage the equivalent of giving a “larger dose of active ingredients” when injected into a baby’s tiny body?
Pet Size Matters in Vaccine Safety
Numerous studies have shown that adverse reactions to vaccines are not uncommon among dogs and range from milder effects such as fever, stiffness, sore joints, abdominal tenderness and behavioral changes to increasingly serious conditions including auto-immune disorders and rabies vaccine-induced development of anti-thyroglobulin autoantibodies implicated in the onset of hypothyroidism. Vaccines have also been linked with an increased susceptibility to infections, cancer, neurologic disorders and encephalitis, as well as with jaundice, organ failure and collapse with auto-agglutinated red blood cells.8
It has also been shown that adverse effects are far more prevalent in small dogs than in larger breeds. In a search of electronic records from 1,226,159 dogs vaccinated at 360 veterinary hospitals, it was determined that not only was the risk for vaccine associated adverse events (VAAE) inversely proportionate to size of the dog, but risk also was “27% to 38% greater for neutered versus sexually intact dogs and 35% to 64% greater for dogs approximately 1 to 3 years old versus 2 to 9 months old.”
The researchers also found that adverse events “significantly increased as the number of vaccine doses administered per office visit increased; each additional vaccine significantly increased risk of an adverse event by 27% in dogs ≤ 10 kg (22 lb) and 12% in dogs > 10 kg.”
It is important to note that in that study, the researchers focused on a very few specific adverse events. They did not report reactions that occurred more than 72 hours after vaccination (so left out reactions such as injection site sarcomas and autoimmune diseases that developed later) or reactions that had not been selected for evaluation, such as seizures or many other common vaccine reactions. They also omitted reactions not reported on time by pet owners and reactions not recognized at the time by veterinarians.9
The authors concluded that, “Young adult small-breed neutered dogs that received multiple vaccines per office visit were at greatest risk of a VAAE within 72 hours after vaccination.10
Dr. Jean Dodds, a well-respected authority on pet vaccines, identified several other factors that may increase the risk for vaccine reactions. Specific breeds, for example, appear to be at increased risk and include Akita, American Cocker Spaniel, Dachshund, German Shepherd, Golden Retriever, Great Dane, Irish Setter, Kerry Blue Terrier, Old English Sheepdog, poodle (all types but especially the Standard Poodle), Rottweiler, Scottish Terrier, Shetland Sheepdog, Shih Tzu, Vizsla and Weimaraner.11 Other conditions that increase risk include all- or predominantly white fur and animals with “diluted” coloring, as in blue and fawn Doberman Pinscherss or Harlequin Great Danes.
More Vaccine Research Needed
Vaccine research generally requires only that a vaccine can be shown to elicit an effect in the breed for which it is intended, so the relatively few animals involved in preclinical testing tend to be of “average” size.12 Recognizing that small breeds would be underrepresented in such studies, Dr. Dodds conducted a small pilot study to evaluate the immunologic effectiveness of giving a half dose of distemper and parvovirus vaccines to dogs weighing less than 12 pounds.
The study set out to document what had been apparent over more than 50 years of clinical and research experience, namely, that a half dose of certain vaccines does provide adequate titer levels (a titer test is a measures the blood for the presence of specific antibodies, whether to vaccine or natural exposure to an infectious agents).13
The 13 small dogs in the study were all between three and nine years of age, had not been given any routine vaccinations for at least three years, and weighed less than 12 pounds. Four-week and six-month titer testing showed sustained antibody levels to both the canine distemper and parvovirus diseases, compared to the pre-vaccination levels. The researchers concluded that the half doses were effective in the small study group, and that the concept merited further study in a larger population.
Three years later, although many references cite this small pilot study, no follow up has been done and one-size-fits-all pet vaccination laws have not been changed to reflect the greater risk of vaccine adverse reactions in small breed pets.
1 State Rabies Vaccination Laws for Domestic Dogs, Cats, and Ferrets in the United States. The Policy Surveillance Program Mar. 9, 2019.
2 Campbell Thornton K. AVMA 2017: Rabies Vaccination – What You Need to Know. American Veterinarian July 25, 2017.
3 Schultz RD. Duration Of Immunity For Canine And Feline Vaccines: A Review. Science Direct Oct. 2006.
4 Brady C. So Humans Need to be Vaccinated for Viruses as Babies and That Lasts for Life but Dog Vaccinations Need to be Given Every Year?! DogsFirst.ie.
5 Immunizations For Preterm Babies. HealthyChildren.org Aug. 23, 2017.
6 What’s the Right “Dose” of a Vaccine for Small-Breed Dogs? SkeptVet.com Jan. 18, 2016.
7 Vaccine Schedule: Other Schedule Issues. Children’s Hospital of Philadelphia Mar. 18, 2019.
8 Brady C. Dog Vaccinations Part 2: Side Effects. DogsFirst.ie.
9 Rasmusen J. Vaccinating Small Dogs: Risks Vets Aren’t Revealing. Truth4Dogs.com Sept. 30, 2009.
10 Moore GE, et al. Adverse Events Diagnosed Within Three Days Of Vaccine Administration In Dogs. J Amer Vet Med Assoc Oct. 1, 2005.
11 See Footnote 8.
12 Khuly K. Smaller Dog, Smaller Vaccine. The Daily Vet July 27, 2011.
13 Dodds WJ. A Pilot Study: 1/2 Dose Vaccines for Small Dogs. Hemopet Jan. 17, 2016.