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Vaccination Reaction!
by T J Dunn, DVM

Vaccine reactions!  Vaccination induced reactions in dogs and cats appear unexpectedly and create anxious moments for the veterinarian, pet owner and the patient.  This page displays one example of a dog with a vaccine reaction to a Rabies vaccine, manufactured by a reputable and professional veterinary pharmaceutical company and administered subcutaneously as recommended.  Twelve  months prior to the Rabies vaccine given in this example the dog, a three year old Dachshund, was vaccinated with a multivalent vaccine containing Distemper, Hepatitis, Parainfluenza, Corona and Parvo virus antigens.  A mild reaction occurred to that vaccine administration.  It is unknown to which fraction of that vaccine the dog reacted.

Prior to the Rabies vaccination given in the example here, the owners were fully informed about potential vaccine reactions and what to do if another one occurred.  They requested a Rabies vaccine only (they decided against giving further multivalent vaccinations) in order to conform to local ordinances and to ensure against possible infection from Rabies due to the abundant wildlife present in the dog's environment.  The vaccine was administered after a discussion of potential good and undesirable effects of a vaccine.

Two hours after the Rabies vaccine was administered the dog was readmitted for itching and head-shaking, and the presence of "hives" on the dog's face and head.  These eruptions on the skin, called a urticarial reaction, are rounded swollen raised areas of skin tissue that have responded locally to the administration of a substance to which the dog is allergic.  Hives are caused when the body releases histamine from a cell called a Mast Cell. The Histamine then causes leaking of fluid into the surrounding body tissues from the small blood vessels and stimulates the nearby nerve endings producing the itching sensation. The dog was breathing normally but was uncomfortable.  Fortunately the vast majority of vaccine reactions in the dog are similar to this case where the targeted tissue is the skin.  It is very rare, but can happen, that the tracheal, laryngeal and bronchial tissues will swell causing a constricted and spastic airway.  Breathing difficulty results that can be very swift in onset and have life-threatening consequences. 

Click on an image below to see a full sized view

TREATMENT FOR VACCINE REACTIONS:
For non life-threatening reactions such as are confined to the skin, anti-histamines and cortisone are generally completely and rapidly helpful.  In severe cases where immediate relief from life-threatening distress is appropriate, epinephrine may be administered by a veterinarian. 

Shock is also seen with some vaccine induced reactions where the patient's heart rate is slowed, blood pressure drops and the patient weakens and will collapse.  Pale mucus membranes and grayish appearing tongue also are evident.  These cases of vaccine induced shock can be very dangerous and often require immediate medical assistance.  These shock reactions usually occur immediately after a vaccine is administered and the patient becomes distressed while still in the veterinarian's office.  Trained personnel will administer appropriate intravenous fluids and medications to restore vital signs and assist with the patient's recovery.  Shock reactions often are reversed in a brief period of time.  Epinephrine and cortisone generally are administered.

VIEW A VIDEO OF A VACCINE REACTION IN A DOG
The dog in the videos below experienced a mild, generalized reaction to vaccines inoculated 90 minutes prior.  The owners noticed after their visit to the animal hospital that their dog was becoming progressively depressed, began displaying patches of skin that were swelling and reddened, and the he appeared tired and uninterested in his surroundings.  They called the  animal hospital and were told to return immediately to the veterinarian whereupon examination revealed what was consistent with an immune reaction.  The probability was that the reaction was a result of one of the several vaccines administered earlier that day.  Keep in mind, too, that spider bites, bee stings, food antigen allergy and inhalant substance sensitivity could also have been the true cause of this dog's reaction.  On several occasions I have observed patients that were admitted shortly after an observed bee sting where the patient has acted exactly as the two cases presented on this page.  Although there are several possible causes of or sources for this reaction, and it may not have been to any vaccine antigen, careful consideration is now given to these patients regarding the pros and cons for any follow-up vaccinations.

REVACCINATION:
Revaccination with the same substances after any post-vaccine episode may result in one of the following three situations:
1.)  No evidence of any inappropriate reaction or adverse effects and the animal will increase its immunity to the disease(s)  for which it is being protected.
2.)  A similar vaccine induced reaction will occur, just like the original reaction.
3.)  A more severe and potentially fatal vaccine induce reaction will occur.

As you can see it is extremely important to consider the RISKS VERSUS BENEFITS topic with your veterinarian whenever a vaccine is administered.  When a reaction does occur, to revaccinate for the same diseases anytime later in the patient's life may be hazardous.  Where legally mandated vaccines are required, and your pet has had a reaction to the required vaccine, your veterinarian should be your advocate and write a statement on animal hospital letterhead that the patient should be exempt from subsequent vaccinations for the disease because of the potential for another vaccine induced reaction.