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Overview

Vaccination is the administration of agent-specific, but relatively harmless, antigenic components that in vaccinated individuals can induce protective immunity against the corresponding infectious agent. In practice, the terms vaccination and immunization are often used interchangeably. Vaccination is highly effective to prevent some particular infections. Vaccines are safe with minimal adverse reactions. vaccination can prevents illness, disability and death from vaccine-preventable diseases including cervical cancer, diphtheria, hepatitis B, measles, mumps, pertussis, pneumonia, polio, rotavirus diarrhea, rubella and tetanus. Vaccines help develop immunity by imitating an infection. This type of infection, however, does not cause illness, but it does cause the immune system to produce T-lymphocytes and antibodies. Immunization currently averts an estimated 2 to 3 million deaths every year. An additional 1.5 million deaths could be avoided, however, if global vaccination coverage improves. An estimated 19.4 million infants worldwide are still missing out on basic vaccines. The material administrated as vaccine, 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.
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 (vacca in latin means cow) is so named because the first vaccine was derived from a virus affecting cow, the relatively benign cowpox virus, which provides a degree of immunity to smallpox, a contagious and deadly disease which, the World Health Organization coordinated the global effort to eradicate this disease. The last naturally occurring case of smallpox occurred in Somalia in 1977.

Vaccine preventable diseases

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

Classification

Immunization

Passive

Active (vaccination)

Human immune globulin (IG)

Hyperimmune globulin

Monoclonal antibodies

­Live, attenuated vaccines

Inactivated vaccines

Toxoid vaccines

Subunit vaccines

Conjugate vaccines

IV immune globulin (IVIG)

Subcutaneous immune globulin (SCIG)

Passive immunization

Passive immunization is a method of disease prevention by transferring pre-made antibodies to a person at risk of acquiring a certain disease. Although, this type of immunity could be acquired naturally , during pregnancy by trans-placental maternal antibodies' transfer to the fetus. Artificial passive immunization is normally given by pre-made immunoglobulins to a person at risk of acquiring a certain disease.

Human immune globulin (IG)

Human immune globulin is obtained from normal persons and is a concentrated solution of antibodies mainly, IgG antibodies. Human immune globulin is given intra-muscular (IM). Up to 48 hours is required for IGs to reach the maximum serum concentration and their half-life is about 3 weeks. The sooner administration the more effective prevention. IGs only provide temporary protection. Diseases with available human immune globulins include:

• Hepatitis A
• Measles
• Immunoglobulin deficiency
• Varicella (in immunocompromised patients when varicella-zoster IG is unavailable)
• Rubella exposure during the 1st trimester of pregnancy

IV immune globulin (IVIG)

IV immune globulin contains larger amounts of human immune globulin and it administers via IV route. Diseases that may be prevented or ameliorated by using IVIGs include:

• Kawasaki disease
• HIV infection in children
• Chronic B-cell lymphocytic leukemia
• Primary immunodeficiencies
• Immune thrombocytopenia
• Prevention of graft-vs-host disease

Subcutaneous immune globulin (SCIG)

Subcutaneous immune globulin (SCIG) is prepared for home based use especially for persons affected by primary immunodeficiency.

Hyperimmune globulin

Hyperimmune globulin is derived of a person's plasma containing large amounts of antibodies. These persons are whom convalescing from natural infections or donors artificially immunized. Hyperimmune globulins are available for cytomegalovirus, varicella-zoster, hepatitis B, infant botulism, rabies, and tetanus.

Monoclonal antibodies

Specific monoclonal antibodies can be used against infections. The only current available is, palivizumab which is active against RSV.

­Live attenuated vaccines

Live attenuated vaccines are produced by modifying a disease-producing (wild) virus or bacterium in a laboratory. The resulting vaccine organism retains the ability to replicate and produce immunity, but usually does not cause illness. These vaccines are produced by growing the virus in tissue cultures that will select for less virulent strains, or by mutagenesis or targeted deletions in genes required for virulence. Attenuated vaccines can not be used by immunocompromised individuals. Examples of live attenuated vaccines include measles, mumps, and rubella vaccine (MMR) and varicella (chickenpox) vaccine.

­Inactivated vaccines

These vaccines are made by inactivating or killing the pathogen (mostly, viruses). The inactivated polio vaccine is an example of this type of vaccine.

Toxoid vaccines

Toxoid vaccines are effective against bacteria that produces toxins and they are weakened toxins, produced by particular bacteria. The DTaP vaccine contains diphtheria and tetanus toxoids.

­Subunit vaccines

­Subunit vaccines contain only some parts of bacteria or virus not the entire germ. Because these vaccines contain only the essential antigens and not all the other molecules that make up the germ, side effects are less common. The pertussis component of the DTaP vaccine is an example of a subunit vaccine.

­Conjugate vaccines

­Conjugate vaccines are effective against bacteria that have polysaccharides in their cell wall components. Polysaccharides may cause less stimulation of immune system and result in defective immune response. Conjugate vaccines are effective for these types of bacteria because they connect (or conjugate) the polysaccharides to antigens that the immune system responds to very well. This linkage helps the immature immune system react to the coating and develop an immune response. An example of this type of vaccine is the Haemophilus influenzae type B (Hib) vaccine.