Vaccination

# Overview
Vaccination is the administration of agent-specific, but relatively harmless, antigenic components that can induce protective immunity against the corresponding infectious agent in those individuals who are vaccinated. In practice, the terms vaccination and immunization are often used interchangeably. Vaccination is highly effective in the prevention of some particular infections. Vaccines are safe and are associated with minimal adverse reactions. Vaccination can prevent illness, disability, and death from vaccine-preventable diseases, which includes 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, though it does cause the immune system to produce T-lymphocytes and antibodies. Immunization currently prevents an estimated 2 to 3 million deaths every year. An additional 1.5 million deaths could be avoided, however, if global vaccination coverage is improved. An estimated 19.4 million infants worldwide are still missing out on basic vaccines. The material administered as a 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 for being perhaps the first person recorded to have been vaccinated with cowpox in order to artificially induce immunity to smallpox during 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 this principle 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 cowsthe relatively benign cowpox virus, which provides a degree of immunity to smallpox, a contagious and deadly disease. The World Health Organization coordinated the global effort to eradicate smallpox. The last naturally occurring case of smallpox occurred in Somalia in 1977.

# Vaccine-preventable diseases

# Classification

## Passive immunization
Passive immunization is a method of disease prevention that functions by transferring pre-made antibodies to a person at risk of acquiring a certain disease. This type of immunity could be acquired naturally during pregnancy, via 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, healthy people; it is a concentrated solution of antibodies, mainly IgG antibodies. Human immune globulin is given intra-muscularly (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 occurs, the more effective the 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 contains larger amounts of human immune globulin and is administered via the 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) is prepared for home-based use, especially for patients affected by primary immunodeficiency.

### Hyperimmune globulin
Hyperimmune globulin is derived from human plasma containing large amounts of antibodies. Those from whose plasma the globulin is derived are patients convalescing from natural infections or donors who are 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 one that is currently available is palivizumab, which is active against RSV.

## Active immunization

### 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. The vaccines 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 a 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.

# Adverse reactions
Adverse reactions to vaccines can be divided into 2 major groups:
- Allergic reactions
- Severe reportable reactions

## Allergic reactions
- Immediate reactions: Immediate reactions are IgE-related reactions that begins within minutes.
- Delayed reactions: Delayed reactions appear several hours or even days after administration and they are mostly non-IgE related reactions.

### Immediate reactions
Anaphylaxis is rare but important among immediate reactions. Health care providers should be aware of its symptoms and signs and be prepared for prompt treatment.
Other common but less serious immediate reactions include:
- Cutaneous symptoms: Flushing, itching, urticaria, and angioedema
- Respiratory symptoms: Nasal discharge, nasal congestion, change in voice quality, sensation of throat closure or choking, stridor, cough, wheeze, and dyspnea
- Cardiovascular symptoms: Faintness, syncope, altered mental status, palpitations, and hypotension

### Delayed reactions
Common delayed reactions to vaccines include:
- Fever: Fever is common after vaccination and should not preclude vaccination in the future.
- Local reactions: Local reactions such as swelling and erythema are common and can be treated with a cold compress.
- Serum sickness and serum sickness-like reactions

### Vasovagal reactions
Vasovagal reactions such as fainting, hypotension, pallor, diaphoresis, weakness, nausea, vomiting, bradycardia, and if severe, loss of consciousness may be seen after vaccination.

### Reaction to vaccine components
Vaccine components such as gelatin, egg proteins, cow's milk, thimerosal, aluminum, and phenoxyethanol that are used as vaccine preservatives, and they may cause adverse reactions ranging from fever or skin reactions to severe reactions that may require skin testing before future administration.

## Severe reportable reactions
Anaphylaxis or anaphylactic shock within seven days of any vaccine should be reported. Other vaccine-specific reactions that must be reported include:
- Tetanus: Brachial neuritis within 28 days
- Pertussis: Encephalopathy or encephalitis within seven days
- Measles, mumps, and/or rubella (MMR): Encephalopathy or encephalitis within 15 days
- Rubella: Chronic arthritis within six weeks
- Measles: Thrombocytopenic purpura within 7 to 30 days; vaccine-strain measles infection in an immunodeficient recipient within six months of measles vaccination
- Oral polio: Paralytic polio or vaccine-strain polio within 30 days to 6 months (this vaccine is no longer used for routine childhood immunization)
- Rotavirus: Intussusception within 30 days of rotavirus immunization