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Calculate Time Intervals for Discounting Future Health Benefits

As noted above, the timing of the health benefits expected from the use of the potential new vaccines included in the committee’s analysis will vary depending on the intervals between the typical age at immunization and the age at onset of an illness or the age at death. The intervals calculated for the analysis are the following: To, the time from vaccination to the average age at onset of illness, and Td, the difference between the average age at onset of illness and average age at the time of illness-related death. Td is of interest for those acute conditions for which the age at death from a condition differs markedly from the overall age of patients with that condition. The time interval related to premature death following a period of chronic illness is accounted for separately.

The distribution of cases and deaths by age was used to estimate the average age at the time of onset of the condition and the average age at the time of death. Specifically, the midpoint of each age group was weighted by the proportion of cases or deaths occurring in that age group:

A=∑(agPg), (6)

where A is the average age of onset (Ao) or death (Ad), a is the midpoint of age group g, and P is the proportion of cases or deaths in age group g.

Age at vaccination, AV, was determined by the vaccination strategy and the target population specified by the committee. Most cases fall into one of the following categories:

Target Population

Age at Vaccination

Infants 6 months

6 months

Adolescents

12 years

Pregnant women

Average age of mothers at first births, minus 2 months (24.7 years)

New cases (therapeutic vaccines)

Age at diagnosis (assumed to equal average age at onset)

See the Appendixes for detailed information on the age at vaccination used for each case.

Thus, the interval from vaccination to onset of illness is calculated as To=Ao−Av, and the difference between age at onset of illness and illness-related death is calculated as Td=Ad−Ao.

Calculate Condition-Related Life Expectancies

The discounted quality-adjusted life expectancies for selected ages were used to calculate the life expectancy in the population at the average age at onset



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