RESEARCH per LYS). At lower values of VE (37%) or at higher val- ues of R0 (1.8), prepandemic vaccination alone was domi- nated by prepandemic vaccination combined with antiviral drug treatment, which offered reasonable value for money (ICER <$3,500/LYS) when compared with antiviral drug treatment alone. When we considered a VE of 20%, the addition of prepandemic vaccination to antiviral treatment alone cost ≈$9,000/LYS. To be cost saving, prepandemic vaccine (strategy 3) and antiviral drug treatment (strategy 2) would have to be priced at <$3.1/dose and <$10.0/course when compared with the minimum pharmaceutical intervention. Variation in most other parameters did not affect the cost-effective- ness of strategies relative to each other. When the CAR was reduced (20% in the absence of any intervention) as a result of the percentage of asymptomatic infections, the ICER of all strategies increased. However, all strategies still had an ICER <$10,000/LYS. When we assumed the pandemic was relatively mild (case-fatality and case-hospitalization rates 5× less than base-case) and occurred 30 years later, all strategies had ICERs >$50,000/LYS. Varying the age distribution of severe clinical cases (case-fatality and case- hospitalization cases) had only a minor impact on the cost- effectiveness. When we varied the discounting rate (to be either 0% or 3% for costs and effects), ICER for all strate- gies decreased with no change to strategy order. Variation in other parameters was explored in probabilistic sensitiv- ity analysis. Probabilistic Sensitivity Analyses Cost-effectiveness acceptability curves (Figure 3) en- able decision makers to estimate the probability that a strat- egy is optimal as a function of their willingness to pay for additional units of effect. At decision makers’ willingness to pay >$24,000/LYS, more than half of simulations found that a prepandemic vaccination program combined with antiviral treatment was cost-effective in Australia (Figure 3, panels A and C). However, when we assumed that half of the time the emergent pandemic strain would have a different subtype than that chosen for the stockpiled vaccine (Figure 3, panels B and D), most simulations (willingness to pay >$12,000/ LYS) found that antiviral drug treatment alone was the op- timal strategy. Discussion Under the assumption of a severe pandemic occur- ring in the near future, the pharmaceutical-based mitiga- tion strategies examined were generally estimated to be cost-effective. For at least some of the plausible range of transmission parameters, strategies involving population prepandemic vaccination were effective in containing an outbreak until the arrival of a matched vaccine. A combina- tion of antiviral drug treatment and prepandemic vaccina- tion offered the best protection for the population. From a societal perspective, prepandemic vaccination was esti- mated to be cost saving when compared with the minimum pharmaceutical intervention. The cost-effectiveness of pandemic inﬂuenza mitigation strategies was quite resilient to major changes in inﬂuential parameters such as the value of R0 and the effectiveness of vaccination and antiviral drugs. This resilience stems from 2 important assumptions: 1) we assumed that the pandemic would be severe (our base-case has similar characteristics to the 1918 pandemic); and 2) we assumed a pandemic would Figure 3. Cost-effectiveness acceptability curves. Panels A and B show the healthcare system perspective; C and D show the societal perspective. In B and D, we assumed that half of the time (Q = 50%) the emergent pandemic strain would be would be of a subtype to which the stockpiled vaccine offered no protection. We did not explore the use of such a vaccine in subsequent pandemics. Costs and life-years discounted at 5% annually. A$, Australian dollars; LYS, life-year saved. 228 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 16, No. 2, February 2010