IN4 ECONOMIC EVALUATION OF INFLUENZA PANDEMIC MITIGATION STRATEGIES IN THE US USING A STOCHASTIC MICROSIMULATION INFLUENZA MODEL

Objective: To project the potential impact of alternative pandemic influenza mitigation strategies on the number of influenza cases, quality-adjusted life years (QALYs) gained and costs incurred, and to assess their cost-effectiveness from a societal perspsective. Methods: We use a stochastic agent-based model to simulate the impact of pandemic influenza on a typical American community of 1.6 million. We compare 18 strategies to the baseline (no intervention). Our analysis focuses on targeted antiviral prophylaxis (TAP) with oseltamivir (treatment of identified index cases and prophylaxis of exposed people in the key mixing groups of the index case) alone and in combination with school closure. We assume three levels of antiviral stockpile would be available: 25% and 50% of the population, and unlimited. We also consider pre-vaccination of the entire population alone and in combination with school closure. We use the human capital approach to estimate productivity loss due to the intervention, illness due to influenza or its complications, and school closure. Outcomes include number of cases, mortality, QALYs, direct and indirect costs, and incremental cost-effectiveness ratios expressed as costs per QALY gained. Results: In the absence of intervention, the model predicts 50 cases per 100 population. The total economic impact is expected to be $146 per capita (societal perspective). The number of cases can be substantially reduced if a combination of TAP and school closure is chosen. The expected number of cases is smallest (6 per 100 population) and the QALY gain greatest if 60% of close contacts of ascertained index cases are prophylaxed and schools are closed for the duration of the outbreak. However, school closure also incurs substantial costs to society (about $1,900 per capita), driven by extensive work loss for caretakers and teachers. Incremental cost-effectiveness ratios for school closure strategies (alone and in combination with TAP) range from $126,000 to $576,000 per QALY gained. TAP alone effectively prevents 50% of cases of influenza, provides improved health outcomes at lower costs (about $100 per capita), and hence dominates the baseline as well as all strategies involving school closures. Pre-vaccinating 70% of the population with a partially effective vaccine prevents about 50% of cases and is the least costly alternative ($80 per capita). However, safe vaccine may not be available before the onset of a pandemic. Sensitivity analyses shows that mortality is one of the key drivers of QALYs in the model. Assuming a case fatality rate of 2.5%, TAP still dominates strategies involving school closure; however, school closure strategies become more attractive with incremental cost-effectiveness ratios below $30,000 per QALY gained. Vaccination remains an excellent strategy. Results are also sensitive to the cost of school closure, as well as acquisition and distribution cost of antivirals. Conclusions: Targeted antiviral prophylaxis is an effective and cost saving measure for mitigating pandemic influenza in the absence of an effective vaccine. Adding school closure to TAP provides greater benefit in terms of health outcomes and are economically attractive strategies if the mortality rate is high.