The purpose of vaccination or immunization is to intentionally expose the human immune system to a foreign infectious agent so that it forms a memory of that agent. In future infections by that organism, the attack against the agent will take only minutes to hours, and the agent will be destroyed before it has a chance to inflict its damage.

Passive immunization refers to injection of prepared antibodies into a person who has either already been infected or is at risk of acquiring an infection. In this case the infected person’s immune system is not actively protecting the body, hence the name passive immunization. Examples of passive immunization include Rabies and Hepatitis A.

Types of Vaccines

Vaccines are of two general types:

1. In live attenuated vaccines, the organism in the vaccine is alive but unable to infect a person with a normal immune system. Patients with impaired immunity-such as those with immune deficiencies, on chemotherapy for cancer, or with AIDS-and pregnant women must not be given live vaccines. Examples of live attenuated vaccines are measles, mumps, rubella, and oral polio.
2. Inactivated or killed vaccines contain dead, but intact, organisms, so the immune system can still recognize them. Most vaccines are inactivated.

Vaccines are usually given at multiple intervals because the immune system needs several reminders to "boost" immunity. Specific vaccines are available for the following infections:

Diphtheria

Disease: Diphtheria is a bacterial illness acquired through inhalation of infected particles. It causes a severe sore throat and possibly heart and nerve damage. The bacteria live in the airways of healthy or recovering humans.
Vaccine: DTP
Interval: 2-, 4-, 6-, and 15 months and 5 years of age.

Pertussis

Disease: A bacterial illness acquired through inhalation of the infected particles. It causes severe, life-threatening coughing spells (whooping cough), and possibly seizures and brain damage. The bacteria usually live in the airways of adults with no or minimal cough.
Vaccine: DTP
Interval: 2-, 4-, 6-, and 15 months and 5 years of age.

Tetanus

Disease: Tetanus is a bacterial infection acquired through dirty wound infection. Tetanus causes severe and painful muscle contractions. The bacteria are abundant in the soil.
Vaccine: DTP
Interval: 2-, 4-, 6-, and 15 months, 5 years of age. The vaccine must be repeated every 10 years.

Polio

Disease: Polio is a viral infection involving the mouth and throat, and later the blood and spinal cord. Approximately 10% of the infected people develop spinal cord infection, causing muscle paralysis, usually one-sided.
Vaccine: OPV (oral=live) and Injected (inactivated); inactivated vaccine is given to children with immunodeficiencies.
Interval: 2-, 4-, 6-, and 18 months and 5 years of age.

Measles

Disease: Measles is a viral infection acquired through breathing infected particles. It causes rash, croupy cough, pneumonia, diarrhea, and possibly brain infection and bleeding.
Vaccine: MMR
Interval: 15 months and 12 years.

Mumps

Disease: Mumps is a viral infection acquired through breathing infected particles. It causes painful swelling of the Parotid gland, testes, and pancreas gland.
Vaccine: MMR
Interval: 15 months and 12 years.

Rubella (German Measles)

Disease: Rubella is a viral infection acquired through inhalation of infected particles. It causes rash, fevers, and enlarged lymph nodes. If a pregnant woman becomes infected, the fetus could be severely and permanently damaged.
Vaccine: MMR
Interval: 15 months and 12 years.

Haemophilis influenza type b (Hib)

Disease: Haemophilis influenza type b is a bacterial infection acquired through inhalation of infected particles or through contact with infected objects. It causes life-threatening conditions such as meningitis (infection of the lining of the brain), throat swelling, and joint infection.
Vaccine: Hib
Interval: 2-, 4-, 6-, and 15 months

Influenza Virus

Disease: Influenza is a viral infection of the upper- and lower respiratory tract. It can be fatal in people with heart, lung, and other chronic diseases.
Vaccine: Flu shot; recommended for patients with heart and lung disease and residents of nursing homes and long-term care facilities.
Interval: yearly

Pneumococcal pneumonia

Disease: Pneumococcal pneumonia is a bacterial illness causing pneumonia.
Vaccine: Pneumococcal vaccine; recommended for people with heart, lung, or other chronic illnesses.
Interval: Every ten years.

Also available, based on specific circumstances, are vaccines for the following:

Varicella-Zoster (Chickenpox): Varicella-Zoster is a viral infection acquired through inhalation of infected particles. It causes painful blistering and later crusty rash and fevers. Rare complications include infections of the brain, joints, and kidneys and/or hemorrhaging. Vaccination is recommended for children with immunodeficiencies, but it is safe and frequently given to healthy children.

Hepatitis B: Hepatitis B is a viral infection of the liver. It is acquired through exposure to blood (such as in a transfusion), through sexual intercourse, and from a mother to her fetus. Vaccination is recommended in high-risk patients, especially the health care providers.

Cholera: Cholera is a bacterial infection of the small intestine. It causes severe watery diarrhea and dehydration that could lead to death. The vaccine is recommended for travelers to Africa, Middle East, and the Far East.

Plague: Plague is a bacterial infection carried by rodents. It causes fever, skin sores, enlarged lymph nodes, and if not treated, death. Humans are accidentally infected by fleas that feed off the infected rodents. The vaccine is recommended for people traveling to or working in areas where plague is prevalent.

Typhoid fever: Typhoid is a bacterial infection caused by Salmonella. It causes diarrhea, fevers, and if left untreated, death. The vaccine is recommended for travelers to Africa, South America, the Middle East, and the Far East.

Rabies: Rabies is a viral infection acquired through the bite of an infected mammal. It causes fevers, headaches, restlessness, seizures, coma, and death. Immunization is passive by injection of anti-Rabies antibodies.

Lyme Disease: Lyme Disease is a bacterial infection acquired through the bite of a tick that feeds on deer. It causes rash, fever, and, left untreated, possible neurological or heart damage. Vaccination is recommended to those who live in areas where deer population is large and in contact with the human population.

For More Information

• Centers For Disease Control and Prevention (CDC): Advisory committee on Immunization Practices (www.cdc.gov).
• American Academy of Pediatrics (www.aap.org).
• Infectious Diseases Society of America (www.idsociety.org)