The committee notes that a policymaker concerned with decisions about investing in vaccine R&D might consider on an ad hoc basis a candidate vaccine that precipitously emerges in importance for any of several reasons (e.g., sudden shift in disease epidemiology, genetic variations, or new information linking an infectious agent to serious and chronic disease). Obviously, the committee could not second-guess such a situation and include an example.

The committee included three candidate vaccines of primary importance to a geographically restricted target population. These candidate vaccines are directed against Coccidioides immitis, Histoplasma capsulatum, and Borrelia burgdorferi. The analysis of these candidate vaccines illustrates how regionally important candidate vaccines stand in a ranking based on national importance. If one assessed the potential benefit of these vaccines compared to other candidate vaccines for those regions alone, the benefits might be quite large and apparent. The committee’s model could also be used for such an assessment of regional vaccine programs.

The committee made an explicit decision to include in its analysis two candidate vaccines that were very far along in the development process. The committee knew that vaccines for both rotavirus and Borrelia burgdorferi could be licensed before the report was completed. In fact, vaccines for these pathogens were licensed in August 1998 and December 1998, respectively. The committee believed that readers of the report might wish to know how these vaccines compare to others in an analysis such as that performed for this report. In addition, it should be noted that the newly licensed vaccine for Borrelia burgdorferi is currently approved by the Food and Drug Administration for use only in people between 15 and 70 years of age. The analysis in the report is for a vaccine licensed for use in infancy. The rotavirus vaccine recently licensed matches the candidate vaccine analyzed in the report.

Other important reasons considered by the committee for including a candidate vaccine were that the population most at risk for the disease is very vulnerable. The committee ultimately decided not to include in its analysis a candidate vaccine against Pseudomonas aeruginosa. This infection is an important source of morbidity and mortality in persons with cystic fibrosis. It was not, however, felt to be a significant source of disease in otherwise healthy individuals. Other examples of vulnerable populations considered by the committee include organ transplant patients and persons otherwise immunocompromised, such as those with AIDS. Such populations are sometimes quite small, but the potential reductions in health care costs and improvements in health status by preventing infections make development of certain candidate vaccines worth considering.

Finally, vaccine development efforts for some diseases that impose relatively little disease burden can lead to scientific advances that will be influential for vaccine R&D years later for candidate vaccines for other diseases. For example, the committee believed that research into a vaccine against Streptococcus mutans will lead to benefits far beyond those achieved by prevention of dental