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achieving early benefits was examined by selecting discount rates higher (0.10) and lower (0.02) than in the central analysis. Results from analyses using these discount rates are compared to results from the central analysis in Tables 9.5 and 9.6.

In general, using discount rates of 10 percent or 2 percent would not substantially affect the structure of the ranking, although some vaccines are shifted slightly in position. Notable among these is hepatitis B, which drops from position 9 on health benefits to position 15 if a 10 percent discount rate is adopted. Although the development of this second generation vaccine is relatively advanced, it drops in position when a high discount rate is adopted (i.e., one that favors shorter term realization of benefits) because the delay of vaccination benefits for hepatitis B immunization is long.

Alternative Development Scenario: Probability of Success

The central analysis uses the probability of successful development indicated for each vaccine in Chapter 5. The effect of adopting a more optimistic but not unreasonable view was examined by assuming a 100 percent chance of successful development within a time period for likely time to licensure. Tables 9.7 and 9.8 show the results. Such an assumption would not substantially affect the overall rankings, but some vaccines shift slightly in position. Some vaccines with lower probabilities of success (e.g., malaria at 0.5) rise in the rankings relative to those whose probability of success was already closer to 1.0. The spacing of benefit values is such that, for certain vaccines (e.g., M. leprae) with a lower probability of success, the more optimistic assumption (p=1.0) raises the potential benefit value but does not change the ranking.

The committee performed another sensitivity analysis, by way of example, to show the effects of lowering the probability of successful development for a single, highly ranked, vaccine—S. pneumoniae (Table9.9). The original estimate, shown in Tables 9.1 and 9.2, was 80 percent. Elimination of this vaccine from the top half of the ranking on potential health benefits (Table 9.2) required assuming a probability of success less than 5 percent. Assuming a probability of success less than about 12 percent is required to eliminate it from the top five positions.

Assessing the Effect of Differential Utilization

Table 9.2 shows annualized present values of potential health benefits (APVPHBs) unadjusted for utilization because the committee assumed this factor would not differ among vaccines. If future applications of this or similar systems (e.g., for specific countries) must account for differential utilization, then the appropriate values for the annualized present values of expected health benefits can be obtained simply by multiplying the APVPHBs by the appropriate value for that proportion of the target population expected to receive the vaccine.

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