How do vaccines work?

Vaccines contain portions of bacteria or viruses, or even a weak strain of the actual virus. These small doses enable the body to build immunity to the disease without actually contracting it. The immune system then has the ability to remember that disease, should it encounter the same germ again, and fight it off without having to build immunity from scratch. From early times ancient people have understood that if a person survived a disease, they were unlikely to contract it again. However it took the genius of Edward Jenner in 1796, to create the basis of the immunization industry today. He rubbed cowpox pus onto cuts in the arm of a small boy. The boy remained healthy when he was later exposed to smallpox.