The calculation of health benefits from vaccine use for each condition under study is a multistep process. The steps are listed in Box 5–1 and are described in the sections that follow.

For each condition studied, the committee, with the advice of outside experts, developed morbidity scenarios to describe the characteristic sequences of acute or chronic health states, the duration of each health state, and the proportion of persons with the condition who experience each scenario. The scenarios also capture the premature mortality associated with a condition but which is delayed 1 or more years beyond the onset of the condition. For most of the conditions included in the committee’s analysis, several scenarios were required to depict the associated morbidity.

Some pathogens or conditions affect specific subpopulations in distinctive ways. For example, the consequences of infection with chlamydia, a sexually transmitted disease, are very different in men and women. For those conditions, separate morbidity scenarios were defined for each appropriate subpopulation. The subpopulation analyses were combined in the final stages of the calculation of the cost-effectiveness ratio.

Once the morbidity scenarios were developed, the committee reviewed each health state and assigned a level in each of the seven attributes of HUI Mark II. To better reflect the range of morbidity represented by some health states, the committee estimated the proportion of cases of illness that should be assigned to each level of a specific health utility attribute. The preference score for the attri bute was calculated as a weighted average of the scores for each level. The quality-adjustment weight for the health state was obtained by combining the scores for each attribute according to Equation 4. The calculations were performed using an Excel spreadsheet template.

The quality-adjustment weights for each condition’s morbidity scenarios (described above) were used to measure QALYs without the vaccine intervention. Quality-adjustment weights reflecting the average health status of the