Ideally, calculation of the annual costs associated with each of the vaccine candidates would include three major components: (1) the reduction in morbidity costs, (2) the vaccination program costs, and (3) the vaccine development costs. The costs of adverse reactions also should be calculated, if applicable. Such a comprehensive calculation can be attempted where reliable estimates of treatment costs can be made. However, as discussed in Chapter 4, the committee judged that attempting to incorporate the average cost of disease treatment(s) in the developing world into the calculations would be unrealistic. Additionally, the committee assumed that all vaccine candidates would, if developed, be delivered through the WHO-EPI; hence, possible differential utilization or delivery costs would not be a factor in the priority selection of vaccine candidates.

Because of these judgments, the cost comparisons in this analysis are somewhat simplified, including only those expenditures on the candidate vaccines necessary to achieve the potential health benefits. Table 7.3 shows these expenditures: vaccine development costs and vaccine costs for the immunization programs. The annual number of new potential vaccinees is derived as shown in Table 7.1, and Table 5.1 indicates the predicted cost per dose (price) for each vaccine and the number of doses required.

Some clarification of the assumptions underlying vaccine improvement projects may be useful. In these cases, the incremental benefit should be used in comparisons.

For all diseases, the TDBV represents the burden of illness presently occurring with the current vaccine usage. However, in some cases (cholera, yellow fever, Japanese encephalitis, N. meningitidis), the current vaccine use may not be as widespread or, because of vaccination timing or efficacy, as likely to prevent as large a proportion of the disease as would the universal pediatric approach with the improved vaccine assumed in this analysis. Hence, the current disease burden reasonably represents the disease amenable to further control.

For other diseases (H. influenzae type b) the currently available (PRP) vaccine may not be used widely in developing countries either because most disease occurs in age groups (under 2 years) for which the vaccine is ineffective or because the vaccine is relatively new. Hepatitis B vaccine is also not yet widely used in developing countries, probably because it is relatively new and expensive. For these diseases, the present total disease burden is a reasonable starting point for calculations.

Developing an improved vaccine for Streptococcus pneumoniae represents a situation where the assumptions may greatly affect the potential health benefit calculations. The current vaccine is not widely used in the developing world, probably because it is immunogenic