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constraints. Pathogens for which accelerated vaccine development did not seem appropriate at this time and the reasons for their exclusion are described briefly in the latter portion of Appendix B, which also contains suggestions for marginal candidates that should be included in future applications of the method or kept under regular review (e.g., an improved vaccine for Streptococcus pneumoniae).

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.

Determination of Health Benefits

To compare diseases and vaccines, it was necessary to develop a system that would allow expression of the total morbidity and mortality associated with each disease as a single number.* The system that evolved, described in Chapter 4, consolidates information on the annual numbers of episodes of illness and their durations with additional data on related complications, sequelae, and deaths. It also incorporates value judgments on the undesirability (disutility) of various conditions occurring in different age groups.

Disease Burden Estimates

Whenever possible, disease burden estimates were based on data from the Centers for Disease Control or other knowledgeable sources. For many conditions, however, information needed to estimate disease burdens was not available or was not of the desired quality; in these cases, calculations were based on judgments and assumptions made by committee members and staff with the aid of consultants. Table 1.2 presents an example of the format used to consolidate disease burden information.

Infant Mortality Equivalence Values

An important feature of the system is that it allows the user to change the perspective on disutility to any level desired and to observe the effect of this change on rankings. The undesirability of conditions for morbidity category/age group combinations are expressed as infant mortality equivalence (IME) values, i.e., the number of acute morbidity days or chronic cases considered to be equal in undesirability to the death of an infant. Two perspectives are used as examples throughout this report: one reflects the median of committee member perspectives (elicited by means of a questionnaire [see Appendix Q]) and the other is an age-neutral perspective (Table 1.3). The

*

See Appendix R for information on the computer software used in this analysis.



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