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Perspective
Cost-effectiveness of West
Nile Virus Vaccination
Armineh Zohrabian,*
Edward B. Hayes,† and Lyle R. Petersen†
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; and
†Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
Appendix 2. Discounting, Lifetime
Disability Costs, and Costs due to Death
Discounting is an economic notion that even in a world of zero inflation,
a dollar today would be of higher value to a person than a dollar in the
future. The premium placed on benefits today versus the future is reflected
in the rate at which a person is willing to exchange present for future
costs and benefits. This quantitative measure of time preference is called
the discount rate. When the costs or benefits under the study continue
in the future, to make them comparable in terms of the time dimension
economists calculate the present value of these costs or benefits by using
discount rates. Different discount rates have been used in the literature:
conceptually the appropriate discount rate depends on the perspective
of the study and the question it poses. The US Public Health Service Panel
on Cost-effectiveness in Health and Medicine recommends a 3% discount
rate for economic studies in health (1).
The average societal cost due to death from West Nile virus (WNV) disease
was estimated by using productivity loss tables (2)
(we adjusted the costs from 2000 dollars to 2004 dollars) and the age
distribution of 713 WNV nationwide deaths reported to the ArboNET database
of the Centers for Disease Control and Prevention (CDC) since 1999 (CDC
2005, unpub. data). We estimated these costs both at a 5% and a 3% discount
rates and, following the recommendations by the US Public Health Service
Panel on Cost-effectiveness in Health and Medicine (1),
we used the 3% discount rate estimate in our model, which yielded a death
cost of $200,000 in 2004 dollars (at a 5% discount rate the death cost
was $170,000 in 2004 dollars).
As a proxy for lifetime disability costs due to WNV illness, because
of insufficient data, we used the lifetime costs of stroke available from
the literature (3). Although the disability cost
of stroke may underestimate the disability cost due to WNV because the
median age for WNV neuroinvasive patients is lower (64 years of age [4])
than the median age of persons disabled due to stroke (76 years of age
[5]), this will not have significant effect on
the results because the cost-effectiveness ratio was not sensitive to
changes in the cost of disability. The estimate of the cost of disability
due to stroke in 1990 dollars was discounted at a 5% rate. We converted
this estimate to 2004 dollars by using the Consumer Price Index for medical
care (6) and the average hourly earnings of production
workers (7). This estimate was ≈$180,000
in 2004 dollars.
To make the lifetime disability costs and the death costs comparable,
we used the ratio of the 3% discounted death cost ($200,000) and the 5%
discounted death cost ($170,000) as a multiplier for adjusting the disability
cost discounted at a 5% ($180,000) to a disability cost discounted at
3%. The result was $210,000 in 2004 dollars, which we used as an estimate
for a 3% discounted disability cost.
Appendix
2 References
- Corso PS, Haddix AC. Time effects. In: Haddix AC,
Teutsch SM, Corso PS, editors. Prevention effectiveness. 2nd ed. New
York: Oxford University Press; 2003. p. 94–5.
- Grosse SD. Appendix I. Productivity loss tables. In: Haddix AC, Teutsch
SM, Corso PS, editors. Prevention effectiveness. 2nd ed. New York: Oxford
University Press; 2003. p. 255–7.
- Taylor TN, Davis PH, Torner JC, Holmes J, Meyer JW, Jacobson MF. Lifetime
cost of stroke in the United States. Stroke. 1996;27:1459–66.
- O'Leary DR, Marfin AA, Montgomery SP, Kipp AM, Lehman JA, Biggerstaff
BJ, et al. The
epidemic of West Nile virus in the United States, 2002. Vector Borne
Zoonotic Dis. 2004;4:61–70.
- Kalra L, Evans A, Perez I, Melbourn A, Patel A, Knapp M, Donaldson
N. Training
carers of stroke patients: randomised controlled trial. BMJ. 2004;328:1099.
- Bureau of Labor Statistics. US Department of Labor. Consumer price
index—all urban consumers. Medical Care. 2003 [cited 2005 May 20].
Available from http://www.bls.gov/cpi/home.htm
- Bureau of Labor Statistics. US Department of Labor. National employment,
hours and earnings. 2004 [cited 2005 May 20]. Available from http://www.bls.gov/ces/home.htm
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