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