ArticlesEradication versus control for poliomyelitis: an economic analysis
Introduction
Economic assessments have prospectively supported the case for poliomyelitis eradication worldwide.1, 2, 3 While preventing hundreds of thousands of cases of paralytic poliomyelitis and premature deaths, the US domestic poliomyelitis vaccination programme also yielded net economic benefits that exceeded US$180 000 million, even without considering the large, intangible benefits associated with avoided fear and suffering.4 These US net benefits greatly exceed the cumulative global investment of more than $4000 million (with much more contributed at the national level) over nearly 20 years for the Global Polio Eradication Initiative (GPEI) by external donors.5 We anticipate that retrospective economic analysis of the GPEI will also show substantial net benefits, if eradication is completed.
In addition to these specific analyses for poliomyelitis, numerous other analyses address the questions and issues related to eradication versus control.6, 7, 8, 9, 10, 11, 12, 13 Notably, Barrett6 emphasised that a disease could be controlled and eliminated locally, but that eradication requires elimination everywhere at the same time, which requires cooperation. Building on that work, Barrett7 specifically explores the investment in eradication and finds that “maintaining a very high level of control can never be optimal, given the technical feasibility of eradication.” This insight is particularly important because it runs counter to the recent suggestion that control should be maintained such that the “annual global number of cases is less than 500” (ie, a policy of high control in perpetuity).14 Barrett and Hoel8 explicitly explore the dynamics of poliomyelitis eradication and provide estimates of thresholds for the welfare cost of paralytic poliomyelitis that must be exceeded to justify eradication (shown separately for rich and poor countries). Geoffard and Philipson9 showed that private markets might have difficulty achieving eradication when the demand for vaccines depends on the prevalence of disease (ie, the demand for vaccine vanishes when prevalence is low enough), and they explore the incentives of various stakeholders. They also show that, for public health expenditures, if the prevalence inversely affects demand for vaccination (ie, perceived benefit of vaccination drops as prevalence decreases) then this leads to a failure to eradicate.
The GPEI succeeded in reducing yearly cases of paralysis from wild polioviruses from an estimated 350 000 cases in 1988 to about 2000 cases in 2006.15 Nonetheless, the goal of worldwide poliomyelitis eradication now faces substantial challenges that include: curtailing transmission of wild polioviruses in the remaining endemic countries; managing the risks of vaccine-derived polioviruses (viruses derived from live oral poliovirus vaccine that have mutated towards neurovirulent forms similar to wild polioviruses); containing live polioviruses in laboratories and vaccine production facilities; and addressing concerns about the risks of reintroductions into countries previously free of wild poliovirus transmission.16, 17, 18, 19, 20, 21, 22, 23, 24, 25
The emergence of circulating vaccine-derived polioviruses in areas of low vaccine coverage20, 26 provides strong motivation for either maintaining high coverage or completely stopping vaccination with oral poliovirus vaccine in the future.24, 27, 28 However, the most important challenge is to justify the continued use of resources (both financial and human) to complete eradication in the next few years. Concerns about whether poliomyelitis eradication is realistic and that “international assistance for polio could have negative effects on other public health efforts” has led to the suggestion that “the time has come for the global strategy for polio to be shifted from ‘eradication’ to ‘effective control.’”14 This recommendation represents a radical shift in policy not supported by estimates of the financial or health implications, and we believe that policymakers should consider any policy change in the context of information about the future risks, costs, and benefits of the alternative options.
Wild polioviruses could theoretically be eliminated in all parts of the world.29 In practice, the GPEI has successfully used existing vaccines to eradicate type 2 wild polioviruses worldwide and eliminate type 1 and 3 in all but four countries, in which transmission of these two serotypes has never been disrupted. In these remaining endemic areas the challenges to elimination differ. Vaccination campaigns in India continue to miss a small percentage of young children in a large and high-density population rapidly generating susceptible people, and sub-optimum immune response to the oral vaccine further compounds the challenge.30, 31, 32 In Nigeria, operational and political issues continue to pose problems, not unlike the challenges faced by that country during the Smallpox Eradication Programme.33 In Afghanistan and Pakistan the challenges relate to security issues associated with current conflicts. Nonetheless, the GPEI overcame similar issues in the past, and accepting these barriers as being insurmountable at this advanced stage should be an unpopular political choice. We emphasise that our analysis focuses on the trade-offs of control versus eradication, assuming that eradication is achievable provided that we are willing to commit the necessary resources, and not on the feasibility of eradication.
In this paper, we develop a dynamic model to show the importance of maintaining and increasing the intensity of immunisation in currently endemic areas to complete eradication. We extend the model to indicate how policies based on perception about high short-term costs or cost-effectiveness ratios without consideration of long-term benefits can undermine any eradication effort and lead to suboptimum policy decisions. Finally, we assess the economic implications and disease burden of a change in policy from eradication to control, and make the case that physicians and global leaders should carefully consider the long-term costs of failing to fully commit to poliomyelitis eradication now.
Section snippets
Methods
We previously developed a model to assess the risks, costs, and benefits of global policies for managing poliomyelitis after eradication24, 34, 35, 36, 37 that stratified the world according to 2002 World Bank income levels.38 This model defined eradication as interruption of wild poliovirus transmission globally. It also included the risks and costs of post-eradication outbreaks from different sources (including vaccine-derived viruses), and recognised the need for high-quality surveillance to
Results
Based on modelling the recent experience in northern India, we show the effects of changing the intensity of immunisation (u) with respect to paralytic incidence. Figure 1 shows that u must be increased to achieve eradication and that the relative amount of increase determines the time until eradication. Even small reductions of u from the immunisation intensity required for eventual eradication û could lead to rapid accumulation of susceptible people and result in many paralytic cases (figure 2
Discussion
Our analysis of low-income countries suggests that eradication is always a better option than control, and that we should be willing to pay thousands of millions of dollars more to achieve this goal. Although we intentionally focused most of our analysis on the low-income countries because they will incur most of the burden of cases if eradication fails, all nations will continue to incur financial costs, implying that the true global willingness to pay is even higher. By contrast, for any
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