Immunization

A child being immunized against polio.

Immunization (or immunisation in British English) is the process of conferring increased resistance to an infectious disease by a means other than experiencing the natural infection. Typically, this involves exposure to an agent (antigen or immunogen) that is designed to fortify the person's immune system against that agent or similar infectious agents (active immunization). Immunization also can include providing the subject with protective antibodies developed by someone else (passive immunization).

The term immunization often is used interchangeably with vaccination and inoculation, all of which use a viable infecting agent. Like active immunization, vaccination involves administration of antigenic material to produce immunity to a disease, which will prevent or ameliorate the effects of infection by a pathogen. This material can either be live, but weakened forms of pathogens (such as bacteria or viruses); killed or inactivated forms of these pathogens; or purified material such as proteins. While vaccination is used today in the same sense as immunization, in a strict sense the term refers to its original meaning, which is protection conferred against smallpox by material taken from cow infected with Cowpox virus, which is related to the vaccinia virus (Blakemore and Jennett 2001). While inoculation can be used synonymously for immunization in common use, it is often limited to the an active immunization process involving unweakened, live pathogents. The term inoculation is used less frequently nowadays (Blakemore and Jennett 2001).

When the human immune system is exposed to a disease once, it can develop the ability to quickly respond to a subsequent infection. Therefore, by exposing an individual to an immunogen in a controlled way, the person's body will then be able to protect itself from infection later on in life.

History of immunization

While Dr. Edward Jenner (1749-1823) has been recognized as the first doctor to give sophisticated immunization, it was British dairy farmer Benjamin Jestey who noticed that "milkmaids" did not become infected with smallpox, or displayed a milder form. Jestey took the pus from an infected cow's udder and inoculated his wife and children with cowpox, thereby making them immune to smallpox.

By injecting a human with the cowpox virus (which was harmless to humans), Jenner swiftly found that the immunized human was then also immune to smallpox. The process spread quickly, and the use of cowpox immunization has led to the almost total eradication of smallpox in modern human society. After successful vaccination campaigns throughout the 19th and 20th centuries, the World Health Organization (WHO) certified the eradication of smallpox in 1979.

Smallpox was the first disease people tried to prevent by purposely inoculating themselves with other types of infections: Smallpox inoculation was started in China before 200 B.C.E. In 1718, Lady Mary Wortley Montague reported that the Turks have a habit of deliberately inoculating themselves with fluid taken from mild cases of smallpox and she inoculated her own children. In 1796 Edward Jenner inoculated using cowpox (a mild relative of the deadly smallpox virus). Pasteur and others built on this.

Benjamin Jesty is notable as perhaps the first person recorded to have vaccinated with cowpox in order to artificially induce immunity to smallpox in the epidemic of 1774. The term vaccination was first used by Edward Jenner an English physician 22 years later in 1796. Louis Pasteur further adapted in his pioneering work in microbiology. Vaccination (Latin: vacca—cow) is so named because the first vaccine was derived from a virus affecting cows—the relatively benign cowpox virus—which provides a degree of immunity to smallpox, a contagious and deadly disease.

Required immunizations upon entry to school

In the USA each state provides school districts with an obligation to regulate those eligible to enter public schooling. Since schools are congregate settings, and thus communication of diseases is a consideration, school districts may exclude children who seek to attend without the protection of certain immunizations.

For example, in the state of Ohio, USA, each student is required to provide proof of specific immunizations or have an authorized waiver from the requirement upon entry to school at age 6 years. If a student does not have the necessary immunizations or a waiver acceptable to the state, the school principal may refuse entry and require compliance with a set deadline. This procedure is for the safety of all students and follows Ohio State law.

Unless given a waiver, students must meet the following requirements:

1. DPT (Diphtheria, pertussis, tetanus)—Five doses if the fourth one was before the fourth birthday.
2. Measles—Two doses, the first one after 12 months of age, and the second at least 28 days after the first birthday.
3. Rubella—Same as measles.
4. Mumps—Same as measles.
5. Polio—Four doses if the third was before the fourth birthday.
6. Hepatitis B—For students starting kindergarten.

Additionally, for schools offering a pre-school program, add the requirements for two doses of haemophilus influenzae.

Passive and active immunization

Passive immunization

Passive immunization is where pre-made antibodies are given to a person. This method of Immunization begins to work very quickly, but it is short lasting, because the antibodies are naturally broken down, and not stored for later use. It can also result in serum sickness and anaphylaxis.

Passive immunization can be naturally acquired when antibodies are being transferred from mother to fetus during pregnancy, to help protect the fetus before and shortly after birth.

Artificial passive immunization is normally given by injection and is used if there has been a recent outbreak of a particular disease or as an emergency treatment to poisons from insects etc. The antibodies are normally produced in animals and injected into humans.

Active immunization

Active immunization is where the actual microbe is taken in by a person. Antibodies are created by the recipient and are stored permanently.

Active immunization can occur naturally when an untreated microbe is received by a person who has not yet come into contact with the microbe and has no pre-made antibodies for defense. The immune system will eventually create antibodies for the microbe, but this is a slow process and, if the microbe is deadly, there may not be enough time for the antibodies to begin being used.

Artificial active immunization is where the microbe is injected into the person before they are able to take it in naturally. The microbe is treated, so that it will not harm the injected person. Depending on the type of disease, this technique also works with dead microbes, parts of the microbe, or treated toxins from the microbe.

See also

• Flu vaccine
• H5N1 flu vaccine clinical trials
• Vaccine controversy
• Expanded Program on Immunization (Philippines)

External Links

• National Network for Immunization Information (NNii)
• Centers for Disease Control National Immunization Program

Vaccination/Vaccine (and Immunization, Inoculation. See also List of vaccine topics and Epidemiology)

Development: Models - Timeline - Toxoid - Trial Administration: ACIP - GAVI - VAERS - Vaccination schedule - VSD Specific vaccines: Anthrax - BCG - Cancer - DPT - Flu - HIV - HPV - MMR - Pneumonia - Polio - Smallpox Controversy: A-CHAMP - Anti-vaccinationists - NCVIA - Pox party - Safe Minds - Simpsonwood - Thimerosal controversy - Vaccine injury

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