What are Immunizations (Vaccinations)?
Vaccines are biological products that stimulate the immune system to make protective proteins – called antibodies – against different pathogens, such as viruses and bacteria. They work by presenting examples of these viruses and bacteria to special cells in the body can recognize and from which use to produce the correct antibody. To do this without actually causing the disease, either a modified or killed version or a reproduction of the specific part of the pathogen that is recognized, is used in the vaccine.
What is a “vaccine reaction”?
A “vaccine reaction” occurs when the immune system of the animal “over reacts” to the vaccine. This is called a hypersensitivity reaction. There are several types of hypersensitivity reactions:
- Anaphylaxis – this is the most severe form of reaction to an immunizing agent. It occurs immediately after the immunization is given and is a medical emergency necessitating immediate treatment. Many times true anaphylactic reactions are fatal in spite of appropriate treatment.
- Type I Hypersensitivity – This form of hypersensitivity occurs usually within a few hours of administration of a vaccine – sometimes sooner. The symptoms are usually moderate in terms of morbidity, but are generally not fatal.
- Type IV Hypersensitivity – Another name for this form is a “delayed” hypersensitivity. This form doesn’t occur until several days after a vaccine is given and symptoms are generally mild.
How to know and What to do if you think your animal is experiencing a “reaction”
Symptom | Reason | What to do |
| Collapse | Symptom of anaphylaxis if occurs within minutes of vaccine | Seek care immediately |
| Difficulty breathing | Can occur with anaphylaxis or type I reactions | Call or seek care immediately |
| Vomiting and/or Diarrhea | Usually results from type I reactions | Call for care instructions |
| Lethargy | Can be a normal response to immunization. | If persists for more than 24 hours – Call for care instructions. If accompanies other symptoms follow instructions for those symptoms. |
| Skin alterations | Discoloration or hives can be a result of type I or IV hypersensitivity reactions | Call for care instructions |
| Firm mass that occurs at injection site within 3 weeks of immunization | Likely a benign fibrous inflammatory nodule. Monitor and if increases in size call for care instructions. |