aRT Iv The Immune System in Health and Disease CLINICAL FOCUS Vaccination Challenges in the such as the contention that vaccines U.S. and Developing Countries countered by correct information from trusted sources to retreat from our progress in immunization by noncom- recently of a causal relationship between pliance will return us to the age when eviously common vaccination and autism, a condition of measles, mumps, whooping cough, and childhood diseases are seldom seen in unknown etiology. Most such reports polio were part of the risk of growing up the United States, a testament to the ef- are based solely on the coincidental tim- Children in the developing world suf- fectiveness of vaccination. A major bar- ing of vaccination and onset of disease, fer from a problem different from those rier to similar success in the rest of the or on limited sampling and poor statisti- in the United States. Examination of in- world is the difficulty of delivering vac. cal analyses. So far, no alleged asso- fant deaths worldwide shows that exist- cines to all children. However, even at ciations have withstood scrutiny that ing vaccines could save the lives of home the U.S. is becoming a victim of included large population samples and millions of children. As seen in the table, its own success. Some parents who acceptable statistical methods. there are safe, effective vaccines for five have never encountered diseases now While children in this country are pro- of the top ten killers of children. Al nearly vanquished in the U.S. do not tected against a variety of once-deadly though the list of diseases in the table in consider it important to have their in- diseases, this protection depends on cludes HIV, TB, and malaria, for which fants vaccinated or they may be lax in continuation of our immunization pro- no vaccines are available, administration adhering to recommended schedules of grams. Dependency on herd immunity is of the vaccines that are recommended immunization. Others hold the unin. dangerous for both the individual and for infants in the United States could cut formed belief that the risks associated society. Adverse reactions to vaccines child mortality in the world by approxi- with vaccination outweigh the risk of in- must be examined thoroughly, of course, mately half fection. This flawed reasoning is fueled and if a vaccine causes unacceptable What barriers exist to the achievement by periodic allegations of linkage be- side reactions, the vaccination program of worldwide vaccination and complete tween vaccination and various disor- must be reconsidered. At the same time, eradication of many childhood diseases? ders, such as the report circulating anecdotal reports of disease brought on The inability to achieve higher levels of Genetic engineering techniques can be used to develop vac- do not cause disease or with antigenic components from the cines to ze the immune response to selected epitopes pathogens. This section describes current usage of passive and to delivery of the vaccines. This chapter de- and active immunization techniques scribes the vaccines now in use and describes vaccine strate- gies, including experimental designs that may lead to the Passive Immunization Involves transfer vaccines of the future of Preformed Antibodies Jenner and Pasteur are recognized as the pioneers of vaccina tion, or induction of active immunity, but similar recogni- Active and Passive Immunization tion is due to Emil von Behring and Hidesaburo Kitasato for their contributions to passive immunity. These investigators Immunity to infectious microorganisms can be achieved by were the first to show that immunity elicited in one animal active or passive immunization In each case, immunity can can be transferred to another by injecting it with serum from be acquired either by natural pr from mother to fetus or by previous infection by the organ Passive immunization, in which preformed antibodies are ism)or by artificial means such as injection of antibodies or transferred to a recipient, occurs naturally by transfer of ma- vaccines(Table 18-1, on page 416). The agents used for in- ternal antibodies across the placenta to the developing fetus ducing passive immunity include antibodies from humans or Maternal antibodies to diphtheria, tetanus, streptococci, animals, whereas active immunization is achieved by inocu- rubeola, rubella, mumps, and poliovirus all afford pa lation with microbial pathogens that induce immunity but sively acquired protection to the developing fetus. Maternal414 PART IV The Immune System in Health and Disease recently of a causal relationship between vaccination and autism, a condition of unknown etiology. Most such reports are based solely on the coincidental tim￾ing of vaccination and onset of disease, or on limited sampling and poor statisti￾cal analyses. So far, no alleged asso￾ciations have withstood scrutiny that included large population samples and acceptable statistical methods. While children in this country are pro￾tected against a variety of once-deadly diseases, this protection depends on continuation of our immunization pro￾grams. Dependency on herd immunity is dangerous for both the individual and society. Adverse reactions to vaccines must be examined thoroughly, of course, and if a vaccine causes unacceptable side reactions, the vaccination program must be reconsidered. At the same time, anecdotal reports of disease brought on by vaccines, and unsupported beliefs, such as the contention that vaccines weaken the immune system, must be countered by correct information from trusted sources. To retreat from our progress in immunization by noncom￾pliance will return us to the age when measles, mumps, whooping cough, and polio were part of the risk of growing up. Children in the developing world suf￾fer from a problem different from those in the United States. Examination of in￾fant deaths worldwide shows that exist￾ing vaccines could save the lives of millions of children. As seen in the table, there are safe, effective vaccines for five of the top ten killers of children. Al￾though the list of diseases in the table in￾cludes HIV, TB, and malaria, for which no vaccines are available, administration of the vaccines that are recommended for infants in the United States could cut child mortality in the world by approxi￾mately half. What barriers exist to the achievement of worldwide vaccination and complete eradication of many childhood diseases? The inability to achieve higher levels of Many previously common childhood diseases are seldom seen in the United States, a testament to the ef￾fectiveness of vaccination. A major bar￾rier to similar success in the rest of the world is the difficulty of delivering vac￾cines to all children. However, even at home the U.S. is becoming a victim of its own success. Some parents who have never encountered diseases now nearly vanquished in the U.S. do not consider it important to have their in￾fants vaccinated or they may be lax in adhering to recommended schedules of immunization. Others hold the unin￾formed belief that the risks associated with vaccination outweigh the risk of in￾fection. This flawed reasoning is fueled by periodic allegations of linkage be￾tween vaccination and various disor￾ders, such as the report circulating CLINICAL FOCUS Vaccination: Challenges in the U.S. and Developing Countries Genetic engineering techniques can be used to develop vac￾cines to maximize the immune response to selected epitopes and to simplify delivery of the vaccines. This chapter de￾scribes the vaccines now in use and describes vaccine strate￾gies, including experimental designs that may lead to the vaccines of the future. Active and Passive Immunization Immunity to infectious microorganisms can be achieved by active or passive immunization. In each case, immunity can be acquired either by natural processes (usually by transfer from mother to fetus or by previous infection by the organ￾ism) or by artificial means such as injection of antibodies or vaccines (Table 18-1, on page 416). The agents used for in￾ducing passive immunity include antibodies from humans or animals, whereas active immunization is achieved by inocu￾lation with microbial pathogens that induce immunity but do not cause disease or with antigenic components from the pathogens. This section describes current usage of passive and active immunization techniques. Passive Immunization Involves Transfer of Preformed Antibodies Jenner and Pasteur are recognized as the pioneers of vaccina￾tion, or induction of active immunity, but similar recogni￾tion is due to Emil von Behring and Hidesaburo Kitasato for their contributions to passive immunity. These investigators were the first to show that immunity elicited in one animal can be transferred to another by injecting it with serum from the first (see Clinical Focus, Chapter 4). Passive immunization, in which preformed antibodies are transferred to a recipient, occurs naturally by transfer of ma￾ternal antibodies across the placenta to the developing fetus. Maternal antibodies to diphtheria, tetanus, streptococci, rubeola, rubella, mumps, and poliovirus all afford pas￾sively acquired protection to the developing fetus. Maternal