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rate of less than 100% will reduce the health benefits and savings in the cost of care that can be expected. A lower utilization rate will also have the effect of reducing the costs associated with vaccinating the target population.

With regard to efficacy, it was assumed that preventive vaccines would achieve an efficacy level of 75%. The efficacy of therapeutic vaccines was assumed to be 40%. This lower estimate reflected the committee’s belief that therapeutic vaccines would be expected to achieve a lower threshold of efficacy than for preventive vaccines for both licensure approval by the FDA and for acceptance by patients and medical care providers. In fact, many therapeutic drugs are approved for licensure or for new indications with an efficacy of 40% or lower.

Each candidate vaccine was also assigned a utilization rate of 10, 30, 50, 60, or 90% (see Table 4–1). The committee’s utilization rate assignments were guided by an examination of the coverage rates achieved for existing vaccines, which were assumed to suggest rates that could be anticipated for new vaccines. Also considered were specific factors that might influence the rate at which a particular vaccine would be used. For example, a 50% utilization rate by an adolescent target population for a vaccine for a sexually transmitted disease (STD) reflects the committee’s assessment of the difficulty in reaching this population and possible reluctance of parents to acknowledge a child’s risk and therefore the potential benefit of a vaccine. For vaccines targeted to pregnant women, two alternatives were considered plausible: the utilization rate would stabilize at 10% due, in part, to persistent concerns about potential adverse effects on the fetus, or the utilization rate would reach 90% because use of the vaccine becomes an accepted element of good prenatal care.

In the past, more extensive use of some vaccines has been hindered by an inadequate supply. For this analysis, however, it was assumed that adequate supplies would be available to meet the demand for all vaccines.

Cost-Effectiveness Ratios

The final stage/step of the analysis is the calculation of the cost-effectiveness ratio for each candidate vaccine, the basis for comparisons among the vaccines. Three sets of cost-effectiveness ratios were calculated. The first ratio examines the potential impact of the vaccine on morbidity and costs under the assumption that the vaccines are available immediately without any additional cost or time for development and that they are fully efficacious and are used by the entire target population. This comparison focuses attention on what might be considered an ideal vaccine benefit. The second cost-effectiveness ratio factors in the adjustments for incomplete efficacy and use, which tend to increase the cost of achieving the anticipated health benefit. The final ratio shows the impact of the time and money needed to develop these vaccines. Some vaccines that promise substantial benefit require a longer and more expensive period of development, whereas others that offer smaller benefits are ex-



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