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vaccine
A preparation given to induce immunity against an infectious disease. A vaccine works by sensitizing the body's immune system to a particular disease-causing bacterium, bacterial toxin, or virus. If the particular infectious agent invades the body at a later time, the sensitized immune system quickly produces antibodies, which help destroy either the agent itself or the toxin it produces.
Types of vaccine
Most vaccines are preparations containing the organisms (or parts of the organisms) against which protection is sought. So that these organisms themselves do not cause disease, they are killed or weakened. The term "live attenuated organisms" describes strains of organisms that have been rendered harmless. Attenuation is achieved either by artificially altering their genes or by successively infecting laboratory animals, thus producing small changes in the organisms which considerably reduce the ability of the organisms to cause disease without reducing their ability to induce immunity. Other vaccines contain chemically modified bacterial toxins. Again, modification removes the dangerous qualities of he toxin without affecting the immune features.
Vaccines are now available to protect against a wide variety of infectious disease. Examples of live attenuated vaccines are those given to protect against measles, mumps, and rubella (MMR), yellow fever, and poliomyelitis. Diphtheria and tetanus vaccines contain inactivated bacterial toxins. Cholera, typhoid fever, pertussis, rabies, and influenza vaccines contained killed organisms. Hepatitis B vaccine is now produced by genetic engineering.
Administration of vaccines
Vaccines are usually given by injection into the upper arm. Oral polio vaccine is given on a sugar lump or by drops on the tongue. Some vaccines require several doses, spaced some weeks apart; others require only one dose. The effectiveness of vaccines varies from near total protection in most cases, to only partial or weak protection (for example, against typhoid fever or cholera). The duration of effectiveness also varies from a few months to lifelong.
Related categories
• HEALTH AND DISEASE
• MICROBIOLOGY
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