The use of bacterial or viral components to stimulate the body to produce infection-fighting substances. Immunizations are sometimes called vaccinations. Immunizations consist of either a weakened strain of the entire virus/bacteria or parts of the bacteria or virus. They stimulate a healthy immune system to recognize the bacteria or virus, and then produce antibodies which destroy the bacteria or virus preventing future infection. Most immunizatons require a series of shots in order to be effective. Some vaccines also require a booster injection many years after the original series of vaccinations. There is information on each specific immunization under its respective name.