Cost-Effectiveness of Vaccination against Invasive Pneumococcal Disease among People 50 through 64 Years of Age: Role of Comorbid
Conditions and Race

Figure. The diagram represents the three states of health in the model used for the decision and cost-effectiveness analysis:
invasive pneumococcal disease, average health, and dead. A person in the general immunocompetent population or high-risk population
in average health for the respective group enters at the left, at the decision node, to become vaccinated or remain unvaccinated.
Each cohort is assumed to make up the entire population and is effectively infinite. Progressing to the right, the vaccinated
and unvaccinated cohorts face different probabilities of incurring invasive pneumococcal disease, contingent on vaccination
status, and death, conditional on disease status. A person who incurs invasive pneumococcal disease has a lower quality of
life during the illness, assumed to last 34 days (National Center for Health Statistics, National Health Interview Survey.
Unpublished data, 1993), and a risk for death from invasive pneumococcal disease but has average health and quality of life
for the person's age group for the rest of that year. The model assumes that a person who survives invasive pneumococcal disease
in 1 year has the same (average) probability of incurring invasive pneumococcal disease in subsequent years. The model incorporates
a 1-year cycle to reflect that the data, including the probability of incurring invasive pneumococcal disease, the probability
of dying, the effectiveness of vaccination, and the discount rate, were based on 1-year periods. After 6 years, the assumed
duration of vaccination protection, both cohorts face the same risks for invasive pneumococcal disease, average health, and
death. The analysis sums and discounts net medical costs and quality-adjusted life-years ( ) to derive the cost-effectiveness
ratio.
Markov decision model.QALYs
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Ann Intern Med
June 17, 2003
vol. 138
no. 12
960-968