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Vaccination is a term coined by Edward Jenner for the process of administering a weakened form of a disease to patients as a means of giving them immunity to a more serious form of the disease. The word comes from the Latin for cow, in honor of the cowpox virus -- a relatively benign virus that was discovered to have the side effect of conferring immunity to smallpox, a deadly and highly contagious disease.

Since Jenner's time vaccination has become widespread and applicable to diseases other than smallpox. Louis Pasteur later developed the technique, extending it to protection against anthrax (caused by a type of bacterium) and rabies (caused by a virus) by treating the infectious agents for those diseases so that they lost their disease-producing abilities. In honour of Jenner's discovery, which his own work had built on, Pasteur adopted the name vaccine as a generic term for his these protective injections. Vaccination is now used to immunize people against many diseases.

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, cancer and Alzheimers disease vaccines.

See also: Timeline of vaccines, Allergy vaccination

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