The latest on vaccinations

We’ve known about the risks of over-vaccination for awhile now, though many veterinarians, trainers, boarding kennel operators and others still promote yearly boosters. Learn which vaccines are really necessary, and when, and how to protect your companion from their side effects.

By now, many savvy animal lovers are aware of the dangers of over-vaccination, and are opting against annual boosters for their dogs and cats. While there’s no doubt that vaccines effectively protect companion animals against serious infectious disease, there’s also no doubt that over-vaccination can cause serious disease of a different kind.

For more than a decade now, scientifically based information has lead to revised guidelines and policies about companion animal vaccines. So why are so many veterinarians, as well as training, boarding and grooming facilities, still reluctant to embrace and apply this knowledge?

Why the resistance to change?

Veterinary practitioners may simply believe what they were taught about vaccines, so don’t take the time or have the inclination to change or “fix” what is perceived to be unbroken. As well, vaccination programs have been promoted as “practice management tools” rather than medical procedures. A “more is better” philosophy still prevails with regard to dog and cat vaccines.

Annual vaccination has long been the single most important reason why most people take their animals to the vet for an annual “wellness visit”. Another reason for the reluctance to change current vaccination programs is that many practitioners really don’t understand the principles of vaccinal immunity (that portion of immunity conveyed by vaccines). The accumulated evidence indicates that vaccination protocols should no longer be considered as a “one size fits all” program.

This article outlines approaches that balance the need to protect animals against serious infectious diseases with the risk of adverse events from vaccines. As my colleague, Dr. Ron Schultz of the University of Wisconsin, states: “Be wise and immunize, but immunize wisely!”

Adverse reactions to vaccination

Vaccine reactions usually occur in puppies, kittens or older animals that are genetically predisposed to react adversely when vaccinated.

• The associated clinical signs typically include fever, stiffness, sore joints and abdominal tenderness, susceptibility to infections, neurological disorders and encephalitis, autoimmune thyroid disease, severe anemia and jaundice from destruction of red blood cells, and pinpoint or larger hemorrhages from platelet destruction.

• Liver enzymes may be markedly elevated, and liver or kidney failure may occur by itself or accompany bone marrow suppression.

• Both modified-live virus (MLV) and killed inactivated vaccines, such as those for canine distemper and rabies, respectively, have been associated with post-vaccinal encephalitis (PVE). This can result in various clinical and behavioral signs.

• An augmented immune response to vaccines is seen in dogs with pre-existing inhalant allergies (atopy) to pollens, grasses, weeds and trees.

• In cats and dogs, aggressive tumors (fibrosarcomas) can occasionally arise at the site of vaccination. Other cancers such as leukemia have also been associated with vaccines.

• Additionally, vaccinating dogs with rabies vaccine, either alone or with other vaccines, can induce production of antithyroglobulin autoantibodies, which can contribute to the subsequent development of hypothyroidism.

Other issues that arise from over-vaccination include the increased cost. Having your animal receive annual boosters when they’re not necessary means you’re paying for a service that is likely of little benefit to his existing level of protection against these infectious diseases. Repeated exposure to the foreign substances in vaccines also increases the risk of adverse reactions.

Focus on core vaccines

The concept of “core” vaccines was developed some years ago to distinguish vaccines that every dog and cat should have, from those that are “non-core” (optional or depend on the region/area where the animal lives).

For dogs, there are four core vaccines:

• Canine distemper virus

• Canine parvovirus

• Canine adenovirus (hepatitis)

• Rabies virus

Note that cross-protection against canine adenovirus-1 (CAV-1, infectious canine hepatitis virus) is provided by canine adenovirus-2 (CAV-2, kennel cough) vaccines; the original CAV-1 vaccines produced an immune precipitate in the eye called “blue eye”. But except for one incident at the Canadian/US east coast border area several years ago, there have been no documented cases of CAV-1 disease in North America for at least 15 years. That’s the reason why veterinarians like myself prefer not to give this vaccine, especially to puppies, as it can cause immune suppression for about ten days when given together in an MLV CDV combo vaccine (you cannot obtain CAV-1 vaccine by itself).

There are also four core vaccines for cats:

• Feline panleukopenia, a parvovirus

• Feline calicivirus

• Feline herpesvirus-1

• Rabies virus

The first vaccination should not be given before six weeks of age and is best given later (e.g. eight to ten weeks), since most puppies and kittens of vaccinated mothers are protected by their residual maternal immunity. Either two or three boosters are given, with the last one at 14 to 16 weeks of age. Rabies vaccine should be given separately whenever possible, and as late as allowed by local, state or provincial law.

These core vaccines are important for protecting dogs and cats against the most serious and prevalent infectious diseases, and all puppies and kittens should receive them. However, even the core vaccines (including rabies – see next page) are being shown to have a much longer duration of immunity than previously thought, making annual boosters unnecessary.

Non-responders and low responders

Animals that don’t develop any or enough protective antibodies when vaccinated for a particular disease are known as non-responders or low responders. This situation is a genetic trait, and the animals will remain susceptible to the disease in questions all their lives. It’s relatively rare, but some breeds are more prone than others:

  • 1:1,000 for CPV (parvovirus) — especially in black Labradors and Akitas
  • 1:5,000 for CDV (distemper virus) — especially in greyhounds
  • Zero for CAV (hepatitis, adenovirus)
  • Rate of occurrence in cats is unknown

Vaccine reactions– some stats for dogs and cats

Check out these findings from a study published in the Journal of the American Veterinary Medical Association in 2005.

Canine vaccine adverse events:

• Retrospective cohort study; 1.25 million dogs vaccinated at 360 veterinary hospitals

• 38 adverse events per 10,000 dogs vaccinated

• Inversely related to dog weight

• Vaccines prescribed on a one-dose-fits-all basis, rather than by body weight

• Increased for dogs up to two years of age, then declined

• Greater for neutered versus sexually intact dogs

• Increased as number of vaccines given together increased

• Increased after the third or fourth vaccination

• Genetic predisposition to adverse events documented

Factors that increase risk of adverse events three days after vaccination:

• Young adult age

• Small breed size

• Neutering

• Multiple vaccines given per visit

Feline vaccine adverse events:

• Retrospective cohort study; 0.5 million cats vaccinated at 329 veterinary hospitals

• 51.6 adverse events per 10,000 cats vaccinated

• Inversely related to cat weight

• Increased for cats about one year of age

• Greater for neutered versus sexually intact cats

• Increased as number of vaccines given together increased

• Lethargy with or without fever was most common sign

Factors that increase risk of adverse events 30 days after vaccination:

• Young adult age

• Neutering

• Multiple vaccines given per visit

7 things you can do

There are several steps you can take to help protect your animal companion from the adverse effects of overvaccination.

  1. Ask to have titer tests done on your dog or cat in lieu of annual or three year boosters.
  2. Concentrate on core vaccines, and avoid additional unnecessary vaccines.
  3. Be cautious about vaccinating sick or febrile individuals.
  4. Work with your vet to tailor a specific minimal vaccination protocol, especially for animals of breeds or families known to be at increased risk for adverse reactions.
  5. With a puppy or kitten, start the vaccination series later, such as nine or ten weeks of age when the immune system is more able to handle antigenic challenge.
  6. Pay particular attention to the puppy or kitten’s behavior and overall health after vaccination.
  7. Avoid re-vaccination of individuals that have already experienced a significant adverse event.

The problems associated with over-vaccination have been getting a lot of attention over the past ten years or so, and even though many veterinarians and other animal professional appear unwilling to accept what recent research has been telling us, the tide is turning.


Dr. Jean Dodds received her veterinary degree in 1964 from the Ontario Veterinary College. In 1986, she established Hemopet, the first non-profit national blood bank program for animals. Today, Hemopet also runs Hemolife, an international veterinary specialty diagnostics service. Dr. Dodds has been a member of many committees on hematology, animal models of human disease and veterinary medicine. She received the Holistic Veterinarian of the Year Award from the AHVMA in 1994, has served two terms on the AHVMA’s Board of Directors, chairs their Communications Committee, and currently serves on the Board of the AHVMF, as well as its Research Grant and Editorial Committees.