What Is a Vaccine?

Vaccines are commonly administered to pets in their first two years of life, or following rescue, for the purpose of protecting them against certain viruses. What is a vaccine? It's an altered form of the virus that protects pets from catching it.

How Vaccines Are Made

Vaccines are made by altering a virus, such as feline immunodeficiency virus (FIV), in a lab, producing one of three types of vaccines.

  1. A killed vaccine, which contains a specific number of dead virus cells. These are essentially empty shells that still trigger immune response, but cannot reproduce.
  2. A modified live vaccine, which contains an altered virus that will reproduce, but can no longer cause an associated disease.
  3. A recombinant vaccine, which contains specific components of a virus organism, called antigens. Scientists determine which piece of the virus produces the best immune response and isolate that part to make a vaccine.

Each of these types of vaccine triggers an immune response in pets; their immune systems produce the antibodies necessary to fight off that specific virus. The goal of vaccination is that if an animal is exposed to that virus in the future, his immune system will be prepared to kill it before it can cause a serious medical condition.

Some vaccines will cause your pet to become mildly symptomatic over a short term. This is standard, and not cause for concern unless the pet does not recover quickly.

Vaccines for Dogs

Core vaccines for dogs (those that should be given to every dog) include distemper, parvovirus, rabies and hepatitis. Non-core vaccines (those recommended for only certain dogs) include lyme, coronavirus, letospirosis, bordetella, parainfluenza and measles.

Vaccines for Cats

Core vaccines for cats include panleukopenia, rhinotracheitis, calicivirus and rabies. Non-core vaccines include feline leukemia, chlamydia, infectious peritonitis, bordetella, giardia and FIV. Cats that spend time outdoors or are exposed to other cats that spend time outdoors should receive the feline leukemia vaccine.

Vaccination Pros and Cons

The type and number of vaccinations recommended for your pet depend on your pet's age, health, breed and likelihood of exposure to various viruses. The rabies vaccine is legally required for all pets. Many vaccines must be administered more than once to build up or maintain immunity.

Puppies and kittens typically receive combination vaccines (those that inoculate against multiple viruses) every few weeks over the course of their first year. After that, many vaccinations are given yearly or every three years for the duration of a pet's life, or until it is deemed unnecessary. Some pet owners choose to stop vaccinating after the first two or three years of their pet's life.

Most vaccines cause a mild reaction that may mirror symptoms of the contained virus. Some cause allergic reactions in some pets. Killed vaccines in particular are more likely to cause an allergic reaction; they contain chemicals designed to improve immune response and usually have higher numbers of virus particles per dose than other types of vaccines. Some pets have more severe vaccine responses and develop long-term health problems. Ultimately, type and regularity of vaccination is a pet owner's decision.