approximately 98.65% by 2025. In the 2035 scenarios, about 98.15% of the total potential gains are appropriated. As the 2025 scenarios eliminate malaria faster, they benefit from a more productive labor force earlier on and also from the allocation of expenditure previously used for malaria to more productive uses such as investments in education and health. The simulations with 2035 as target year for malaria elimination provide the interesting finding of faster gains in GDP resulting from the 2035-IRSFocus policy. As IRS does not require the installation of a capital component, expenditures become effective without major instal- lation delays. Faster malaria improvements enable the economic benefits (more productive labor force and other investments) to materialize earlier. These results proved to be fairly stable and insensitive to changes in the cost-effectiveness assumptions underlying ITN and IRS. A first sensitivity simulation analyzed the impact of variations in the cost-effectiveness of ITN, IRS and EM in a range of 620% of the assumptions used for the previous simulations and reported in Table S1. The simulation used the total malaria prevention expenditure in the 2025-CurrentMix policy. Sensitivity analysis showed that under the most cost-effective assumptions, malaria could be eliminated about four years earlier. Decreases in cost- effectiveness, however, delay malaria elimination up to nine years. This asymmetry around the year 2025 is caused by the adaptation delay of five years during which the absorption capacity for the interventions is gradually implemented and which prevents much faster elimination even under very high cost-effectiveness of IVM interventions. A second round of sensitivity simulations decreased the cost- effectiveness of ITN by 20%, thus taking into account new evidence on reduced ITN effectiveness [40]. At the same time, it increased the cost-effectiveness of IRS by 20% to make ITN even less competitive. With these assumptions, we ran the 2025-policies again. Even under these modified assumptions, the policies maintained their order in terms of overall cost-effectiveness, i.e., the ITN focus mix followed by EM focus, current mix and eventually IRS mix. This must be due to the fact that all combinations of IVM interventions have a considerable ITN component (33 to 66%, see Table 1). The results presented in Figure S7 thus prove to be reasonably stable over a wide range of cost-effectiveness assumptions. Summary of results in light of the research questions At the beginning of this paper we addressed one central research question and four additional questions necessary for putting the central question about the costs and benefits of a continued use of DDT for IRS versus its rapid phase out into perspective. With the results from the simulations with the Malaria Management Model (MMM) we can summarize the answers to these questions as below. Analysis of the baseline scenario (a projection under the current policy framework) indicated an overall improvement in malaria control – although not a very rapid one – with a reduction of malaria cases to about 200 million in 2050. Such results are not to be intended as point-predictions, but rather as the likely tendency if no major shift in policy regime were to take place. Central question: What are the costs and benefits associated with the continued use of DDT for IRS in sub Saharan Africa versus its rapid phase out? The direct economic costs of non-DDT insecticides are approximately 50% higher than those of DDT and the total direct costs for eliminating malaria by 2035 with the current combination of IVM interventions and a rapid phase out of DDT for IRS are about 12% higher than the total costs of the same combination of DDT versus Non-DDT Malaria Control interventions with a continued use of DDT for IRS. A gradual reduction in the price of non-DDT IRS products would further reduce this cost difference. A rapid phase out of DDT, however, creates a series of benefits as well as avoided risks that have the potential of exceeding the additional costs. Phasing out of DDT would avoid the risk of losing some of the agricultural exports outside the SSA region. A loss of exports in the range between 1 and 5% is in the same range as the costs of substituting DDT. Other benefits include health and environmental effects that are difficult to measure. Additional questions: What is the amount of resources necessary to gradually scale up the current or alternative combinations of vector control interventions for achieving malaria elimination in 2025 or in 2035, respectively? How does this amount compare to the gain in GDP that could be achieved through malaria elimination? For all intervention mixes the necessary additional malaria expenditure as a share of total GDP for the time period between now and either 2025 or 2035 (depending on the scenario) needs to be in the range of 0.17 and 0.24 percent to enable elimination. The total average annual costs are around 1.2 Billion US $ (real terms, base 2000), assuming a 3% discount rate. In our policy-scenario tests we found a fairly stable rank order of intervention mixes in terms of their ratio between additional value added by malaria elimination and the costs for achieving this. The stability of this order to variations in cost-effectiveness assumptions is encouraging for an aggregated model such as MMM that requires simplification of the represented processes. All of the tested policy-scenario combinations showed that the average yearly expenditures for malaria prevention were much lower than the possible yearly gain in GDP from eliminating malaria (economic costs of malaria calculated in the hypothetical no malaria scenario). Scaling up funding for malaria control interventions thus seems to be more than viable even from a narrow, purely economic perspective. In terms of the average yearly expenditures, a mix favoring the use of ITN clearly exceeded all other intervention mixes, assuming that the expected improvements in education levels in the future will empower beneficiaries to use bed nets more appropriately than today and thus support the leading role of ITN among IVM interventions. Intervention mixes focusing on environmental management also exhibited fairly low average yearly costs. This supports findings that highlight the importance of EM as a supplement to ITN [41], [42]. It is, however, unclear how broadly these interventions are applicable, i.e., how much they can be scaled up from the current situation [4], [43], [44],). Finally, IRS interventions are the most expensive interventions. A relevant issue regarding the effectiveness of IRS is the mounting resistance of mosquitoes to the sprayed chemicals [45]. Combinations of IVM interventions with a high share of IRS are more expensive than other combinations. However, IVM interventions with a high share of IRS create faster gains in GDP. These analyses reveal a trade off between cost minimization and benefit maximization. Discussion The purpose of this paper was to test the Malaria Management Model (MMM) in a pilot application that provides a differentiated assessment of the costs and benefits of the continued use of DDT for IRS versus its rapid phase. The Malaria Management Model is a prototype of a computer based scenario analysis tool that integrates malaria transmission, case management as well as Integrated Vector Management into a socio-economic develop- ment framework for the case of the aggregated sub Saharan African region. The model studies long-term (1970–2050) trends PLoS ONE | www.plosone.org 8 November 2011 | Volume 6 | Issue 11 | e27771