418 PART IV The Immune System in Health and Disease Multiple immunizations with the polio vaccine are required to ensure that an adequate immune response is generated to each of the three strains of poliovirus that make up the Paralytic polio cases Recommendations for vaccination of adults deper 1952 the risk group. Vaccines for meningitis, pneumonia, and in fluenza are often given to groups living in close quarters(e.g Pertussis military recruits) or to individuals with reduced immunity 934 (e.g, the elderly). Depending on their destination, interna tional travelers are also routinely immunized against such endemic diseases as cholera, yellow fever, plague, typhoid, hepatitis, meningitis, typhus, and polio. Immunization against the deadly disease anthrax had been reserved fo Measles workers coming into close contact with infected animals or 1941 products from them. Recently, however, suspected use of anthrax spores by terrorists or in biological warfare has widened use of the vaccine to military personnel and civil- ians in areas at risk of attack with this deadly agent Vaccination is not 100% effective. With any vaccine, a ∮」ssmauperentageorepentwilrspondpolandthere problem if the majority of the population is immune to an Number of reported cases infectious agent. In this case, the chance of a susceptible ndividual contacting an infected individual is so low that FIGURE 18-1 Reported annual number of cases of rubella(Ger. the susceptible one is not likely to become infected. This man measles), polio, pertussis(whooping cough), mumps, measles, phenomenon is known as herd immunity. The appearance of and diphtheria in the United States in the peak year for which data are measles epidemics among college students and unvaccinated available (orange)compared with the number of cases of each dis- preschool-age children in the United States during the mid- ease in 1999(green). Currently, vaccines are available for each of these to late 1980s resulted partly from an overall decrease in vac- diseases, and vaccination is recommended for all children in the cinations, which had lowered the herd immunity of the pop United States. Data from Centers for Disease Control. l ulation(Figure 18-2). Among preschool-age children, 88% of those who developed measles were unvaccinated. Most of the college students who contracted measles had been vacci nated as children, but only once; the failure of the single dence of whooping cough, with 7405 cases in 1998. The re- of passively acquired maternal antibodies that reduced their cent development of an acellular pertussis vaccine that is as overall response to the vaccine. The increase in the incidence effective as the older vaccine, but with none of the side ef- of measles prompted the recommendation that children fects, is expected to reverse this trend receive two immunizations with the combined measles- As indicated in Table 18-3, children typically require mumps-rubella vaccine, one at 12-15 months of age and the nultiple boosters(repeated inoculations) at appropriately second at 4-6 years timed intervals to achieve effective immunity In the first The Centers for Disease Control( CDc) has called atten months of life the reason for this may be persistence of cir- tion to the decline in vaccination rates and herd immunity lating maternal antibodies in the young infant. For exam- among American children. For example, a 1995 publication ple, passively acquired maternal antibodies bind to epitopes reported that in California nearly one-third of all infants are on the DPt vaccine and block adequate activation of the im- unvaccinated and about half of all children under the age of mune system; therefore, this vaccine must be given several 2 are behind schedule on their vaccinations. Such a decrease times after the maternal antibody has been cleared from an in herd immunity portends serious consequences, as illus- infant's circulation in order to achieve adequate immunity. trated by recent events in the newly independent states of the Passively acquired maternal antibody also interferes with the former Soviet Union. By the mid-1990s, a diphtheria epi effectiveness of the measles vaccine; for this reason, the demic was raging in many regions of these new countries, MMR vaccine is not given before 12-15 months of age. In linked to a decrease in herd immunity resulting from de Third World countries, however, the measles vaccine is ad- creased vaccination rates after the breakup of the soviet are still present, because 30% hough maternal antibodies Union. This epidemic, which led to over 157,000 cases of ministered at 9 months 50% of young children in diptheria and 5000 deaths, is now controlled by mass immu these countries contract the disease before 15 months of age. nization programsMultiple immunizations with the polio vaccine are required to ensure that an adequate immune response is generated to each of the three strains of poliovirus that make up the vaccine. Recommendations for vaccination of adults depend on the risk group. Vaccines for meningitis, pneumonia, and in￾fluenza are often given to groups living in close quarters (e.g., military recruits) or to individuals with reduced immunity (e.g., the elderly). Depending on their destination, interna￾tional travelers are also routinely immunized against such endemic diseases as cholera, yellow fever, plague, typhoid, hepatitis, meningitis, typhus, and polio. Immunization against the deadly disease anthrax had been reserved for workers coming into close contact with infected animals or products from them. Recently, however, suspected use of anthrax spores by terrorists or in biological warfare has widened use of the vaccine to military personnel and civil￾ians in areas at risk of attack with this deadly agent. Vaccination is not 100% effective. With any vaccine, a small percentage of recipients will respond poorly and there￾fore will not be adequately protected. This is not a serious problem if the majority of the population is immune to an infectious agent. In this case, the chance of a susceptible individual contacting an infected individual is so low that the susceptible one is not likely to become infected. This phenomenon is known as herd immunity. The appearance of measles epidemics among college students and unvaccinated preschool-age children in the United States during the mid￾to late 1980s resulted partly from an overall decrease in vac￾cinations, which had lowered the herd immunity of the pop￾ulation (Figure 18-2). Among preschool-age children, 88% of those who developed measles were unvaccinated. Most of the college students who contracted measles had been vacci￾nated as children, but only once; the failure of the single vac￾cination to protect them may have resulted from the presence of passively acquired maternal antibodies that reduced their overall response to the vaccine. The increase in the incidence of measles prompted the recommendation that children receive two immunizations with the combined measles￾mumps-rubella vaccine, one at 12–15 months of age and the second at 4–6 years. The Centers for Disease Control (CDC) has called atten￾tion to the decline in vaccination rates and herd immunity among American children. For example, a 1995 publication reported that in California nearly one-third of all infants are unvaccinated and about half of all children under the age of 2 are behind schedule on their vaccinations. Such a decrease in herd immunity portends serious consequences, as illus￾trated by recent events in the newly independent states of the former Soviet Union. By the mid-1990s, a diphtheria epi￾demic was raging in many regions of these new countries, linked to a decrease in herd immunity resulting from de￾creased vaccination rates after the breakup of the Soviet Union. This epidemic, which led to over 157,000 cases of diptheria and 5000 deaths, is now controlled by mass immu￾nization programs. 418 PART IV The Immune System in Health and Disease Paralytic polio 0 cases 1934 1952 Pertussis 1969 Rubella 1921 Diphtheria 1941 Measles Disease 1968 Mumps 1,000,000 100,000 10,000 1,000 Number of reported cases 100 10 0 FIGURE 18-1 Reported annual number of cases of rubella (Ger￾man measles), polio, pertussis (whooping cough), mumps, measles, and diphtheria in the United States in the peak year for which data are available (orange) compared with the number of cases of each dis￾ease in 1999 (green). Currently, vaccines are available for each of these diseases, and vaccination is recommended for all children in the United States. [Data from Centers for Disease Control.] dence of whooping cough, with 7405 cases in 1998. The re￾cent development of an acellular pertussis vaccine that is as effective as the older vaccine, but with none of the side ef￾fects, is expected to reverse this trend. As indicated in Table 18-3, children typically require multiple boosters (repeated inoculations) at appropriately timed intervals to achieve effective immunity. In the first months of life, the reason for this may be persistence of cir￾culating maternal antibodies in the young infant. For exam￾ple, passively acquired maternal antibodies bind to epitopes on the DPT vaccine and block adequate activation of the im￾mune system; therefore, this vaccine must be given several times after the maternal antibody has been cleared from an infant’s circulation in order to achieve adequate immunity. Passively acquired maternal antibody also interferes with the effectiveness of the measles vaccine; for this reason, the MMR vaccine is not given before 12–15 months of age. In Third World countries, however, the measles vaccine is ad￾ministered at 9 months, even though maternal antibodies are still present, because 30%–50% of young children in these countries contract the disease before 15 months of age