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 fairly contagious disease that is sometimes deadly to humans. In common speech, 'vaccination' and 'immunization' generally have the same colloquial meaning.

Triggering immune sensitization

Generically speaking, 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 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.

History of vaccinations

Vaccination campaigns have spread throughout the globe since Jenner's time, often enforced by government mandate. 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.

Herd immunity and medical risk management issues

Vaccination campaigns are generally accepted as having contributed to the world wide elimination of smallpox, through herd immunity, and to the restriction of polio to isolated pockets in countries where health care 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 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 which 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, theoretically speaking, 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.

See also

• Evidence-based medicine
• Hyposensibilization (Allergy vaccination)
• Inoculation
• List of vaccine topics
• Timeline of vaccines
• Vaccine controversy
• Vaccine Adverse Event Reporting System

External links

• BMJJournals.com - 'MMR: Science and Fiction. Exploring the Vaccine Crisis; MMR and Autism: What Parents Need to Know' ('Rapid Responses' to book review), British Medical Journal

Sites promoting vaccination policies

• Brian Deer.com - 'mmr & autism investigation: part 1: the Lancet scandal', Brian Deer
• CDC.gov - 'National Immunization Program: leading the way to healthy lives', US Centers for Disease Control (CDC information on vaccinations)
• CDC.gov - 'Mercury and Vaccines (Thimerosal)', US Centers for Disease Control
• Immunize.org - Immunization Action Coalition' (nonprofit working to increase immunization rates)
• NYTimes.com - 'On Autism's Cause, It's Parents vs. Research', Gardiner Harris, Anahad O'Connor, New York Times (front page; June 25, 2005)
• ratbags.com - 'RatbagsDotCom: Home of the Ratbags on the Net'
• OpinionJournal.com - 'Autism and vaccines: Activists wage a nasty campaign to silence scientists' (unsigned editorial opinion), Wall Street Journal (February 16, 2004)
• SNHS.com - 'Anti-vaccine activists get jabbed', Michael Fumento (March 11, 2004)
• WHO.int - 'Immunizations, vaccines and biologicals: Towards a World free of Vaccine Preventable Diseases', World Health Organization (WHO's global vaccination campaign website)

Sites critical of vaccination policies

• 909Shot.com - 'National Vaccine Information Center: the oldest and largest national organization advocating reformation of the mass vaccination system'
• About.com - 'Killing the Messenger: Dr. Andrew Wakefield Fired', Floyd Tilton (December 5, 2001)
• VaccinationDebate.com - 'Vaccination Debate', Ian Sinclair
• whale.to - 'Vaccine Website'