staff resource constraints), and the prospects for their development are discussed briefly in the supplement to this volume (see Appendix I). This supplement also includes information on pathogens that cause major global disease problems but that were considered unsuitable for accelerated vaccine development at this time.
One or more vaccine candidates for accelerated development have been identified for each disease. Vaccine descriptions usually are based on current research in specific areas. in some cases, however, the number of vaccine possibilities led the committee to base predictions on a combination of research findings and general knowledge about probable requirements for licensure.
To identify an appropriate vaccine target population, the committee considered the age distribution of the disease consequences (particularly of those conditions considered most desirable to avoid); the relative risk of illness in various geographic population groups; and accessibility to the health care system. For reasons described in the next chapter, the committee assumed that most of the vaccine candidates would be delivered through the World Health Organization Expanded Program on Immunization (WHO-EPI). The effects of this assumption on determinations of vaccine efficacy are outlined below.
Predictions on vaccine development are an attempt to foresee events from 1985 until the time at which vaccine licensure might occur. Predictions are based solely on technical feasibility and not on judgments about the desirability of particular courses of action; no distinction has been made between public and private sector developmental resources.
The likelihood of bringing a specific vaccine to licensure within the time allotted, and with the predicted efficacy and other characteristics, is described as the probability of successful development. This probability is based on the state of current research, the complexity of the problem (e.g., the number of known serologic types), and characteristics of the natural immune response. The committee assumed that vaccine candidates would have to comply with safety and efficacy standards similar to those required by U.S. licensing regulations and the WHO.