Vaccination
Vaccination is a preventative health measure that can confer immunity to an infectious disease, without requiring that the vaccinated individual actually contracts the disease. Usually, this is carried out by innoculation with a vaccine, either a weakened form of the infectious agent (called a live vaccine) or a portion of the infectious agent, like an outer coat or internal proteins (called a killed vaccine) are introduced into the body of the individual to be protected. The immune system of that individual responds to the vaccine and, if that response is adequate, exposure to the germ will not result in sickness.
History of vaccination
"Edward Jenner vaccinated James Phipps in 1796 with cowpox obtained from a pustule on the hand of the milkmaid, Sarah Nelmes."[1] Later, he purposefully inoculated Phipps with a scab from a smallpox lesion. He did so having thought out a rational plan for why this act might confer protection, and, fortunately, Phipps did not contract the smallpox. Jenner went on to further investigate vaccination as a means to prevent disease, publishing his work, and so has become credited as the inventor of vaccination. However, other individuals used cowpox to inoculate family members against smallpox even before Jenner, and an understanding of the immunity conferred by infectious diseases to subsequent exposure can be traced back for at least 1500 years before Jenner's birth.
Variolation, the practice of inhalation of, or scarification with, dried and powdered smallpox pustules, had been in use since ad 1000 in China,later in the Middle East, and made popular in Europe in Jenner’s day by Lady Mary Wortley Montague (1689–1762).[1]
Classic references
Jenner E. An Inquiry Into the Causes and Effects of the Variolae Vaccinae, a Disease Discovered in Some of the Western Counties of England, Particularly Gloucestershire, and Known by the Name of the Cow Pox. London: Sampson Low, 1798.