Since Jenner's time vaccination has become widespread and applicable to diseases other than smallpox. Generically the process of protecting against an infectious disease by "priming" the immune system with material, the immunogen?, designed to stimulate an immune response to the infectious agent is known as immunization?. Vaccination is used where the immunogen is itself a living infectious agent, normally either a closely related bacterial species (as with smallpox and cowpox), or by using a strain weakened by some process. In this case the immunogen is called a vaccine.
In its greatest triumphs, vaccination campaigns have eliminated smallpox throughout the world and restricted polio? to some war-torn countries in Africa where health care access is difficult. Vaccines have made other once common childhood diseases rare, as mumps?, measles?, etc.
Some modern vaccines are administered after the patient already has the disease as in experimental AIDS and cancer vaccines.