Wednesday, October 15, 2008

Vaccination

Vaccination is the inoculation of a person (or animal) in order to bring about immunity to an infection (pathogenic) organism. The term (from the Latin Vacca, “cow”) originally meant immunization against smallpox, because the procedure originated in 1796 the milkmaids who had contracted the mild disease cowpox (vaccinia) were immune to smallpox. The development of cowpox has since led to the production of vaccines against a wide range of diseases.

Vaccination is bases on the ability of a person’s immune system to respond much more effectively and rapidly to a microorganism the second or third time that the elements of the immune system encounter the invading organism. It was in this way, for example, that the milk maids immune system were “primed” by the cowpox virus to respond effectively to the closely related smallpox virus.

A vaccine may consist of living organisms that are weakened or attenuated, in a laboratory so that they create immunity but do not cause disease. It may also consist of related organisms that cause a similar but milder disease, of killed organisms, or of extracts of the organisms that can induce the desired immune response and subsequent immunity but do not cause the disease. Periodic booster immunization is recommended with most vaccines, because the immunity caused by the initial inoculation may decrease with time. The time interval before booster shots are required varies greatly with the type of vaccine.

Vaccination has occasional complications. Thus patients with a poorly functioning immune system have particular problems with certain vaccines. Immunodeficient patients may develop acute poliomyelitis from the attenuated virus vaccine, for example, although they do not develop the disease from killed polio virus. Transient problems with mild fevers, muscle aches, and tenderness at the inoculation site are also common to many vaccines. Control of serious disease by vaccination, however, is usually worth such risks.

Most of the exceptionally effective vaccines are viral vaccine, such as those for measles, mumps, and rubella. Influenza vaccines are recommended for individuals at high risk for serious infections of the lungs. Because influenza strains are different almost every year, vaccination should be carried out yearly in the susceptible population. Vaccination for yellow fever and certain types of hepatitis are also of proven efficacy. Also available are vaccines for certain bacterial infections, such as typhoid fever, cholera, diphtheria, whooping cough, and tetanus. Among new vaccines being developed are vaccines against malaria, leprosy, and dengue fever. Researchers are also exploring the production of multipurpose vaccines though genetic engineering using entitles such as the vaccinia virus or the bacterium known as BCG to carry genes from several disease organisms.

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