Vaccination (vak-sih-NAY-shun) is a way of producing immunity * to a specific disease by introducing into a person's body an inactive, altered, or weakened form of a microorganism * , which provokes an immune response.
Before the 19th century, a dangerous disease known as smallpox killed millions of people throughout the world. All of that was soon to change as the result of an observation made by Edward Jenner (1749–1823), an English country doctor, in 1796. Jenner reported that milkmaids who milked cows infected with a disease known as cowpox did not contract smallpox. Instead, the milkmaids had a mild case of a similar rash-producing disease. Jenner concluded that cowpox must somehow have protected these milkmaids against the smallpox infection.
Although Jenner is credited with discovering the principles of immunization and developing the first vaccine against smallpox, men and women had grasped or intuited the principles of immunization for at least several thousand years before him. There are historical accounts of successful vaccinations against contagious illnesses in ancient Greece, India, and China. In England, approximately 75 years before Jenner's pioneering work, Lady Mary Wortley Montagu (1689–1762), wife of the British ambassador to the Ottoman Empire, vigorously promoted the practice of variolation (administering material from smallpox lesions to healthy people to produce immunity to smallpox). Montagu had observed this practice while living in what later became Turkey. She studied the method of Turkish women, who for centuries had collected in walnut shells the fluid from lesions of persons with smallpox and used lancets to press this material into the skin of healthy people to protect them from the disease. Back in England, she enthusiastically promoted this method and witnessed its many successes.
As an experiment, Jenner extracted material from the blister-like lesions of persons with cowpox and placed this material into healthy people. Jenner deliberately gave people the mild cowpox infection, which was an experiment with vaccination. He discovered that the body's natural defense system can be stimulated to become protective against a specific illness after having been ill with a similar and more benign *
After Jenner's time, scientists developed many effective vaccines, including ones against poliomyelitis * , measles * (rubeola), diphtheria * , and pertussis * . Overall, these vaccinations prevented disease and saved hundreds of millions of lives.
Vaccines, the preparations used in vaccinations, stimulate the body's immune response by mimicking the substances that cause disease. Small amounts of antigenic material (the vaccines themselves) are administered by oral ingestion or injection (usually intramuscular injection). Vaccines mimic a natural infection without actually causing disease. The antigenic substances promote immunologic memory, whereby specialized cells of the immune system become memory cells. This means they are able to recognize and respond to any substance that bears the same antigen * (if and when the actual disease-causing agent enters the body). When a person's immune system * can respond rapidly and effectively to an infection that is just beginning, so that it cannot spread and cause damage within the body, that person is considered as having resistance to the infectious agent.
Booster vaccinations are second (or subsequent) vaccinations, separated from the first or prior vaccination by certain periods (often a span of several years) that result in an upsurge in or an extension of the effectiveness of the original vaccinations. Booster vaccinations take advantage of immunologic memory. When the white blood cells that have the ability to recognize and respond to a particular antigen are exposed to that antigen as part of a booster vaccination, those abilities are strengthened and reinforced. Some vaccinations require booster doses, whereas others do not.
Vaccinations protect more people than just the individuals who receive them. They also protect unvaccinated people who live around those who have been vaccinated, a concept known as herd immunity. A vaccination protects a person from contracting and then spreading an infection. When enough people living in an area have been immunized, the relevant disease-causing agent will have difficulty spreading in that area because it cannot find new human hosts * . The disease is much less likely to be passed on, even to those few people who remain unvaccinated. It is estimated that the protection of unvaccinated people in a community occurs when the proportion of persons in that community who are vaccinated reaches 95 percent.
Vaccinations boost immunity through a so-called active process, meaning that the immune system, in responding to an antigen, is reacting actively. There is also passive immunity, which is immunity acquired through the transfer of antibodies * * and, after birth, from the mother's breast milk to the infant. A mother who has immunity against tetanus, a disease of the central nervous system caused by the toxin secreted by the tetanus bacterium, for example, will pass this immunity along to the developing fetus through the transfer of antibodies while she is pregnant. However, the offspring's immunity is only temporary. The infant's passive immunity disappears a few months after birth. Infants later make their own antibodies after being exposed to an infectious agent or receiving a vaccine.
Vaccinations are one of the great success stories of public health programs in the 20th century. Widespread use of vaccines has brought about dramatic reductions in illness, disability, and death from many diseases, including potentially deadly and disabling childhood diseases such as diphtheria, tetanus, pertussis (whooping cough), measles, and poliomyelitis. Before measles vaccination began in the United States in 1963, for example, an estimated 500,000 cases and 500 measles-associated deaths in the United States were reported each year, according to the Centers for Disease Control and Prevention (CDC). After immunizations began, these statistics dropped sharply. The United States had been averaging from 90 to 100 cases of measles each year, but the number of cases began increasing in the 2010s, with 189 reported cases in 2015. This is due partly to children being exempt from vaccinations for religious and other personal reasons.
In the 1920s, before vaccination for diphtheria was available, approximately 150,000 cases of diphtheria occurred annually in the United States. Diphtheria is a frightening and painful disease. The thick mucus * produced in the throat and nasal passages in the course of the disease closes the airway and can lead to suffocation. After the introduction of diphtheria vaccine, millions of people were protected from this disease. Because of diphtheria vaccination, the illness became virtually nonexistent in developed nations.
Poliomyelitis, a viral disease characterized by inflammation of nerve cells in the brain and spinal cord, otherwise known as polio and infantile paralysis, was a health scourge in the United States until the 1950s. The virus can spread along nerve fiber pathways, damaging and even destroying motor neurons (especially the motor neurons that supply muscles in the legs). This damage to nerve tissue often produces muscle weakness and paralysis * . The virus may damage neurons that supply the chest-wall muscles and the diaphragm, a thin sheet of muscle separating the chest from the abdomen that is essential to breathing. Paralysis of these muscles can lead to respiratory failure * and death.
Smallpox is the only disease that has been eradicated entirely from the global population through an aggressive international immunization program. This highly contagious disease once killed as many as one out of every three infected individuals. The last case of smallpox in the United States was in 1949. The last naturally occurring case in the world was in Somalia in 1977. After the World Health Organization declared in 1980 that the disease had been eliminated from the world, routine vaccination against smallpox among the general public was stopped because it was no longer necessary for prevention. However, since smallpox is considered a weapon of bioterrorism, the U.S. government is taking precautions in the event of a smallpox outbreak.
The 20th century saw both tremendous successes of vaccines and advances in vaccine technology. Some earlier vaccines were improved, and new vaccines were introduced. There are four different types of vaccines available:
Vaccine preparations are produced by drug manufacturers and in the United States must be approved for use and licensed by the Food and Drug Administration (FDA). Vaccines are also patented, which diminishes their availabilities.
A vaccination schedule is a list of recommended vaccines that includes the recommended timings of all vaccine doses. Vaccination schedules are compiled by the Advisory Committee on Immunization Practices (ACIP), a 15-member panel that advises the CDC and the U.S. Department of Health and Human Services (HHS). Vaccines are usually administered during early childhood, although some vaccinations may need to be given later in life.
The ACIP and the CDC recommend vaccinations. For the general population (including the general pediatric population), vaccinations are recommended but not mandated. In the United States all 50 states require children to be immunized against measles, diphtheria, Haemophilus influenzae type B, poliomyelitis, and rubella in order to enroll in day care and/or public school.
Currently the CDC recommends the following vaccines for children six years of age or younger:
The CDC recommends the following vaccines for adolescents 11 to 18 years old:
In addition to children and adolescents, adults require vaccines. For example, adults generally need a tetanus booster vaccination every 10 years, and older adults or adults with some medical conditions are advised to get a flu shot every year. Adults who did not undergo immunization as children, those who have emigrated from a country where vaccines are not readily available, and those who travel to areas where there is a higher risk of certain infectious diseases also receive vaccinations.
Vaccines against tetanus and rabies *
Vaccinations have been proven to drastically reduce the incidence and mortality rates of many diseases and to eradicate (eliminate) some diseases from entire populations. Still, some parents are reluctant to vaccinate their children for a variety of reasons. Some parents feel that children receive too many vaccines and that the administration of vaccines begins too early. Others worry about possible adverse reactions. Still others believe that with lower rates of certain diseases in the United States, regular vaccinations are no longer necessary.
A dramatic example proves otherwise. The United Kingdom, Japan, and Sweden cut back their use of pertussis vaccine in the 1970s when some medical experts in those countries believed that the risks of using it outweighed the benefits. Between 1971 and 1979, the United Kingdom experienced more than 100,000 cases of the disease and 36 pertussisrelated deaths. From 1974 to 1979, Japan's vaccination coverage in the general population dropped from 80 percent to 20 percent, during which time the annual number of pertussis cases rose from a low of 393 and no deaths to an epidemic * high of 13,000 cases and 41 deaths. In Sweden, the annual incidence of pertussis per 100,000 children up to age six leaped from 700 in 1981 to 3,200 in 1985.
Another common belief is that vaccines cause the infectious diseases that they are intended to protect against. In fact, killed vaccines or those made from only a component of the infectious agent, such as a protein, cannot cause the infectious disease. In addition, continual efforts are made by the manufacturers of vaccines to minimize the possibility of contracting disease from a live vaccine. For example, in January 2000 the ACIP recommended that the polio vaccine be switched from an attenuated oral version to a killed vaccine to reduce or eliminate whatever risk there was of contracting vaccine-associated paralytic polio. Although the live oral vaccine was largely responsible for ridding the United Sates of polio, it caused polio in one of every 1.4 million people who received their first dose of the vaccine. The killed version cannot cause polio.
Even though vaccinations prevent many cases of serious, and even fatal, illness, any vaccine can have side effects, and many people experience them after receiving vaccines. Potential side effects for vaccines can include low-grade fever; mild pain, tenderness, and redness at the site of the injection; rash; and irritability. Less common, but more serious, reactions include seizures * * , sudden infant death syndrome * (SIDS), and brain damage have not been proven and remain debated.
Vaccination provides the best protection against many well-known childhood diseases, and preventing the spread of these diseases is vital to public health. Vaccines protect the people who receive them, and they also prevent the spread of disease to people who have not been vaccinated. Modern science has produced many effective vaccines. In 2006 the FDA approved the first vaccine for adult shingles, a painful viral disease caused by viral infection of nerve endings in skin. International travel and a rapidly shrinking globe mean that diseases can easily cross national and continental lines. Diseases once rarely seen in one country can easily be imported from another. This fact makes receiving vaccinations an ongoing necessity. If people somehow start to believe that they or their children do not need to get vaccinated or if they depend on others to get vaccinated, overall vaccination levels will drop. This could lead to the return of diseases that are easily prevented by vaccination.
In the early 21st century, medical researchers were continuing to work to develop vaccines for a wide range of diseases, including HIV * /AIDS * . The quest for an HIV/AIDS vaccine was complicated by the fact that HIV mutates (changes) rapidly (leading to the existence of a large number of distinct viral subspecies) and because HIV damages the very cells that are needed by the body in any response to an antigen. Malaria vaccines were also the subject of intensive research. Several drug manufacturers were continuing to work on the development of vaccines that will protect against tuberculosis infection.
In general such research takes years and is costly. Because almost all vaccinations carry some risk, an important part of their development is to assess how effective they are and whether the benefits of a new vaccine outweigh those risks.
See also AIDS and HIV Infection • Bioterrorism Agents: Overview • Chickenpox (Varicella) • Diphtheria • German Measles (Rubella) • Hepatitis • Human Papillomavirus (HPV) • Immune System and Other Body Defenses: Overview • Influenza • Measles (Rubeola) • Meningitis • Mumps • Pneumonia • Poliomyelitis • Rabies • Sexually Transmitted Infections (STIs): Overview • Shingles (Herpes Zoster) • Tetanus (Lockjaw) • Whooping Cough (Pertussis)
Conis, Elena. Vaccine Nation: America's Changing Relationship with Immunization. Chicago: University of Chicago Press, 2015.
Centers for Disease Control and Prevention. “HPV Vaccines: Vaccinating Your Preteen or Teen.” http://www.cdc.gov/hpv/parents/vaccine.html (accessed March 4, 2016).
Centers for Disease Control and Prevention. “Immunization Schedules.” http://www.cdc.gov/vaccines/schedules/index.html (accessed March 4, 2016).
Centers for Disease Control and Prevention. “Smallpox Disease Overview.” http://www.bt.cdc.gov/agent/smallpox/overview/disease-facts.asp (accessed March 4, 2016).
MedlinePlus. “Immunization.” U.S. National Library of Medicine. https://www.nlm.nih.gov/medlineplus/immunization.html (accessed March 4, 2016).
National Institute of Allergy and Infectious Diseases. “Vaccines.” (accessed March 4, 2016).
U.S. Food and Drug Administration. “Vaccines for Children —A Guide for Parents and Caregivers.” http://www.fda.gov/BiologicsBloodVaccines/ResourcesforYou/Consumers/ucm345587.htm (accessed March 4, 2016).
Vaccines.gov . “Guide to Federal Immunization Web Sites.” http://www.vaccines.gov/more_info/guide/index.html (accessed March 4, 2016).
World Health Organization. “Vaccines.” http://www.who.int/topics/vaccines/en/ (accessed March 4, 2016).
Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329-4027. Toll-free: 800-232-4636. Website: http://www.cdc.gov (accessed March 4, 2016).
Immunization Action Coalition. 2550 University Ave. W, Suite 415 North, Saint Paul, MN 55114. Telephone: 651-647-9009. Website: http://www.immunize.org (accessed March 4, 2016).
National Vaccine Information Center. 21525 Ridgetop Cir., Suite 100, Sterling, VA 20166. Telephone: 703-938-0342. Website: http://www.nvic.org (accessed March 4, 2016).
World Health Organization. Ave. Appia 20, 1211 Geneva 27, Switzerland. Telephone: 41 22 791 21 11. Website: http://www.who.int (accessed March 4, 2016).
* immunity (ih-MYOON-uh-tee) is the condition of being protected against an infectious disease. Immunity often develops after a germ has entered the body. One type of immunity occurs when the body makes special protein molecules called antibodies to fight the disease-causing germ. The next time that germ enters the body, the antibodies quickly attack it, usually preventing the germ from causing disease.
* microorganism is a tiny organism that can be seen only by using a microscope. Types of microorganisms include fungi, bacteria, and viruses.
* benign (beh-NINE) refers to a condition that is not cancerous or serious and will probably improve, go away, or not get worse.
* poliomyelitis (po-lee-o-my-uhLYE-tis) is a condition caused by the polio virus that involves damage of nerve cells. It may lead to weakness and deterioration of the muscles and sometimes paralysis.
* measles (ME-zuls) a viral respiratory infection that is best known for the rash of large, flat, red blotches that appear on the arms, face, neck, and body.
* diphtheria (dif-THEER-e-uh) is an infection of the lining of the upper respiratory tract (the nose and throat). It is a disease that can cause breathing difficulty and other complications, including death.
* pertussis (per-TUH-sis), or whooping cough, is a bacterial infection of the respiratory tract that causes severe coughing.
* antigen (AN-tih-jen) is a substance that is recognized as a threat by the body's immune system, which triggers the formation of specific antibodies against the substance.
* immune system (im-YOON) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.
* hosts are organisms that provide another organism (such as a parasite or virus) with a place to live and grow.
* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.
* fetus (FEE-tus) is the term for an unborn human after it is an embryo, from nine weeks after fertilization until birth.
* mucus (MYOO-kus) is a thick, slippery substance that lines the insides of many body parts.
* paralysis (pah-RAH-luh-sis) is the loss or impairment of the ability to move some part of the body.
* respiratory failure is a condition in which breathing and oxygen delivery to the body are dangerously altered. This may result from infection, nerve or muscle damage, poisoning, or other causes.
* mumps is a contagious viral infection that causes inflammation and swelling in the glands of the mouth that produce saliva.
* rubella (roo-BEH-luh) is a viral infection that usually causes a rash and mild fever.
* influenza (in-floo-EN-zuh), also known as the flu, is a contagious viral infection that attacks the respiratory tract, including the nose, throat, and lungs.
* cirrhosis (sir-O-sis) is a condition that affects the liver, involving long-term inflammation and scarring, which can lead to problems with liver function.
* meningitis (meh-nin-JY-tis) is an inflammation of the meninges, the membranes that surround the brain and the spinal cord. Meningitis is most often caused by infection with a virus or a bacterium.
* sepsis is a potentially serious spreading of infection, usually bacterial, through the bloodstream and body.
* diabetes (dye-uh-BEE-teez) is a condition in which the body's pancreas does not produce enough insulin or the body cannot use the insulin it makes effectively, resulting in increased levels of sugar in the blood. This can lead to increased urination, dehydration, weight loss, weakness, and a number of other symptoms and complications related to chemical imbalances within the body.
* sickle cell disease is a hereditary condition in which the red blood cells, which are usually round, take on an abnormal crescent shape and have a decreased ability to carry oxygen throughout the body.
* rabies (RAY-beez) is a viral infection of the central nervous system that usually is transmitted to humans by the bite of an infected animal.
* epidemic (eh-pih-DEH-mik) is an outbreak of disease, especially infectious disease, in which the number of cases suddenly becomes far greater than usual. Usually, epidemics are outbreaks of diseases in specific regions, whereas widespread epidemics are called pandemics.
* seizures (SEE-zhurs) are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.
* autism (AW-tih-zum) is a developmental disorder in which a person has difficulty interacting and communicating with others and usually has severely limited interest in social activities.
* sudden infant death syndrome, or SIDS, is the sudden death of an infant less than a year old that is not explained even after an autopsy or examination of the death scene. Most cases occur while the otherwise well baby is asleep on its stomach.
* HIV, or human immunodeficiency (ih-myoo-no-dih-FIH-shensee) virus, is the virus that causes AIDS (acquired immunodeficiency syndrome).
* AIDS, or acquired immunodeficiency (ih-myoo-no-dih-FIHshen-see) syndrome, is an infection that severely weakens the immune system. It is caused by the human immunodeficiency virus (HIV).