But before symptoms you still have it so it's not only for preventing disease. Vaccines are used to teach/modify your immune system to fight something. Whether

But before symptoms you still have it so it's not only for preventing disease. Vaccines are used to teach/modify your immune system to fight something. Whether you have it or not is not part of the definition[0]. [0] a substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from the causative agent of a disease, its products, or a synthetic substitute, treated to act as an antigen without inducing the disease.