Vaccination

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 the morbidity from infection. Vaccine efficacy 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; widespread immunity due to vaccination is largely responsible for the worldwide eradication of smallpox and the restriction of diseases such as polio, measles, tetanus from large areas of the world.

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., the outer coat proteins of a virus). Toxoids are produced for the immunization against toxin-based diseases, such as the modification of tetanospasmin toxin of tetanus to remove its toxic effect but retain its immunogenic effect.

Smallpox was likely the first disease people tried to prevent by purposely inoculating themselves with other types of infections, and was the first disease for which a vaccine was produced. The smallpox vaccine was designed in 1796 by the British physician Edward Jenner, although at least six people had used the same principles several years earlier. Louis Pasteur furthered the concept through his pioneering work in microbiology. The immunization was called vaccination because it was derived from a virus affecting cows (Latin: 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 it was eventually eradicated in 1979, it had killed an estimated 300–500 million people during the 20th century alone.

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 is used to refer to an immunization. Vaccination efforts have been met with some controversy since their inception, on scientific, ethical, political, medical safety, religious, and other 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 were undertaken, which greatly reduced the incidence of many diseases in numerous geographic regions.