The Economic Implications of Influenza Vaccination for Adults with Asthma Justin G. Trogdon, PhD, Tursynbek A. Nurmagambetov, PhD, Hope F. Thompson, BA Background: Influenza vaccination is recommended for adults with asthma. Purpose: This study estimates the effect of influenza vaccination on utilization of medical services and expenditures for acute and chronic respiratory conditions (ACRC) among adults with asthma. Methods: The sample was adults aged 18 years self-reporting asthma in the 2003 through 2006 Medical Expenditure Panel Survey (MEPS), covering four complete influenza seasons. The depen- dent variables were indicators for any ACRC claims within service category and ACRC expenditures. The main independent variable was an indicator of influenza vaccination. To control for selection bias in the observational data, a nonlinear instrumental variables approach was used. The instru- ments were indicators for influenza in the fırst year of MEPS and vaccination in the year prior to MEPS. Data were analyzed in 2009. Results: Adults with asthma vaccinated for influenza were 4.4 percentage points less likely to have an inpatient stay due to ACRC (95% CI =-10.8, -1.0). Influenza vaccination was associated with a $492 decrease (95% CI =-$1591, -$56) in annual ACRC nonprescription expenditures, a $224 increase (95% CI = $70, $360) in annual ACRC prescription expenditures, and a nonsignifıcant $216 decrease (95% CI =-$854, $248) in overall annual ACRC expenditures. Conclusions: Although there was no evidence that vaccination reduced overall ACRC expendi- tures, the study suggests that efforts to increase the percentage of adults with asthma who are vaccinated may bring substantial benefıts in terms of reducing the prevalence and costs of hospital- ization although raising prescription medication costs, possibly through improvement in compliance. (Am J Prev Med 2010;39(5):403– 410) © 2010 American Journal of Preventive Medicine Introduction S easonal influenza imposes a major burden on pop- ulation health and the healthcare system. On aver- age, 36,000 deaths and 226,000 hospitalizations were attributable to influenza each year between 1979 and 2001. 1 The fıgures have escalated as the population has aged and developed more medical conditions, putting them at higher risk for influenza complications. 1 Among this high-risk population are people with asthma, 1 for whom influenza complications can trigger asthma at- tacks. For 2008, the CDC 2 reports that 7.3% of non- institutionalized adults currently have asthma. Evidence 3 suggests that the injected influenza vaccine is unlikely to cause short-term exacerbations of asthma and is safe. However, evidence is mixed regarding the effect of vaccination on influenza-related asthma compli- cations. 3 Some studies show signifıcant reductions in asthma complications following influenza vaccination, 4 whereas others 5,6 do not. Economic evaluations of the impact of influenza vac- cination among adults with asthma are rare. The majority of cost-effectiveness studies 7–10 for influenza vaccination among adults have focused on those aged 65 years and fınd that influenza vaccination is cost effective for the elderly. In one study 11 among patients with chronic re- spiratory conditions, vaccination was found to be cost effective among adults aged 65 years but not among those aged 18 – 64 years. Other studies 12–18 have found that vaccination is associated with lower Medicare expen- ditures among Medicare recipients. The present study used data from the Medical Expen- diture Panel Survey (MEPS) to estimate the effect of in- fluenza vaccination on acute and chronic respiratory con- From the Public Health Economics Program (Trogdon, Thompson), RTI International, Research Triangle Park, North Carolina; Air Pollution and Respiratory Health Branch, Division of Environmental Hazards and Health Effects (Nurmagambetov), National Center for Environmental Health, CDC, Atlanta, Georgia Address correspondence to: Justin G. Trogdon, PhD, 3040 Cornwallis Road, P.O. Box 12194, Research Triangle Park NC 27709-2194. E-mail: jtrogdon@rti.org. 0749-3797/$17.00 doi: 10.1016/j.amepre.2010.07.012 © 2010 American Journal of Preventive Medicine. All rights reserved. Am J Prev Med 2010;39(5)403– 410 403