Immunization

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A child being immunized against polio.

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List of terms related to Immunization

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Immunization, or immunisation, is the process by which an individual is exposed to an agent that is designed to fortify his or her immune system against that agent. The material is known as an immunogen. Immunization is the same as inoculation and vaccination in that inoculation and vaccination use a viable infecting agent like immunization does. 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, their 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 and 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.

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)

Diseases and vaccines

A vaccination schedule is a recommended series of vaccinations including the suggested timing of all doses. A vaccine is an antigenic preparation used to produce active immunity to a disease, in order to prevent or reduce the effects of infection by any natural or 'wild' pathogen. Many vaccines require multiple doses for maximum effectiveness, either to produce sufficient initial immune response or to boost response that fades over time. Vaccine schedules are developed by governmental agencies or physicians groups to achieve maximum effectiveness using required and recommended vaccines for a locality while minimizing the number of health care system interactions. Over the past two decades, the recommended vaccination schedule has grown rapidly and become more complicated as many new vaccines have been developed.

Some vaccines are recommended only in certain areas (countries, subnational areas or at-risk populations) where a disease is common. For instance, yellow fever vaccination is on the routine vaccine schedule of French Guiana, is recommended in certain regions of Brazil but in the United States is only given to travellers heading to countries with a history of the disease. In developing countries, vaccine recommendations also have to consider poor health care access, high vaccine cost and issues with vaccine availability and storage. Sample vaccinations schedules discussed by the World Health Organization show a developed country using a schedule which extends over the first five years of a child's life and uses vaccines which cost over $700 including administration costs while a developing country uses a schedule providing vaccines in the first 9 months of life and costing only $25. This difference incorporates the facts that health care costs are much lower, many vaccines are provided at lower costs to developing nations and more expensive vaccines, often for less common diseases, are not utilized.

In 1900, the smallpox vaccine was the only one administered to children. By the 1960s, children routinely received five vaccines, for protection against (diphtheria, pertussis, tetanus, polio, and smallpox), and as many as eight shots by two years of age. As of 2007, the US Centers for Disease Control (CDC) now recommends vaccination against at least sixteen diseases. By two years of age, U.S. children receive as many as 24 vaccine injections, and might receive up to five shots during one visit to the doctor. The use of combination vaccine products means that, as of 2006, the United Kingdom immunisation programme consists of just 11 injections by the age of two years and a further three injections by the time of leaving school.

Characteristics of diseases vaccinated against in most vaccine schedules

	Disease		Worldwide		U.S.		U.K.
	Transmission	Incubation	Incidence	Deaths	Incidence	Deaths	Incidence	Deaths
Diphtheria	Saliva	1-4 days	30,000	3,000	1	0	0	0
Haemophilus influenzae	By airborne droplet	1-4 days	2-3,000,000	450,000 (mostly children)	1,743	7	30	0
Hepatitis B	Exchange of bodily fluids	6 weeks - 6 months	5,700,00 (acute)	521,000	7,996	7	600	Not reported
Measles	Airborne	10-12 days	30-40,000,000	610,000	44	0	77	1
Mumps	Airborne droplets	14-21 days	477,079 (reported)	N/A	270	1	16,436	0
Pertussis	Airborne droplets	5-10 days	39,000,000	297,000	9,771	18	2	2
Polio	Fecal contamination	Hours	1,951	<1,000	0	0	0	0
Rubella	Airborne droplets	5-7 days	Not reported	631,571 (most CRS)	18	(1 CRS)	0	0
Tetanus	Penetrating injury, blood contamination,	3-10 days	18,781	200,000	25	5	6	0
Tuberculosis	Airborne	3 day - 15 weeks	8,000,000	1,600,000	15,056	784	6,572	373
Varicella	Airborne	2 weeks	Not reported	Not reported	22,841	32	Not reported	Not reported

A typical childhood vaccination schedule for infants in developing countries with Yellow Fever

Vaccine	Age at immunization	Notes
BCG	Birth
Polio	6, 10 and 14 weeks	At birth, in endemic countries
Diphtheria, Tetanus, Pertussis	6, 10 and 14 weeks
Hepatitis B	6, 10 and 14 weeks	Vaccine not widely available.
Haemophilus influenzae	6, 10 and 14 weeks	Vaccine not widely available.
Yellow Fever	9 months	In countries where Yellow Fever poses a risk.
Measles	9 months	A second vaccination should be provided.

External links

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

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