It is important to understand that vaccine reactions are due to an individual's sensitivity to the vaccine, not because the vaccination is bad or administered improperly. As an example, think of bee stings in people. While most people find stings unpleasant, they are not dangerous. For sensitive people, a bee sting can be life-threatening.

Although relatively rare, vaccination reactions can occur, and the most common being similar to those in people-soreness at the injection site, mild lethargy and just not feeling quite up to par. These types of reactions usually resolve themselves within 24 hours.

Another type of reaction can cause hives and swelling of the face, most noticeable around the eyes, which may appear almost shut. It usually occurs a few to several hours after being vaccinated. These dogs are usually panting and agitated, because they are very itchy and uncomfortable. The biggest concern for pet owners is that the dog may be having trouble breathing. This is rarely the case but a logical conclusion because of the swelling, panting and general agitation. These reactions are relatively easy to treat, respond well and resolve fairly quickly.

The most serious and rarest of vaccine reactions is anaphylaxis. Pets who experience anaphylactic reactions usually do so almost immediately following the vaccination often while still in the veterinarian's office. These reactions are potentially life-threatening and must be treated immediately and aggressively. These pets usually vomit repeatedly, experience diarrhea which is often bloody and collapse, sometimes experiencing cardiac arrest. Most pets will recover with appropriate treatment. Again, these are very rare occurrences, which unfortunately cannot be predicted.