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APPENDIX 23
Shigella

DISEASE BURDEN

Epidemiology

For the purposes of the calculations in this report, the committee estimated that there are approximately 30,000 new cases of shigella disease each year in the United States. It is assumed that the highest incidence is in children between the ages of 1 and 4 years of age. Children under one year of age and between 5 and 14 years of age also contribute heavily to the number of cases. It is assumed that there are no deaths associated with shigella infection in the United States. It was assumed that 25% of cases are in travelers from the United States to other countries.

Disease Scenarios

For the purposes of the calculation in this report, the committee assumed that shigella manifests as acute diarrhea lasting 6 days and associated with a health utility index of .51.

COST INCURRED BY DISEASE

For the purposes of the calculations in this report, it was assumed that 25% of people with shigella incur costs associated only with over-the-counter treatment, such as oral rehydration or anti-diarrheals. It was assumed that 75% of



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Vaccines for the 21st Century: A Tool for Decisionmaking APPENDIX 23 Shigella DISEASE BURDEN Epidemiology For the purposes of the calculations in this report, the committee estimated that there are approximately 30,000 new cases of shigella disease each year in the United States. It is assumed that the highest incidence is in children between the ages of 1 and 4 years of age. Children under one year of age and between 5 and 14 years of age also contribute heavily to the number of cases. It is assumed that there are no deaths associated with shigella infection in the United States. It was assumed that 25% of cases are in travelers from the United States to other countries. Disease Scenarios For the purposes of the calculation in this report, the committee assumed that shigella manifests as acute diarrhea lasting 6 days and associated with a health utility index of .51. COST INCURRED BY DISEASE For the purposes of the calculations in this report, it was assumed that 25% of people with shigella incur costs associated only with over-the-counter treatment, such as oral rehydration or anti-diarrheals. It was assumed that 75% of

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Vaccines for the 21st Century: A Tool for Decisionmaking people with shigella infection seek the care of a physician and receive medication. See Table A23–1. VACCINE DEVELOPMENT The committee assumed that it will take 7 years until licensure of a shigella vaccine and that $240 million needs to be invested. It was assumed that research into the development of a shigella vaccine would lead to increased knowledge of mucosal immunity, which would benefit research and development of many vaccines in the future. Table 4–1 summarizes vaccine development assumptions for all vaccines considered in this report. VACCINE PROGRAM CONSIDERATIONS Target Population For the purposes of the calculations in this report, two scenarios are discussed: a target population of travelers only and a target population of travelers and infants. It is assumed that 90% of infants and 30% of travelers will accept the vaccine. Vaccine Schedule, Efficacy, and Costs For the purposes of the calculations in this report, it was estimated that this vaccine would cost $50 per dose and that administration costs would be $10 per dose. Default assumptions of a 3-dose series and 75% effectiveness were accepted. Table 4–1 summarizes vaccine program assumptions for all vaccines considered in this report. RESULTS If a vaccine program for Shigella were implemented today and the vaccine were 100% efficacious and utilized by 100% of the target population, the annualized present value of the QALYs gained would be 160. Using committee assumptions of less-than-ideal efficacy and utilization and including time and monetary costs until a vaccine program is implemented, the annualized present value of the QALYs gained would be 57. If a vaccine program for Shigella were implemented today and the vaccine was 100% efficacious and utilized by 100% of the target population, the annualized present value of the health care costs saved would be $1.7 million.

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Vaccines for the 21st Century: A Tool for Decisionmaking Table A23–1 Health Care Costs Associated with Shigella Infection   % of Cases Cost per Unit Units per Case Form of Treatment Acute diarrhea 25% $10 2.0 oral rehydration therapy   75% $50 1.0 physician a 75% $50 1.0 medication b Using committee assumptions of less-than-ideal efficacy and utilization and including time and monetary costs until a vaccine program is implemented, the annualized present value of the health care costs saved would be $620,000. If a vaccine program for Shigella were implemented today and the vaccine was 100% efficacious and utilized by 100% of the target population, the annualized present value of the program cost would be $1.2 billion. Using committee assumptions of less-than-ideal efficacy and utilization and including time and monetary costs until a vaccine program is implemented, the annualized present value of the program cost would be $550 million. Using committee assumptions of time and costs until licensure, the fixed cost of vaccine development has been amortized and is $7.2 million for a Shigella vaccine. If a vaccine program were implemented today and the vaccine was 100% efficacious and utilized by 100% of the target population, the annualized present value of the cost per QALY gained is $7 million. Using committee assumptions of less-than-ideal utilization and including time and monetary costs until a vaccine program is implemented, the annualized present value of the cost per QALY gained is $9 million. If the vaccine were utilized by 90% of travelers (and no infants) the annualized present value of the cost per QALY gained is $11 million. See Chapters 4 and 5 for details on the methods and assumptions used by the committee for the results reported. READING LIST Ashkenazi S, Cleary TG. Shigella Infections. In: Textbook of Pediatric Infectious Diseases. RD Feigin and JD Cherry eds. Philadelphia, PA: WB Saunder Company, 1992, pp. 637–646. CDC. Summary of Notifiable Diseases, United States 1994. Morbidity and Mortality Weekly Report 1994; 43:1–80. DuPont HL. Shigella Species (Bacillary Dysentery). In: Principles and Practice of Infectious Diseases. GL Mandell, JE Bennett, Dolin R eds. New York, NY: Churchill Livingstone, 1995, pp. 2033–2039.

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