Vaccination: Encyclopedia - Vaccination

Vaccination

Vaccination is a term coined by Edward Jenner for the process of administering live, albeit weakened, microbes to patients, with the intent of conferring immunity against a targeted form of a related disease agent. Vaccination (Latin: vacca—cow) is so named because the first vaccine was derived from a virus affecting cows: the cowpox virus, a relatively benign virus that, in its weakened form, provides a degree of immunity to smallpox, a contagious and deadly disease. In common speech, 'vaccination' and 'immunization' generally have the same colloquial meaning. Vaccination efforts were initially met with some resistance before early success brought widespread acceptance and mass vaccination campaigns were undertaken. The eradication of smallpox is considered the most spectacular success of vaccination. The last natural case of smallpox was discovered on October 26, 1977 in Somalia. This date is considered the anniversary of the eradication of smallpox.

Modern-day critics of vaccination are concerned that childhood vaccination plays a role in autoimmune disease and autism, though large-scale scientific studies have failed to find a link.

Vaccination - Triggering immune sensitization

In the generic sense, the process of triggering immune response, in an effort to protect against infectious disease, works by 'priming' the immune system with an 'immunogen'. Stimulating immune response, via use of an infectious agent, is known as immunization. Vaccinations involve the administration of one or more immunogens, in the form of live, but weakened (attenuated) infectious agents, which normally are either weaker, but closely-related species (as with smallpox and cowpox), or strains weakened by some process. In such cases, an immunogen is called a vaccine.

Some modern vaccines are administered after the patient already has contracted a disease, as in the cases of experimental AIDS, cancer and Alzheimer's disease vaccines. Vaccinia given after exposure to smallpox, within the first four days, is reported to attenuate the disease considerably, as vaccination within the first week is thought to be beneficial to a degree. The essential theory behind such immunizations is that the vaccine triggers superior immune response than the natural infection itself.

Vaccination - History of vaccinations

Vaccination campaigns have spread throughout the globe since Jenner's smallpox vaccine of 1796, sometimes prescribed by law or regulations. Vaccines are now used to fight a wide variety of disease threats besides smallpox. Louis Pasteur further developed the technique during the 19th century, extending its use to protecting against bacterial anthrax and viral rabies. The method Pasteur used entailed treating the infectious agents for those diseases so they lost the ability to cause serious disease. Pasteur adopted the name vaccine as a generic term in honor of Jenner's discovery, which Pasteur's work built upon.

Prior to vaccination with cowpox, the only known protection against 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 of that from natural infection with Variola, and the immunity provided was considered quite reliable. Factors contributing to the efficacy of variolation probably include the choices of Variola Minor strains used, the relatively low number of live viruses in the initial exposure, and the exposure route used, via the skin or nasal lining rather than inhalation of droplets into the lungs.

At the time, both vaccination and inoculation were condemned by the Protestant and Catholic churches.[1] Yale president Timothy Dwight IV held that vaccination thwarted God's will, saying:

British theologian Edward Massey published The Dangerous and Sinful Practice of Inoculation in 1772. Boston clergymen and devout physicians, believing that "the law of God prohibits the practice," formed the Anti-vaccination Society. Others held that the practice was unnatural and dangerous, going so far as to demand that doctors that carried out these procedures be tried for attempted murder.

In modern times, the first vaccine preventible disease targeted for eradication was smallpox. The World Health Organization coordinated the global effort to eradicate this disease. The last naturally occurring case of smallpox occurred in Somalia in 1977.

In 1988, the governing body of W.H.O. targeted polio for eradication by the year 2000. Although the target was missed, eradication is very close. The next eradication target would most likely be measles, which has declined since the introduction of measles vaccination in 1963.

In 2000, the Global Alliance for Vaccines and Immunizations, www.vaccinealliance.org, was established to strengthen routine vaccinations and introduce new and under-used vaccines in countries with GDP of under US$1000. GAVI is now entring its second phase of funding, which extends through 2014.

Vaccination - Herd immunity and medical risk management issues

Vaccination campaigns are generally accepted as having contributed to the worldwide elimination of smallpox, through herd immunity, and to the restriction of polio to isolated pockets in countries where healthcare access is difficult. The risk management practices of government health agencies' promoting widespread vaccination campaigns has prompted increasing controversy in recent years, despite the fact that many once-common childhood diseases, such as mumps, measles and rubella, are now relatively rare.

Nevertheless, vaccination campaigns may have unfortunate co-evolutionary side-effects, particularly if they produce a selective pressure in favor of certain strains against which there are no vaccines or treatment. Another problem related to co-evolution is that vaccines that may eliminate one infectious diseases or another may, in turn, 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, in theory, be to cause more deaths than before the vaccination was introduced. Potentially, this could be a 'perverse effect' of vaccination campaigns. Observation of immunity levels in a population over many years has been followed by booster immunization programs, for instance, in the United Kingdom, with measles and mumps.

Vaccination - Adjuvants and preservatives

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Vaccines typically contain one or more adjuvants, used to boost the immune response. They may also contain preservatives, which are used to prevent contamination with bacteria or fungi. Until recent years, the preservative thimerosal was used in many vaccines that did not contain live virus. As of 2005, the only childhood vaccine that contains thiomerosal is the influenza vaccine [2], which is currently only recommended for children with certain risk factors.^[3]

Adapted from the Wikipedia article "Vaccination", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki