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Health Issues Immunizations for Children Type of Issue: Children’s health, medical procedures, prevention, public health Definition: Exposure of a child to an infectious agent or chemical that confers resistance to that agent. The development of vaccines against specific infectious microbial agents resulted in the control or elimination of many diseases. Immunity to an antigen or disease may be induced using either of two methods. If preformed antibodies produced in another human or animal are inoculated into an individual, the result is passive immunity. Passive immunity can be advantageous in that the recipient achieves immunity in a short period of time. For example, if a person has been exposed to a toxin or has come into contact with an infectious agent, passive immunity can provide a rapid, short-term protection. Yet, since the individual does not generate the capacity to produce that antibody and the preformed antibodies are gradually removed from the body, no long-range protection is achieved. The stimulation of antibody production through exposure to antigens, such as those found in a vaccine, results in active immunity. Development of effective active immunity requires a time span of several days to several weeks. The immunity is long-term, however, often lasting for the life span of the individual. Furthermore, each additional exposure to that same antigen, either through a vaccine booster or through natural exposure, results in a more rapid, greater response than those achieved previously. Creating Vaccines The actual material utilized in a vaccine is variable. Attenuated organisms are mutants that have lost the ability to cause disease but that retain the antigenic character of the virulent strain. The most notable application of attenuation is the Sabin oral poliovirus vaccine (OPV). By testing hundreds of virus isolates for the ability to cause polio in monkeys, Albert Sabin was able to isolate certain strains that did not cause disease. These strains formed the basis for his vaccine. Similar testing resulted in the development of attenuated virus vaccines against a wide variety of agents, including those against measles, mumps, and rubella. In some cases, the isolation of attenuated strains of microorganisms has proved difficult. For this reason, inactivated or killed microorganisms often serve as the basis for vaccine production. The Salk inactivated poliovirus vaccine represents the best-known example. By treating poliovirus with a solution of the chemical formalin, Jonas Salk was able to inactivate the organism. The virus retained its antigenic potential and served as an effective vaccine. A similar process has resulted in vaccines to protect against other bacterial diseases, such as bubonic plague, cholera, and pertussis (whooping cough), and against viral influenza. In some cases, the vaccine is not directed against the etiological agent itself but against toxic materials produced by the agent, as with diphtheria and tetanus. The vaccines are produced by treating the diphtheria and tetanus toxins secreted by these bacteria with formalin. The toxoids that result are antigenically similar to the actual toxins and so are able to induce immunity. They are incapable, however, of causing the deleterious effects of the respective diseases. Only those determinants of a virus or bacterium that stimulate neutralizing antibodies are necessary in most vaccines. For this reason, the use of genetically engineered vaccines was begun in the 1980’s. The first example put into use was the production of a vaccine against the hepatitis B virus (HBV). The gene that encodes the surface antigen of HBV was isolated and inserted into a piece of genetic material within the yeast Saccharomyces. The HBV antigen produced by the yeast was purified and subsequently found to be as effective in a vaccine as the whole virus. Since no live virus is involved, there is no danger of an attenuated strain reverting to its virulent parent. Recently, similar technology has been applied to produce vaccines that protect against chickenpox and hepatitis A virus. Immunizing Against Major Childhood Diseases The most significant advancement in twentieth century health care in the United States has been the elimination of most major childhood diseases. In addition to poliovirus immunization, children routinely receive a variety of early immunizations. Measles, mumps, and rubella (MMR) vaccines are administered in a single preparation at fifteen months of age. All three contain live attenuated viruses. The measles vaccine was first introduced in 1966 and resulted in a decline in reported measles cases of nearly 99 percent by the 1980’s. Beginning about 1986, however, increasing numbers of cases of measles were reported among young adults who had been previously immunized. For this reason, the AAP recommends that children receive boosters of measles vaccine prior to entering high school, at approximately eleven to twelve years of age. A series of the diphtheria, pertussis, and tetanus (DPT) vaccine is administered at two, four, six, and eighteen months, with tetanus and diphtheria boosters recommended at ten-year intervals throughout the remainder of life. With the elimination of most other major childhood illnesses, Hemophilus influenzae type B infections moved into the dubious position of being among the most significant causes of illness and death among young children. In 1985, a vaccine developed from the outer coat of the bacterium was licensed for use. The vaccine worked poorly in children under the age of two, the major population at risk. Consequently, an improved vaccine was developed and licensed by 1987. The second vaccine consisted of a portion of the influenza coat joined to diphtheria toxoid. It was found to immunize children effectively at eighteen months of age; immunization with the vaccine is recommended by the age of fifteen months. By 1991, a total of nineteen vaccines had been licensed in the United States by the Food and Drug Administration (FDA) for uses in either children or adults. Aside from the eight previously described vaccines for children, eleven vaccines (five viral and six bacterial) are recommended for special circumstances. The use of genetic engineering, in which only the genes necessary to synthesize specific antigens are utilized, was first applied to the hepatitis B vaccine. It has recently been applied successfully to create vaccines against chickenpox and hepatitis A virus. A vaccine against hepatitis C virus is under development. This technology provides the potential for manufacturing vaccine “cocktails,” or combinations of such genes from a variety of infectious agents in a single vaccine. Richard Adler; updated by L. Fleming Fallon, Jr., M.D., M.P.H. See AlsoChildhood infectious diseases; Children’s health issues; Environmental health; Epidemics; Immunizations for the elderly; Influenza; Preventive medicine; Tuberculosis. For Further Information Bittle, J. L., and F. A. Murphy, eds. Vaccine Biotechnology. San Diego: Academic Press, 1989. A discussion of the use of techniques in molecular biology and genetic engineering in vaccine development. The style and depth of coverage is appropriate to anyone with basic knowledge of biology. @HG = Brock, Thomas D., ed. Microorganisms: From Smallpox to Lyme Disease. New York: W. H. Freeman, 1990. A collection of readings from Scientific American magazine. Included is a section on the role of vaccines in the prevention of disease, including their role in the elimination of smallpox. Also found are articles on synthetic vaccines and vaccination in Third World countries. Plotkin, Stanley A., and Edward Mortimer, Jr., eds. Vaccines. 3d ed. Philadelphia: W. B. Saunders, 1999. An excellent description of the role of vaccines in the prevention of disease. Begins with a history of immunization practices. Each subsequent chapter deals with a specific disease and the role and history of vaccine production in its prevention. While enough detail is provided to interest someone in the field, the text is appropriate for nonscientists. Roitt, Ivan. Essential Immunology. 9th ed. Boston: Blackwell Scientific Publications, 1997. An excellent textbook. Much of the book is detailed and requires some background in biology. Nevertheless, the chapters which deal with infection and immunization are clear and contain much that will interest nonscientists. Numerous graphs illustrate material from the text. |
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