other medical interventions. This makes it even more important that their risk-benefit balance be as favorable as possible.

Second, one must consider very carefully the appropriate target group that should receive the vaccine. For some vaccines, the target group is the entire population. Often, that is because of the phenomenon of “herd immunity”; that is, for diseases that can be transmitted from person to person (e.g., poliomyelitis), it benefits the entire population to have others protected from the disease, as it reduces the risk to the population as well as to the individual. For other vaccines (e.g., tetanus toxoid), the illness cannot be passed from person to person, but the vaccine is nevertheless recommended for use by everyone since everyone is at sufficiently high risk of the disease. For still other vaccines, there are clearly identifiable target groups at higher risk; for example, typhoid vaccine is recommended for use by travelers to developing countries.

In the case of a vaccine against anthrax, the situation is even more complex. The illness cannot be transmitted from person to person. There-fore, there is no possibility of herd immunity, nor is there a reason to vaccinate the entire population. Thus, the vaccine should be targeted to those at higher risk of disease. In light of recent events, however, that target population has become very fluid, whereas formerly it was definable. Historically, the licensed vaccine was recommended only for those at risk for occupational exposure to anthrax bacteria or spores. However, in recent years the risk of biological warfare led to a judgment that military personnel were at occupational risk of exposure and should receive the anthrax vaccine. Recent bioterrorist use of anthrax spores in the U.S. mail system has indicated that some civilian populations might even be considered at sufficient risk to warrant their use of an anthrax vaccine, if one were available, sufficiently safe, and sufficiently effective.

As noted earlier, this report does not address the military policy to vaccinate all service members, nor does it consider which other populations should be considered for vaccination. These questions were not part of the charge to the committee, nor is biological warfare or bioterrorist risk assessment part of its expertise. Rather, the report focuses on the efficacy and safety of the current licensed vaccine and provides information for those who must establish vaccination policy.

ORGANIZATION OF THE REPORT

The varied components of the committee’s statement of task (see Appendix A) fall into broad categories of efficacy, safety, manufacturing, and future needs. This report is organized into these categories as well. Chapter 2 provides background material about the disease known as anthrax, the licensed anthrax vaccine, and the data available for evaluation of its safety



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