availability of alternative control strategies or safe and effective therapy

• possible synergistic interaction with other diseases

• the immediate U.S. interest in diseases that may be imported into the United States, that threaten travelers or personnel stationed overseas, or that are existing problems in the United States

The committee sought to develop a flexible system that could be updated as necessary. This required identifying explicitly all assumptions, estimates, and predictions incorporated in each calculation. Numerical values incorporated into the calculations represent the committee’s best efforts to develop the necessary information. It is recognized that scientific opinion differs on some of the judgments and that uncertainty surrounds other factors, for example, probable vaccine efficacy and disease incidence. The final format allows users of the system to perform sensitivity analyses in which an estimate or prediction in a specific area, such as the probability of success, can be varied systematically across its plausible range to examine its impact on the final result. Some sensitivity analyses are discussed in Chapter 9.

Chapter 3 presents an overview of the approach used in this report. It also identifies certain concepts and basic assumptions that are used throughout the study. For example, if a candidate vaccine is omitted from the full analysis, no conclusions should be drawn regarding its position relative to the assessed contenders. The assessment is conducted from an aggregate perspective for the developing world as a whole, and each development project is treated as an independent investment decision. Effects of morbidity and mortality are expressed in nonmonetary terms.

This report does not make a judgment about the number of vaccines that are worthy of development. It also does not attempt to compare the benefits of basic research with those of vaccine development.

The committee defined candidates for accelerated development as those for which success was reasonably foreseeable within the next decade. The criterion for inclusion was whether a reasonable consensus could be identified on the nature of potential vaccine components (protective antigens). A more detailed description of the selection process appears in Appendix A.

The diseases and vaccine candidates chosen for assessment are shown in Table 1.1. Detailed information about individual candidates is presented in Appendixes D-1 through D-19. The committee and its advisers reviewed the prospects for immunizing against a number of major diseases for which accelerated vaccine development was ultimately judged not to be feasible or appropriate at this time. That information will be included in a supplement to this volume (see Appendix I). The supplement also will briefly describe some newer techniques that are likely to be increasingly applied to vaccine