Although not as common as with people, adverse reactions to vaccines, or undesired side effects, also can occur in pets. However, compared to the risks of not vaccinating dogs and cats, the risks associated with vaccinations are very minimal. Adverse effects from vaccinations can vary with the type of vaccine used, and the age and breed of animal vaccinated.

The most common adverse reaction to vaccinations are mild and short lived. Your pet may develop slight redness, swelling or tenderness at the injection site. You may notice a decreased appetite, slight fever and increased tiredness for 1 -2 days following vaccination. These symptoms are generally mild and require no treatment other than some extra tender loving care and attention.

Occasionally, a dog will experience discomfort and swelling at the injection site which develops into a sterile abscess. These abscesses are generally not caused by infection, but by the body's over-reaction to the vaccine. If the swelling or inflammation do not clear up in 1 -2 days, call your veterinarian for a follow up visit.

Some studies have shown that dogs with atopy who are vaccinated at the height of the allergic season may have an increased risk of developing more severe allergies. It is suggested that dogs with seasonal allergies be vaccinated during the 'non-allergy' season.

There are some unusual but serious adverse reactions that all pet owner's need to be aware of.

Anaphylaxis
Anaphylaxis is an uncommon, life-threatening, immediate allergic reaction to something ingested or injected. It can result in shock, respiratory and cardiac failure, and in extreme cases, death. If a vaccination is the cause of an anaphylactic reaction, the onset will be rapid, usually within minutes.

The symptoms to watch for are:
• sudden onset of diarrhea or vomiting
• swelling of the face
• rapid heartbeat with weak pulse
• pale gums
• cold limbs
• shock, seizures, coma, and death.

Anaphylactic reactions can occur with the use of killed vaccines such as Rabies, Canine Coronavirus, and Leptospirosis. Killed vaccines have more viral or bacterial particles per dose and have added chemicals to improve the animal's immune response. These characteristics also increase the risk of an allergic reaction to the vaccine.

Before you attempt an in-house vaccination program, have your veterinarian instruct you in the emergency procedures for this reaction. You should have epinephrine available and know how to use it in an emergency. It could mean the difference between life and death for the animal.

Neurological problems and eye disease
Another possible serious complication from vaccination is the appearance of neurological symptoms. Canine distemper vaccination is the most common cause of neurological disease, and can cause an inflammation of the brain. Cerebellar disease has been reported in puppies and kittens less than 5 weeks of age who were vaccinated with a modified live vaccine.

Intranasal Vaccine Risks
Severe illness can occur if vaccines designed for intranasal use are accidentally injected. If an internasal vaccine is spilled, immediately clean it up and wipe down the area with a bleach solution. Illness can also occur if your pup licks any spilled vaccine off his or her skin, so clean the dog as well. Severe reactions can also occur if any of a vaccine made for injection accidentally enters an animal's eyes, nose, or mouth. It is important to watch for the onset of a mild cough that seems to be unrelated to any other symptoms. Although additional treatment is usually not needed, the infected dog may pass the illness to other animals via the cough.

Birth defects or infections
To prevent serious birth defects, always be certain that female animals are not pregnant when vaccinated. The vaccination of pregnant animals with a modified live vaccine can result in birth defects or abortions. It is recommended that modified live vaccines never be given to pregnant animals.

Additionally, very young animals are at risk with live vaccines. Vaccinating puppies and kittens less than 4-5 weeks of age, is usually not necessary. At this young age, the puppies will still be protected by the maternal antibodies passed on by their mother.