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Prioritizing Influenza Vaccination
To the Editor: The sudden loss of half of the anticipated United States influenza vaccine supply raises the possibility of increased morbidity and mortality among persons in high-risk groups for the 2004-2005 season. Based on the 2002 National Health Interview Survey, the US Centers for Disease Control and Prevention (CDC) estimates that there are 98.2 million high-risk individuals in the United States, including 36 million people older than 65 years.1 To date, 30 million doses of vaccine have been distributed and another 28 million doses are anticipated, enough to vaccinate only 60% of all high-risk patients.2 Publicity surrounding the shortage has created demand even among lower-risk adults, further threatening the supply for those who need it most. Despite the CDC’s recommendation that all priority groups "are considered to be of equal importance,"2 the risk to individual patients within priority groups varies considerably depending on age and comorbid conditions. This study compared allocation of limited vaccine supply using a vaccine lottery strategy vs a targeted vaccination strategy in terms of the potential impact on hospitalizations and deaths resulting from an influenza epidemic.
Methods
A clinical prediction rule developed by Hak et al3 was used to estimate the effects of a targeted strategy. The rule, used to predict hospitalization or death due to pneumonia or influenza, was derived from 16 000 unvaccinated persons older than 65 years and validated in 11 cohorts.3 In that study, the most vulnerable elderly persons faced a risk more than 60 times that of healthy persons aged 65 to 75 years, and vaccination reduced the risk of hospitalization or deaths from pneumonia by approximately 33%, with an efficacy similar across risk groups, consistent with the findings of others.4-5 Assuming a similar efficacy this year, the predicted effect on the entire US elderly population was calculated for 2 different vaccination strategies: random allocation via a lottery, in which vaccinating all patients older than 65 years is considered to be of equal importance, and targeted allocation, in which vaccine is prioritized to those at highest risk (risk score  50). Since it is unlikely that all available vaccine would be distributed only to high-risk persons, it was assumed that with random allocation 50% of patients in each risk group would receive vaccine, with a corresponding 16.5% decrease in hospitalizations and deaths for each risk group. With targeted allocation, all patients with a risk score of 50 or greater would have a 33% decrease in hospitalizations, while the others would have no decrease at all.
Results
The impact of both strategies is shown in the Table. Vaccinating just the group at highest risk, which would require only 2.7 million doses of vaccine, could avoid 47% of all preventable influenza-related hospitalizations and deaths resulting from an epidemic in persons older than 65 years. Targeted vaccination would result in more than 100 000 fewer hospitalizations than random allocation. Assuming that 60% rather than 50% of the high-risk group would get vaccinated with random allocation had only a small effect on the results.
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Table. Predicted Effects of 2 Different Vaccine Allocation Strategies on Hospitalizations and Deaths From Influenza in Elderly Persons During an Epidemic
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Comment
Two limitations of this study should be noted. First, it is based on data and risk distribution from a single prediction-rule study. However, within that study the rulewas validated. Second, there may be barriers to implementing a targeted program. Nevertheless, these results suggest that, while every effort should be made to divert remaining vaccine supplies toward the target groups identified by the CDC, wherever there are insufficient doses for all target-group members, those at highest risk should receive priority. This group includes anyone with a previous hospitalization for pneumonia or influenza, all persons older than 80 years, and patients aged 65 to 80 years with a history of cancer, pulmonary disease, heart disease, dialysis, dementia, or stroke. Encouraging healthy patients younger than 75 years to wait until those at highest risk have had a chance to be vaccinated can help maximize the population outcome this influenza season.
Michael Rothberg, MD, MPH
michael.rothberg{at}bhs.org
Division of General Medicine and Geriatrics
Department of Medicine
Baystate Medical Center
Springfield, Mass
1. US Centers for Disease Control and Prevention. Interim Estimates of Populations Targeted for Influenza Vaccination from 2002 National Health Interview Survey Data and Estimates for 2004 Based on Influenza Vaccine Shortage Priority Groups. Available at: http://www.cdc.gov/flu/professionals/vaccination/pdf/targetpopchart.pdf. Accessed October 26, 2004.
2. US Centers for Disease Control and Prevention. Interim Influenza Vaccination Recommendations—2004-05 Influenza Season. Available at: http://www.cdc.gov/flu/protect/whoshouldget.htm. Accessed October 26, 2004.
3. Hak E, Wei F, Nordin J, Mullooly J, Poblete S, Nichol KL. Development and validation of a clinical prediction rule for hospitalization due to pneumonia or influenza or death during influenza epidemics among community-dwelling elderly persons. J Infect Dis. 2004;189:450-458.
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4. Nichol KL, Nordin J, Mullooly J, Lask R, Fillbrandt K, Iwane M. Influenza vaccination and reduction in hospitalizations for cardiac disease and stroke among the elderly. N Engl J Med. 2003;348:1322-1332.
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5. Nichol KL, Wuorenma J, von Sternberg T. Benefits of influenza vaccination for low-, intermediate-, and high-risk senior citizens. Arch Intern Med. 1998;158:1769-1776.
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Letters Section Editor: Robert M. Golub, MD, Senior Editor.
JAMA. 2004;292:2582-2583.
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