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Vaccination is the administration of antigenic material (a vaccine) to stimulate an individual's immune system to develop adaptive immunity to a pathogen. Vaccines can prevent or ameliorate morbidity from infection. When a sufficiently large percentage of a population has been vaccinated, this results in herd immunity. The effectiveness of vaccination has been widely studied and verified; for example, the influenza vaccine, the HPV vaccine, and the chicken pox vaccine. Vaccination is the most effective method of preventing infectious diseases;〔 *United States Centers for Disease Control and Prevention (2011). (''A CDC framework for preventing infectious diseases.'' ) Accessed 11 September 2012. “Vaccines are our most effective and cost-saving tools for disease prevention, preventing untold suffering and saving tens of thousands of lives and billions of dollars in healthcare costs each year.” *American Medical Association (2000). (''Vaccines and infectious diseases: putting risk into perspective.'' ) Accessed 11 September 2012. “Vaccines are the most effective public health tool ever created.” *Public Health Agency of Canada. (''Vaccine-preventable diseases.'' ) Accessed 11 September 2012. “Vaccines still provide the most effective, longest-lasting method of preventing infectious diseases in all age groups.” *United States National Institute of Allergy and Infectious Diseases (NIAID). (''NIAID Biodefense Research Agenda for Category B and C Priority Pathogens.'' ) Accessed 11 September 2012. “Vaccines are the most effective method of protecting the public against infectious diseases.”〕 widespread immunity due to vaccination is largely responsible for the worldwide eradication of smallpox and the restriction of diseases such as polio, measles, and tetanus from much of the world. The World Health Organization (WHO) reports that licensed vaccines are currently available to prevent or contribute to the prevention and control of twenty-five preventable infections.〔World Health Organization, (Global Vaccine Action Plan 2011-2020. ) Geneva, 2012.〕 The active agent of a vaccine may be intact but inactivated (non-infective) or attenuated (with reduced infectivity) forms of the causative pathogens, or purified components of the pathogen that have been found to be highly immunogenic (e.g., outer coat proteins of a virus). Toxoids are produced for immunization against toxin-based diseases, such as the modification of tetanospasmin toxin of tetanus to remove its toxic effect but retain its immunogenic effect.〔(【引用サイトリンク】title=Tetanus )〕 Smallpox was most likely the first disease people tried to prevent by inoculating themselves and was the first disease for which a vaccine was produced. The smallpox vaccine was discovered in 1796 by the British physician Edward Jenner, although at least six people had used the same principles years earlier. Louis Pasteur furthered the concept through his work in microbiology. The immunization was called ''vaccination'' because it was derived from a virus affecting cows ((ラテン語:vacca—cow)).〔〔 Smallpox was a contagious and deadly disease, causing the deaths of 20–60% of infected adults and over 80% of infected children. When smallpox was finally eradicated in 1979, it had already killed an estimated 300–500 million people〔(【引用サイトリンク】title=UC Davis Magazine, Summer 2006: Epidemics on the Horizon )〕〔(How Poxviruses Such As Smallpox Evade The Immune System ), ScienceDaily, February 1, 2008〕 in the 20th century. In common speech, ''vaccination'' and ''immunization'' have a similar meaning. This distinguishes it from inoculation, which uses unweakened live pathogens, although in common usage either can refer to an immunization. Vaccination efforts have been met with some controversy on scientific, ethical, political, medical safety, and religious grounds. In rare cases, vaccinations can injure people and, in the United States, they may receive compensation for those injuries under the National Vaccine Injury Compensation Program. Early success and compulsion brought widespread acceptance, and mass vaccination campaigns have greatly reduced the incidence of many diseases in numerous geographic regions. ==Mechanism of function== Generically, the process of artificial induction of immunity, in an effort to protect against infectious disease, works by 'priming' the immune system with an 'immunogen'. Stimulating immune responses with an infectious agent is known as ''immunization''. Vaccination includes various ways of administering immunogens. Some vaccines are administered after the patient already has contracted a disease. Vaccines given after exposure to smallpox, within the first three days, are reported to attenuate the disease considerably, and vaccination up to a week after exposure probably offers some protection from disease or may modify the severity of disease. The first rabies immunization was given by Louis Pasteur to a child after he was bitten by a rabid dog. Subsequent to this, it has been found that, in people with uncompromised immune systems, four doses of rabies vaccine over 14 days, wound care, and treatment of the bite with rabies immune globulin, commenced as soon as possible after exposure, is effective in preventing the development of rabies in humans. Other examples include experimental AIDS, cancer and Alzheimer's disease vaccines. Such immunizations aim to trigger an immune response more rapidly and with less harm than natural infection. Most vaccines are given by hypodermic injection as they are not absorbed reliably through the intestines. Live attenuated polio, some typhoid, and some cholera vaccines are given orally to produce immunity in the bowel. While vaccination provides a lasting effect, it usually takes several weeks to develop, while passive immunity (the transfer of antibodies) has immediate effect.〔(【引用サイトリンク】title=Immunity Types )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Vaccination」の詳細全文を読む スポンサード リンク
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