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Preattack Vaccination Against Anthrax May Be Cost-effective in Certain Populations

Preattack Vaccination Against Anthrax May Be Cost-effective in Certain Populations Schmitt et al1 report that preexposure anthrax vaccination of US Postal Service (USPS) employees is more costly and results in more anthrax infections and deaths than postattack intervention. We believe that these conclusions are incorrect owing to a flawed study design and several questionable parameter estimates. The most important flaw is the assumption that unvaccinated workers would be denied antibiotics after an attack, especially when 50% adherence to preattack vaccination is presumed. If instead these workers were modeled to receive antibiotics, quality-adjusted life years (QALYs) gained preventing anthrax cases would exceed QALYs lost to vaccine adverse events. Based on the presented incidence, duration and quality-of-life effects of vaccine adverse effects, 0.0000148 QALYs are lost per vaccination series. With a 50% adherence assumption, 2.6 QALYs would be lost because of adverse events. If one assumes that preexposure vaccination is 92.5% effective and considering the data in Table 3 of the article by Schmitt et al,1 a strategy providing antibiotics to exposed but unvaccinated workers would reduce anthrax cases and deaths by 39% (2.4 and 0.7, respectively), providing a gain in QALYs far outweighing QALYs lost to vaccine adverse events. These improved health outcomes can only be assigned to the addition of preattack vaccination to a postattack intervention using antibiotics. Adding postexposure vaccination for these workers would reduce cases and deaths and further improve QALYs gained. The benefits of preattack vaccination beyond 10 years are also not considered. For new workers vaccinated near the end of the 10-year model, vaccination costs are fully captured, while only a few months of vaccine protection are assumed. The authors propose that even if vaccination served to deter an attack on a USPS facility, preattack vaccination would not be cost-effective. Since the cost of preattack vaccination is placed at $105.6 million and the US government spent a greater sum in anthrax remediation efforts at Brentwood (Washington, DC) and Trenton (New Jersey)2 alone, it seems impossible that preattack vaccination would not be cost-effective. We note that Schmitt et al1 assumed a vaccine efficacy of 92.5%. In fact, 100% efficacy was seen in an observational study conducted by the Centers for Disease Control and Prevention of industrial mill workers during 1962 to 1974.3 In this study, no cases of anthrax occurred among workers who received at least 3 vaccinations. Schmitt et al1 assume the cost of giving subcutaneous injections to healthy adults is $20.35, while the mean administration cost assumed in recent studies of workplace influenza vaccination is $8.85 per dose.4-8 The cost-effective use of preventive medical interventions requires targeting individuals at sufficiently high risk. Schmitt et al1 did not consider that certain USPS employees are at greater risk owing to job duties or geographic location. Working near high-speed sorters that could aerosolize anthrax spores is identified as a risk factor by the Occupational Safety and Health Administration.9 Finally, the study did not consider an attack more devastating than that experienced in 2001. Should a much higher rate of infection be modeled because of the very likely possibility of an attack using weapons-grade and/or antibiotic-resistant spores? Future examinations of this subject should recognize that preattack and postattack interventions are complimentary and that individual risk may vary. Such a study will likely find that the best health outcomes will come from preexposure vaccination combined with postexposure vaccination plus antibiotics for previously unimmunized individuals. Correspondence: Dr Hopkins, 300 Professional Dr, Gaithersburg, MD 20879 (hopkinsR@ebsi.com). Financial Disclosure: Drs Hopkins, Waytes, and Zink are employed by Emergent BioSolutions (Rockville, Maryland), the manufacturer of the licensed anthrax vaccine Biothrax. References 1. Schmitt BDobrez DParada JP et al. Responding to a small-scale bioterrorist anthrax attack: cost-effectiveness analysis comparing preattack vaccination with postattack antibiotic treatment and vaccination. Arch Intern Med 2007;167 (7) 655- 662PubMedGoogle ScholarCrossref 2. Wein LMLiu YLeighton TJ HEPA/vaccine plan for indoor anthrax remediation. Emerg Infect Dis 2005;11 (1) 69- 76PubMedGoogle ScholarCrossref 3. Food and Drug Administration, Biological products; bacterial vaccines and toxoids: implementation of efficacy review. Fed Regist 1985;50 (240) 51002- 51117Google Scholar 4. Rothberg MBRose DN Vaccination versus treatment of influenza in working adults: a cost-effectiveness analysis. Am J Med 2005;118 (1) 68- 77PubMedGoogle ScholarCrossref 5. Bridges CBThompson WWMeltzer AI et al. Effectiveness and cost-benefit of influenza vaccination of healthy working adults. JAMA 2000;284 (13) 1655- 1663PubMedGoogle ScholarCrossref 6. Dille JH A worksite influenza immunization program: impact on lost work days, health care utilization, and health care spending. AAOHN J 1999;47 (7) 301- 309PubMedGoogle Scholar 7. Nichol KL Cost-benefit analysis of a strategy to vaccinate healthy working adults against influenza. Arch Intern Med 2001;161 (5) 749- 759PubMedGoogle ScholarCrossref 8. Campbell DSRumley MH Cost-effectiveness of the influenza vaccine in a healthy, working-age population. J Occup Environ Med 1997;39 (5) 408- 414PubMedGoogle ScholarCrossref 9. Occupational Safety and Health Administration, Yellow zone: workplaces where contamination with anthrax spores is possible. http://www.osha.gov/dep/anthrax/matrix/anthraxmatrixyellow.html. Accessed April 24, 2007 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Internal Medicine American Medical Association

Preattack Vaccination Against Anthrax May Be Cost-effective in Certain Populations

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Publisher
American Medical Association
Copyright
Copyright © 2008 American Medical Association. All Rights Reserved.
ISSN
0003-9926
eISSN
1538-3679
DOI
10.1001/archinternmed.2007.27
Publisher site
See Article on Publisher Site

Abstract

Schmitt et al1 report that preexposure anthrax vaccination of US Postal Service (USPS) employees is more costly and results in more anthrax infections and deaths than postattack intervention. We believe that these conclusions are incorrect owing to a flawed study design and several questionable parameter estimates. The most important flaw is the assumption that unvaccinated workers would be denied antibiotics after an attack, especially when 50% adherence to preattack vaccination is presumed. If instead these workers were modeled to receive antibiotics, quality-adjusted life years (QALYs) gained preventing anthrax cases would exceed QALYs lost to vaccine adverse events. Based on the presented incidence, duration and quality-of-life effects of vaccine adverse effects, 0.0000148 QALYs are lost per vaccination series. With a 50% adherence assumption, 2.6 QALYs would be lost because of adverse events. If one assumes that preexposure vaccination is 92.5% effective and considering the data in Table 3 of the article by Schmitt et al,1 a strategy providing antibiotics to exposed but unvaccinated workers would reduce anthrax cases and deaths by 39% (2.4 and 0.7, respectively), providing a gain in QALYs far outweighing QALYs lost to vaccine adverse events. These improved health outcomes can only be assigned to the addition of preattack vaccination to a postattack intervention using antibiotics. Adding postexposure vaccination for these workers would reduce cases and deaths and further improve QALYs gained. The benefits of preattack vaccination beyond 10 years are also not considered. For new workers vaccinated near the end of the 10-year model, vaccination costs are fully captured, while only a few months of vaccine protection are assumed. The authors propose that even if vaccination served to deter an attack on a USPS facility, preattack vaccination would not be cost-effective. Since the cost of preattack vaccination is placed at $105.6 million and the US government spent a greater sum in anthrax remediation efforts at Brentwood (Washington, DC) and Trenton (New Jersey)2 alone, it seems impossible that preattack vaccination would not be cost-effective. We note that Schmitt et al1 assumed a vaccine efficacy of 92.5%. In fact, 100% efficacy was seen in an observational study conducted by the Centers for Disease Control and Prevention of industrial mill workers during 1962 to 1974.3 In this study, no cases of anthrax occurred among workers who received at least 3 vaccinations. Schmitt et al1 assume the cost of giving subcutaneous injections to healthy adults is $20.35, while the mean administration cost assumed in recent studies of workplace influenza vaccination is $8.85 per dose.4-8 The cost-effective use of preventive medical interventions requires targeting individuals at sufficiently high risk. Schmitt et al1 did not consider that certain USPS employees are at greater risk owing to job duties or geographic location. Working near high-speed sorters that could aerosolize anthrax spores is identified as a risk factor by the Occupational Safety and Health Administration.9 Finally, the study did not consider an attack more devastating than that experienced in 2001. Should a much higher rate of infection be modeled because of the very likely possibility of an attack using weapons-grade and/or antibiotic-resistant spores? Future examinations of this subject should recognize that preattack and postattack interventions are complimentary and that individual risk may vary. Such a study will likely find that the best health outcomes will come from preexposure vaccination combined with postexposure vaccination plus antibiotics for previously unimmunized individuals. Correspondence: Dr Hopkins, 300 Professional Dr, Gaithersburg, MD 20879 (hopkinsR@ebsi.com). Financial Disclosure: Drs Hopkins, Waytes, and Zink are employed by Emergent BioSolutions (Rockville, Maryland), the manufacturer of the licensed anthrax vaccine Biothrax. References 1. Schmitt BDobrez DParada JP et al. Responding to a small-scale bioterrorist anthrax attack: cost-effectiveness analysis comparing preattack vaccination with postattack antibiotic treatment and vaccination. Arch Intern Med 2007;167 (7) 655- 662PubMedGoogle ScholarCrossref 2. Wein LMLiu YLeighton TJ HEPA/vaccine plan for indoor anthrax remediation. Emerg Infect Dis 2005;11 (1) 69- 76PubMedGoogle ScholarCrossref 3. Food and Drug Administration, Biological products; bacterial vaccines and toxoids: implementation of efficacy review. Fed Regist 1985;50 (240) 51002- 51117Google Scholar 4. Rothberg MBRose DN Vaccination versus treatment of influenza in working adults: a cost-effectiveness analysis. Am J Med 2005;118 (1) 68- 77PubMedGoogle ScholarCrossref 5. Bridges CBThompson WWMeltzer AI et al. Effectiveness and cost-benefit of influenza vaccination of healthy working adults. JAMA 2000;284 (13) 1655- 1663PubMedGoogle ScholarCrossref 6. Dille JH A worksite influenza immunization program: impact on lost work days, health care utilization, and health care spending. AAOHN J 1999;47 (7) 301- 309PubMedGoogle Scholar 7. Nichol KL Cost-benefit analysis of a strategy to vaccinate healthy working adults against influenza. Arch Intern Med 2001;161 (5) 749- 759PubMedGoogle ScholarCrossref 8. Campbell DSRumley MH Cost-effectiveness of the influenza vaccine in a healthy, working-age population. J Occup Environ Med 1997;39 (5) 408- 414PubMedGoogle ScholarCrossref 9. Occupational Safety and Health Administration, Yellow zone: workplaces where contamination with anthrax spores is possible. http://www.osha.gov/dep/anthrax/matrix/anthraxmatrixyellow.html. Accessed April 24, 2007

Journal

Archives of Internal MedicineAmerican Medical Association

Published: Jan 14, 2008

Keywords: anthrax disease,cost effectiveness,vaccination

References