Economics of Eradication: Counting on the Polio Experience  Free

(See the Major Article by Badizadegan et al, on pages 1309–18.)

The historic battle for global polio eradication spanning more than three decades may have reached a decisive juncture in 2021–2022 with wild polio virus cases in single digits in Pakistan and Afghanistan [1]. Despite the unprecedented challenges posed by the coronavirus disease 2019 (COVID-19) pandemic, the remarkable decline in wild poliovirus transmission in the only two remaining polio endemic countries is a testament to the success of strategies implemented by the Global Polio Eradication Initiative (GPEI) to interrupt transmission of the virus with sustained immunization efforts. However, significant challenges remain in the final stretch to achieve the global eradication program’s goal of permanently stopping transmission of all polioviruses everywhere in the world [2]. The surge in circulating vaccine-derived poliovirus (cVDPV) outbreaks across the World Health Organization (WHO) African Region and beyond, and the recent importation of wild poliovirus into a polio-free country such as Malawi highlight the complexities that lie ahead before reaching the finishing line of indefinitely sustaining a world free of all forms of polioviruses. In the final phases of this long-drawn-out global effort to eradicate a human disease from Earth for only the second time, the scientific, social, and political complexities to interrupt all forms of poliovirus transmission will have to be carefully assessed with the characterization of economic dimensions of the global polio eradication strategies through the endgame and beyond.

As the new global strategy (2022–2026) for polio eradication is adopted and implemented, understanding the impact of investments over past decades by the GPEI to prevent children from becoming paralyzed is of paramount importance [3]. For this exercise, it is also important to use health economic models that are well calibrated and adjusted to the complex and interdependent factors relevant to polio eradication (eg, virus transmission, population immunity, and vaccine choice) and the overall economic impact of each of these variables for global policy making. An integrated modeling approach such as the one reported by Badizadegan et al in this issue of The Journal of Infectious Diseases [4] should be well placed to capture the interdependencies of different global health strategies relative to estimates of cases prevented with minimal effect from variations based on a few specific factors, for example.

Using this integrated global model approach, Badizadegan et al estimate that compared with a scenario of no availability of polio vaccines, the effective application of vaccination strategies in the era before the World Health Assembly resolution (1960–1987) and the time since (1988–2021) might have prevented 5 million and 24 million children, respectively, from becoming paralyzed from wild polioviruses from a global perspective [4]. Moving a step further and focusing on the era following the launch of GPEI in 1988, the estimates suggest approximately 2.5–6 million children have been protected from paralytic poliomyelitis thanks to concerted GPEI-assisted large-scale immunization efforts and mass vaccination campaigns with a range of different types (trivalent, bivalent, monovalent) of oral polio vaccines (OPVs) compared with a world without these interventions. In this context, it is important to emphasize that the overall population-level impact of the supplementary immunization activities (SIAs), surveillance initiatives, containment principles, and other strategies implemented by the GPEI and its partners go above and beyond paralysis prevention as outbreaks are prevented or stopped and the population at risk of virus transmission is minimized.

Characterization of polio outbreaks and their impact on individuals and communities over time is a complex task. This is particularly relevant given the trend of transnational polio outbreaks and their impact on the overall burden of paralytic cases and infections, especially in countries that traditionally have behaved as amplifying geographies and thereby having a large but indirect, and often poorly measured, impact on public health interventions and health economics of countries at risk of reinfection and resurgence. In addition, the outcome indicator may not be limited only to prevention of paralysis. Deaths attributed to polio can be significant as the estimated case-fatality rate of poliovirus is 1%–5% and is often higher when adults are affected in previously polio-free geographies. Thus, in a routine immunization-only program, polio could have a significant public health impact in the absence of other aspects of GPEI interventions such as SIAs and mop-up campaigns.

No matter how small the geographic extent of wild poliovirus endemicity, if the virus is anywhere in the world, it is a threat to the polio-free status of countries everywhere, given the historic trends of poliovirus importations, outbreaks, and reestablishment of circulation. The introduction of wild poliovirus type 1 into Malawi more than 5 years after the absence of any wild poliovirus in Africa is an example of the risks of not finishing the job of eradicating polio globally. Sporadic outbreak responses with mass vaccination campaigns are expensive and resource intensive, especially in the context of suboptimal routine immunization coverage in underserved communities. In addition, unique endgame challenges related to cVDPVs evolving in areas with persistently poor population immunity and the risk of reintroduction of virus circulation from immune-deficient poliovirus excretors necessitate forward-looking investments in preventive and therapeutic tools. This includes use of novel vaccines that have a lower risk of reversion and thus a lower risk of regaining the virulence and transmissibility of wild viruses, identifying safer options for vaccine manufacturing to minimize risk of containment failure, enhancing ways to detect virus early in a community to facilitate interruption of transmission, and developing therapeutic tools to eliminate chronic carriage and shedding of vaccine or wild viruses from immune-deficient individuals to minimize the risks of maintaining eradication status [2, 5]. The GPEI and its partners have demonstrated the ability to keep eradication-enabling innovations on an accelerated track while ensuring that available and affordable vaccines reach the most vulnerable population. But sustaining these efforts while strengthening the essential immunization practices and maintaining wider donor interest will be key to maintaining momentum in the final stretch. Future health economic assessments will also need to focus on investments in the novel tools and technological solutions discussed above that could be necessary to achieve and maintain eradication, given the evolving challenges of the polio eradication endgame.

Despite the efforts to address methodological issues for such modeling exercises, there are uncertainties and heterogeneity around the source data such as the ones related to polio surveillance and case definitions in different geographies over time, including serotype-specific variance of case-infection ratio impacting some of the earlier annual estimates of the burden of paralytic cases from wild polioviruses. On the other hand, it is difficult to quantify the likely impact of the GPEI on global health preparedness and the cascading effects on lives and dollars saved. Repurposing the GPEI infrastructure for initial public health responses to Ebola and the COVID-19 pandemic and developing novel oral polio vaccine type-2 (nOPV2)—the first-ever vaccine for use through Emergency Use Listing—are a few recent examples of efforts transcending the polio-specific spectrum to pave the way for larger public health efforts. As acknowledged in the narrative, such impacts are outside of the scope of this analysis but may have substantial economic and health policy benefits over time. A more comprehensive approach to incorporate these interdependencies across different disease spectra would put the broader impact and legacy of such unique global initiatives into context, beyond just the numbers.

Finally, it needs to be emphasized that despite the health and economic gains made through the polio eradication effort, which have led to the elimination of wild polioviruses from all but one WHO Region and the global eradication of two out of the three serotypes of wild polioviruses, we should neither underestimate the challenges ahead of us nor prematurely redirect resources currently devoted to polio to other health programs. Stopping the eradication effort now could have disastrous consequences, including a global resurgence of poliovirus transmission. Therefore, it is critical that we build on the progress made, recognize the complexities ahead, and focus on forward-looking investments that are in sync with the current global situation to terminate the last chains of transmission of all forms of polioviruses everywhere and forever.

Note

Financial support. No financial support was received for this work.

References

Author notes