The Risks, Costs, and Benefits of Possible Future Global Policies for Managing Polioviruses
by Kimberly M. Thompson, Radboud J. Duintjer Tebbens, Mark A. Pallansch, Olen M.Kew, Roland W. Sutter, R. Bruce Aylward, Margaret Watkins, Howard E. Gary, James P. Alexander, Hamid Jafari, and Stephen L. Cochi, American Journal of Public Health 2008;98(7):1322-1330

Answers to frequently asked questions

What are the study’s main findings?
What are the study’s main recommendations?
How does the model work?
Why doesn’t the paper report numerical cost-effectiveness ratios for some policy comparisons?
Background on polio

What are the study’s main findings?

• Estimates from a probabilistic dynamic model that integrates information about the costs, risks, and dynamics of potential outbreaks for a large number of policy decisions suggest that under any future policy we should expect to continue to incur some financial costs and to see at least one outbreak (defined as one or more cases of paralytic polio) during the 20-year time period after eradication of wild polioviruses.
• Based on the expected (mean) outcomes for different policies, the study finds that complete cessation of routine polio vaccination (“no routine”) saves both costs and paralytic polio cases compared to continued routine oral poliovirus vaccine (OPV) vaccination (with or without supplemental immunization activities (SIAs) used to boost population immunity).
• Continued routine vaccination with OPV will lead to continued frequent outbreaks of circulating vaccine-derived poliovirus (cVDPV) and a substantial burden of paralytic polio cases over a 20-year time period, with the greatest burden in low-income countries (particularly if they do not continue SIAs).
• Switching from OPV without SIAs to routine IPV use would save more (expected) lives than simply stopping all routine vaccination, but it would do so at a relatively high cost, such that decision makers would most likely not consider switching to IPV cost-effective. However, in middle-income countries, switching to routine IPV compared to OPV with SIAs emerges as cost and life saving.
• Given that the option of IPV may not appear attractive compared to “no routine” based on cost-effectiveness criteria, new technology to make IPV less expensive will influence national choices about using IPV to further reduce the small expected burden of paralytic polio cases with “no routine.”
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• Countries should synchronize and coordinate the global cessation of routine OPV use.
• The global health community should minimize the impact of likely post-eradication outbreaks by establishing a globally managed vaccine stockpile and mechanisms to rapidly respond to outbreaks.
• Countries considering a switch to IPV after OPV cessation should carefully consider the trade-offs and opportunity costs of IPV vaccination.
• Further research is needed to refine the economic estimates, optimize policy decisions at a more detailed level, and address remaining open questions.
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• Figure 1 in the paper shows the components of the model. The model performs 10,000 stochastic iterations to capture the uncertainty and variability in the cost and risk inputs. We characterize the consequences of outbreaks using a dynamic sub-model, based on randomly drawn population sizes and conditions that depend on policy choices. The model collects information for each outbreak and aggregates costs and cases for every iteration, yielding distributions of total costs and total cases for each policy decision. To provide a visual sense of the uncertainty in outcomes, Figures 2 and 3 in the paper show the 5th and 95th percentiles, as well as the expected values.
• The model divides the world into four World Bank income levels (low, lower-middle, upper-middle, and high) to capture important differences in costs and poliovirus transmission.
• Details of the model appear in a separate paper that explores uncertainty and sensitivity analyses of the model.
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• Consistent with standard methods for cost-effectiveness analysis, we report numerical estimates only for positive incremental cost AND incremental effectiveness estimates. In the case of positive incremental effectiveness estimates but negative incremental costs, we report the comparison between the alternative and comparator policies as “cost and life saving.” In the case of positive incremental costs but negative incremental effectiveness estimates, we report that the alternative is “dominated” by the comparator. For negative incremental cost and incremental effectiveness estimates, we report the comparison as “cost saving but life costing.”
• In the case of non-numerical cost-effectiveness ratios, the incremental net benefit estimate provides a numerical value of the policy comparison in monetary terms. To express prevented polio disease in monetary terms, we assigned each disability-adjusted life-year averted due to prevention of a paralytic polio case a value equal to the average annual per-capita gross national income in an income group (see uncertainty and sensitivity analyses for details and discussion of the impact of altering this assumption on the incremental net benefit estimates).
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