Adverse vaccine reactions in pets

Adverse reactions usually occur because of a harmful immune-mediated reaction to either the vaccine immunogen itself or to the vaccine adjuvants, which are designed to boost the immune response to the vaccines. The immunogens may consist of killed or inactivated pathogens, bio-engineered pathogen proteins or polypeptides, or, increasingly rarely, modified live virus.

There have been no specific associations between development of vaccine-associated sarcoma and vaccine brand or manufacturer, concurrent infections, history of trauma, or environment.[5]

In 1993, a causal relationship between VAS and administration of aluminum adjuvanted rabies and FeLV vaccines was established through epidemiologic methods.[6]

In addition to vaccine-specific factors, vets and owners should also consider pet-specific factors that have been shown to increase the risk of adverse reactions in both dogs[1] and cats.[2] Examples of such factors include:

• age,
• number of vaccinations per office visit,
• size,
• general health of the animal,
• breed,
• neutered status, and
• past vaccination history.

A little known and often misdiagnosed reaction to the rabies vaccine in dogs, this problem may develop near or over the vaccine administration site and around the vaccine material that was injected, or as a more widespread reaction. Symptoms include ulcers, scabs, darkening of the skin, lumps at the vaccine site, and scarring with loss of hair. In addition to the vaccination site, lesions most often develop on the ear flaps (pinnae), on the elbows and hocks, in the center of the footpads and on the face. Scarring may be permanent. Dogs do not usually seem ill, but may develop fever. Symptoms may show up within weeks of vaccination, or may take months to develop noticeably.

Dogs with active lesion development and / or widespread disease may be treated with pentoxyfylline, a drug that is useful in small vessel vasculitis, or tacrolimus, an ointment that will help suppress the inflammation in the affected areas.

Owners and veterinarians of dogs who have developed this type of reaction should review the vaccination protocol critically and try to reduce future vaccinations to the extent medically and legally possible. At the very least, vaccines from the same manufacturer should be avoided. It is also recommended that the location in which future vaccinations are administered should be changed to the rear leg, as far down on the leg as possible and should be given in the muscle rather than under the skin.

Fortunately, severe systemic reaction to vaccine allergy is very rare in dogs. When it does occur, however, anaphylaxis is a life-threatening emergency. More often, dogs will develop urticaria, or hives within minutes of receiving a vaccine. When this occurs, a veterinarian will treat the reaction with antihistamines and corticosteroid drugs and this is usually effective. Future vaccine protocols must be modified according to the vaccine component suspected to have triggered the reaction.

FVRCP vaccines have also come under scrutiny of late due to possible risks to long term health. A study at Colorado State University noted an association between vaccination with parenteral (injectable) FVRCP vaccinations and development of antibodies against feline kidney tissue.[7] Antibody development is hypothesized to develop when the immune system reacts to protein contaminants from the cell line used to cultivate vaccinial viruses. The cell line in question, the Crandell-Rees Feline Kidney (CRFK) cell line, was derived from a cat kidney. It is currently unknown whether this antibody development can lead to renal disease, though a recent follow-up study demonstrated evidence of inflammation on re-biopsy samples from some of the study cats.[8]

A Vaccine-associated sarcoma (VAS) is a type of malignant tumor found in cats (and rarely, dogs and ferrets) that has been linked to certain vaccines. Concern about VAS has resulted in changes in recommended vaccine protocols to limit the type, frequency, and sites of vaccinations. Owners are advised to monitor injection sites for signs of tumors and contact their veterinarian immediately if one develops.

Vaccines should be given in specific areas in order to: ease identification of which vaccine caused an adverse reaction, and ease removal of any vaccine-associated sarcoma.[12]

In North America, vets adopted the practice of injecting specific limbs as far from the body as possible,[13] with the rear right for rabies, the rear left for leukemia, and the right front shoulder (being careful to avoid the midline or interscapular space) for other vaccines (such as FVRCP).

This set of locations was not widely adopted outside of North America, and the international Vaccination Guidelines Group (VGG) made new recommendations[3] that vaccines be administered:

• in subcutaneous (and not intramuscular) sites
• in the skin of the lateral thorax or abdomen (for easier excision of any FISS that occur)
• avoid the interscapular or intercostal regions (as more extensive surgical resection would be needed for sarcomas)
• in a different site on each occasion (either with general locations per species per year or diagrams of where administered on specific visit)

In the 2010 recommendations of the international Vaccination Guidelines Group (VGG),[3] they emphasized the importance of administering non-adjuvanted vaccines whenever possible.

The VGG also prefers serological testing over unnecessary re-vaccination or boosters of core vaccines after the initial 12-month booster that follows the puppy/kitten series of modified live virus [MLV] vaccines. This is because core vaccines show an excellent correlation between the presence of antibody and protective immunity and have a long DOI (Duration of Immunity). Antibody tests can be used to demonstrate the DOI after vaccination with core vaccines, though not for non-core vaccines.