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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. Vaccination (Latin: vacca—cow) is so named because the first vaccine was obtained from cows: 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 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 species (as with smallpox and cowpox), or by using a strain weakened by some process. In this case the immunogen is called a vaccine. Prior to vaccination with cowpox, the only known protection againt smallpox was inoculation or variolation (Variola - the Smallpox viruses) where a small amount of live smallpox virus was administered to the patient; this carried the serious risk that with too high a dose the patient would be killed or seriously ill. The death rate from variolation was reported to be around a tenth that from natural infection with Variola, and the immunity provided to be quite reliable. Factors probably include the selection of Variola Minor cases to derive the innocula from, the relatively low number of live viruses in the initial exposure compared to exposure to an infectious case directly, and the route via the skin or nasal lining rather than inhalation of droplets into the lungs. In common speech, "vaccination" and "immunization" are usually used as having the same broad meaning.

In a great triumph for public health and scientific medicine, vaccination campaigns have eliminated smallpox throughout the world and restricted polio to some war-torn countries in Africa where health care access is difficult. Widespread vaccination programs have made other once common childhood diseases such as mumps, measles and rubella rare.

However, vaccination programmes might have unfortunate effects if they produce a selective pressure in favour of certain strains against which there is no vaccination, and for which there may be no treatment. A related problem is that vaccines eliminating some infectious diseases may allow others to thrive in the ecological niche that has been vacated. For example, it has been postulated that (the less often fatal) serogroup B meningitis strains may expand into the niche provided if serogroup C is largely eradicated through vaccination. However, while there has been a rise in serogroup B meningitis, there is as yet no evidence to link this to the meningitis C vaccination.

An incompletely successful attempt at eradication of a disease through vaccination might increase the average age of contraction of the disease. In diseases such as measles, where there is a higher rate of complication in older people, the overall effect might be to cause more deaths than before the vaccination was introduced. This is a perverse effect of vaccination. Observation of immunity levels in a population over many years has been followed by booster immunisation programmes for instance in the UK with Measles and Mumps.

Some modern vaccines are administered after the patient already has the disease as in experimental AIDS, cancer and Alzheimers disease vaccines. Vaccinia given after exposure to Smallpox, within the first 4 days is reported to attentuate the disease considerably, and within the first week to be beneficial to a degree. The essential here is that the vaccine is more immunogenic than the natural infection, or that the live vaccine produces infection and therefore response more quickly than the disease will.

In the United States, the government indemnifies physicians and manufacturers against legal risks associated with vaccination, and provides a compensation scheme which avoids the court system.

See also: Timeline of vaccines, Hyposensibilization (Allergy vaccination)

External links

Sites promoting vaccines

Anti-vaccination sites

Last updated: 06-02-2005 13:05:58
Last updated: 09-12-2005 02:39:13