BACKGROUND: The Global Polio Eradication Initiative (GPEI) Strategic Plan for 2019-2023 includes commitments to monitor the quality of immunization campaigns using lot quality assurance sampling surveys (LQAS) and to support poliovirus surveillance in Pakistan and Afghanistan. METHODS: We analyzed LQAS and poliovirus surveillance data between 2016 and 2020, which included both acute flaccid paralysis (AFP) case-based detection and the continued expansion of environmental surveillance (ES). Using updated estimates for unit costs, we explore the costs of different options for future poliovirus monitoring and surveillance for Pakistan and Afghanistan. RESULTS: The relative value of the information provided by campaign quality monitoring and surveillance remains uncertain and depends on the design, implementation, and performance of the systems. Prospective immunization campaign quality monitoring (through LQAS) and poliovirus surveillance will require tens of millions of dollars each year for the foreseeable future for Pakistan and Afghanistan. CONCLUSIONS: LQAS campaign monitoring as currently implemented in Pakistan and Afghanistan provides limited and potentially misleading information about immunization quality. AFP surveillance in Pakistan and Afghanistan provides the most reliable evidence of transmission, whereas ES provides valuable supplementary information about the extent of transmission in the catchment areas represented at the time of sample collection.

The Global Polio Eradication Initiative (GPEI) faces substantial challenges with managing outbreaks of serotype 2 circulating vaccine-derived polioviruses (cVDPV2s) in 2021. A full five years after the globally coordinated removal of serotype 2 oral poliovirus vaccine (OPV2) from trivalent oral poliovirus vaccine (tOPV) for use in national immunization programs, cVDPV2s did not die out. Since OPV2 cessation, responses to outbreaks caused by cVDPV2s mainly used serotype 2 monovalent OPV (mOPV2) from a stockpile. A novel vaccine developed from a genetically stabilized OPV2 strain (nOPV2) promises to potentially facilitate outbreak response with lower prospective risks, although its availability and properties in the field remain uncertain. Using an established global poliovirus transmission model and building on a related analysis that characterized the impacts of disruptions in GPEI activities caused by the COVID-19 pandemic, we explore the implications of trade-offs associated with delaying outbreak response to avoid using mOPV2 by waiting for nOPV2 availability (or equivalently, delayed responses waiting for national validation of meeting the criteria for nOPV2 initial use). Consistent with prior modeling, responding as quickly as possible with available mOPV2 promises to reduce the expected burden of disease in the outbreak population and to reduce the chances for the outbreak virus to spread to other areas. Delaying cVDPV2 outbreak response (e.g., modeled as no response January-June 2021) to wait for nOPV2 can considerably increase the total expected cases (e.g., by as many as 1,300 cVDPV2 cases in the African region during 2021-2023) and increases the likelihood of triggering the need to restart widescale preventive use of an OPV2-containing vaccine in national immunization programs that use OPV. Countries should respond to any cVDPV2 outbreaks quickly with rounds that achieve high coverage using any available OPV2, and plan to use nOPV2, if needed, once it becomes widely available based on evidence that it is as effective but safer in populations than mOPV2.

In early 2020, the COVID-19 pandemic led to substantial disruptions in global activities. The disruptions also included intentional and unintentional reductions in health services, including immunization campaigns against the transmission of wild poliovirus (WPV) and persistent serotype 2 circulating vaccine-derived poliovirus (cVDPV2). Building on a recently updated global poliovirus transmission and Sabin-strain oral poliovirus vaccine (OPV) evolution model, we explored the implications of immunization disruption and restrictions of human interactions (i.e., population mixing) on the expected incidence of polio and on the resulting challenges faced by the Global Polio Eradication Initiative (GPEI). We demonstrate that with some resumption of activities in the fall of 2020 to respond to cVDPV2 outbreaks and full resumption on January 1, 2021 of all polio immunization activities to pre-COVID-19 levels, the GPEI could largely mitigate the impact of COVID-19 to the delays incurred. The relative importance of reduced mixing (leading to potentially decreased incidence) and reduced immunization (leading to potentially increased expected incidence) depends on the timing of the effects. Following resumption of immunization activities, the GPEI will likely face similar barriers to eradication of WPV and elimination of cVDPV2 as before COVID-19. The disruptions from the COVID-19 pandemic may further delay polio eradication due to indirect effects on vaccine and financial resources.

BACKGROUND: Pakistan and Afghanistan remain the only reservoirs of wild poliovirus transmission. Prior modeling suggested that before the COVID-19 pandemic, plans to stop the transmission of serotype 1 wild poliovirus (WPV1) and persistent serotype 2 circulating vaccine-derived poliovirus (cVDPV2) did not appear on track to succeed. METHODS: We updated an existing poliovirus transmission and Sabin-strain oral poliovirus vaccine (OPV) evolution model for Pakistan and Afghanistan to characterize the impacts of immunization disruptions and restrictions on human interactions (i.e., population mixing) due to the COVID-19 pandemic. We also consider different options for responding to outbreaks and for preventive supplementary immunization activities (SIAs). RESULTS: The modeling suggests that with some resumption of activities in the fall of 2020 to respond to cVDPV2 outbreaks and full resumption on January 1, 2021 of all polio immunization activities to pre-COVID-19 levels, Pakistan and Afghanistan would remain off-track for stopping all transmission through 2023 without improvements in quality. CONCLUSIONS: Using trivalent OPV (tOPV) for SIAs instead of serotype 2 monovalent OPV (mOPV2) offers substantial benefits for ending the transmission of both WPV1 and cVDPV2, because tOPV increases population immunity for both serotypes 1 and 2 while requiring fewer SIA rounds, when effectively delivered in transmission areas.

After the globally coordinated cessation of any serotype of oral poliovirus vaccine (OPV), some risks remain from undetected, existing homotypic OPV-related transmission and/or restarting transmission due to several possible reintroduction risks. The Global Polio Eradication Initiative (GPEI) coordinated global cessation of serotype 2-containing OPV (OPV2) in 2016. Following OPV2 cessation, the GPEI and countries implemented activities to withdraw all the remaining trivalent OPV, which contains all three poliovirus serotypes (i.e., 1, 2, and 3), from the supply chain and replace it with bivalent OPV (containing only serotypes 1 and 3). However, as of early 2020, monovalent OPV2 use for outbreak response continues in many countries. In addition, outbreaks observed in 2019 demonstrated evidence of different types of risks than previously modeled. We briefly review the 2019 epidemiological experience with serotype 2 live poliovirus outbreaks and propose a new risk for unexpected OPV introduction for inclusion in global modeling of OPV cessation. Using an updated model of global poliovirus transmission and OPV evolution with and without consideration of this new risk, we explore the implications of the current global situation with respect to the likely need to restart preventive use of OPV2 in OPV-using countries. Simulation results without this new risk suggest OPV2 restart will likely need to occur (81% of 100 iterations) to manage the polio endgame based on the GPEI performance to date with existing vaccine tools, and with the new risk of unexpected OPV introduction the expected OPV2 restart probability increases to 89%. Contingency planning requires new OPV2 bulk production, including genetically stabilized OPV2 strains.

As the vaccine of choice for the Global Polio Eradication Initiative (GPEI), oral poliovirus vaccine (OPV) is inexpensive, easy to administer, and can provide good protection against poliomyelitis and poliovirus infection, through durable humoral immunity and induction of intestinal mucosal immunity. Even though trivalent OPV is a safe and effective vaccine and has a remarkable disease elimination record, all 3 strains are live attenuated RNA viruses capable of genetic mutation during replication. This means that polioviruses in OPV can undergo genetic changes in vaccine recipients to reverse attenuation. This inherent instability represents a key disadvantage of OPV that is manifest in some of the current polio eradication challenges.

The past decade began with a great deal of promise that after nearly 50 years of measles vaccine use to combat one of the major causes of global child mortality, a world without measles was finally in sight [1]. In 1980, before widespread global use of measles vaccine, an estimated 2.6 million measles deaths occurred worldwide. At the beginning of the 21st century, to accelerate the reduction in measles cases achieved by vaccination, a new strategy to deliver at least 2 doses of measles-containing vaccine (MCV) to all children, either through routine immunization services or supplementary immunization activities (SIAs), and to improve measles surveillance was launched by the founding partners of a new global Measles Initiative—the World Health Organization (WHO), the United Nations Children’s Fund (UNICEF), the Centers for Disease Control and Prevention, the United Nations Foundation, and the American Red Cross (the initiative was renamed the Measles and Rubella Initiative in 2012) [2]. During the first decade of this century, this initiative supported the vaccination of > 900 million children in SIAs and led to a decrease in global mortality attributed to measles by an impressive 78%, from an estimated 733 000 deaths in 2000 to 164 000 in 2008, as well as an increase in MCV first-dose routine immunization coverage (MCV1) from 72% to 85% during 2000–2010 [1]. Moreover, reductions in measles mortality accounted for a remarkable 23% of the overall estimated global decline in all-cause child mortality from 1990 to 2008 [3]. In the United States (US), measles was declared eliminated in 2000 as a result of sustained interruption of transmission.

Nearly 20 years after the year 2000 target for global wild poliovirus (WPV) eradication, live polioviruses continue to circulate with all three serotypes posing challenges for the polio endgame. We updated a global differential equation-based poliovirus transmission and stochastic risk model to include programmatic and epidemiological experience through January 2020. We used the model to explore the likely dynamics of poliovirus transmission for 2019-2023, which coincides with a new Global Polio Eradication Initiative Strategic Plan. The model stratifies the global population into 72 blocks, each containing 10 subpopulations of approximately 10.7 million people. Exported viruses go into subpopulations within the same block and within groups of blocks that represent large preferentially mixing geographical areas (e.g., continents). We assign representative World Bank income levels to the blocks along with polio immunization and transmission assumptions, which capture some of the heterogeneity across countries while still focusing on global poliovirus transmission dynamics. We also updated estimates of reintroduction risks using available evidence. The updated model characterizes transmission dynamics and resulting polio cases consistent with the evidence through 2019. Based on recent epidemiological experience and prospective immunization assumptions for the 2019-2023 Strategic Plan, the updated model does not show successful eradication of serotype 1 WPV by 2023 or successful cessation of oral poliovirus vaccine serotype 2-related viruses.

BACKGROUND: The pace of global progress must increase if the Global Vaccine Action Plan (GVAP) goals are to be achieved by 2020. We administered a two-phase survey to key immunization stakeholders to assess the utility and application of GVAP, including how it has impacted country immunization programs, and to find ways to strengthen the next 10-year plan. METHODS: For the Phase I survey, an online questionnaire was sent to global immunization stakeholders in summer 2017. The Phase II survey was sent to regional and national immunization stakeholders in summer 2018, including WHO Regional Advisors on Immunization, Expanded Programme on Immunization managers, and WHO and UNICEF country representatives from 20 countries. Countries were selected based on improvements (10) versus decreases (10) in DTP3 coverage from 2010 to 2016. RESULTS: Global immunization stakeholders (n=38) cite global progress in improving vaccine delivery (88%) and engaging civil society organizations as advocates for vaccines (83%). Among regional and national immunization stakeholders (n=58), 70% indicated reaching mobile and underserved populations with vaccination activities as a major challenge. The top ranked activities for helping country programs achieve progress toward GVAP goals include improved monitoring of vaccination coverage and upgrading disease surveillance systems. Most respondents (96%) indicated GVAP as useful for determining immunization priorities and 95% were supportive of a post-2020 GVAP strategy. CONCLUSIONS: Immunization stakeholders see GVAP as a useful tool, and there is cause for excitement as the global immunization community looks toward the next decade of vaccines. The next 10-year plan should attempt to increase political will, align immunization activities with other health system agendas, and address important issues like reaching mobile/migrant populations and improving data reporting systems.

In April 2016, all 155 oral poliovirus vaccine (OPV)–using countries and territories in the world discontinued use of Sabin poliovirus type 2 by switching from trivalent OPV (tOPV) to bivalent OPV (bOPV), containing Sabin poliovirus types 1 and 3, in their national immunization schedules [1]. This event was the largest recall of a medicinal product in history and the fastest introduction of a new vaccine—bOPV. At the same time, all OPV-using countries attempted to introduce at least 1 dose of inactivated poliovirus vaccine (IPV) into the childhood immunization schedule for risk mitigation, primarily to minimize the number of paralytic poliomyelitis cases, should poliovirus type 2 be reintroduced or emerge [2].

Due to security, access, and programmatic challenges in areas of Pakistan and Afghanistan, both countries continue to sustain indigenous wild poliovirus (WPV) transmission and threaten the success of global polio eradication and oral poliovirus vaccine (OPV) cessation. We fitted an existing differential-equation-based poliovirus transmission and OPV evolution model to Pakistan and Afghanistan using four subpopulations to characterize the well-vaccinated and undervaccinated subpopulations in each country. We explored retrospective and prospective scenarios for using inactivated poliovirus vaccine (IPV) in routine immunization or supplemental immunization activities (SIAs). The undervaccinated subpopulations sustain the circulation of serotype 1 WPV and serotype 2 circulating vaccine-derived poliovirus. We find a moderate impact of past IPV use on polio incidence and population immunity to transmission mainly due to (1) the boosting effect of IPV for individuals with preexisting immunity from a live poliovirus infection and (2) the effect of IPV-only on oropharyngeal transmission for individuals without preexisting immunity from a live poliovirus infection. Future IPV use may similarly yield moderate benefits, particularly if access to undervaccinated subpopulations dramatically improves. However, OPV provides a much greater impact on transmission and the incremental benefit of IPV in addition to OPV remains limited. This study suggests that despite the moderate effect of using IPV in SIAs, using OPV in SIAs remains the most effective means to stop transmission, while limited IPV resources should prioritize IPV use in routine immunization.

Why not take advantage of the experience and infrastructure developed to eradicate polio to pursue the elimination of measles and rubella, which is within our grasp [1, 2] ? The importance of eliminating measles, rubella and congenital rubella syndrome (CRS) is now recognized globally. Measles is still a leading cause of child deaths worldwide (>130,000 deaths per year) despite availability of an effective and cheap vaccine for more than 50 years [3]. Given the visibility of birth defects caused by Zika virus, we need to remember that rubella virus is still the leading infectious disease cause of congenital birth defects (CRS) globally, and the unfinished agenda of preventing through rubella vaccination the >100,000 CRS cases per year still occurring worldwide [4, 5]. So the measles and rubella vaccines continue to be “weapons of mass salvation” against these potentially deadly diseases.

The Global Polio Eradication Initiative (GPEI) has been in operation since 1988, now spends $1 billion annually, and operates through thousands of staff and millions of volunteers in dozens of countries. It has brought polio to the brink of eradication. After eradication is achieved, what should happen to the substantial assets, capabilities, and lessons of the GPEI? To answer this question, an extensive process of transition planning is underway. There is an absolute need to maintain and mainstream some of the functions, to keep the world polio-free. There is also considerable risk - and, if seized, substantial opportunity - for other health programs and priorities. And critical lessons have been learned that can be used to address other health priorities. Planning has started in the 16 countries where GPEI's footprint is the greatest and in the program's 5 core agencies. Even though poliovirus transmission has not yet been stopped globally, this planning process is gaining momentum, and some plans are taking early shape. This is a complex area of work - with difficult technical, financial, and political elements. There is no significant precedent. There is forward motion and a willingness on many sides to understand and address the risks and to explore the opportunities. Very substantial investments have been made, over 30 years, to eradicate a human pathogen from the world for the second time ever. Transition planning represents a serious intent to responsibly bring the world's largest global health effort to a close and to protect and build upon the investment in this effort, where appropriate, to benefit other national and global priorities. Further detailed technical work is now needed, supported by broad and engaged debate, for this undertaking to achieve its full potential.

Background. The Polio Eradication and Endgame Strategic Plan (PEESP) established a target that at least 50% of the time of personnel receiving funding from the Global Polio Eradication Initiative (GPEI) for polio eradication activities (hereafter, "GPEI-funded personnel") should be dedicated to the strengthening of immunization systems. This article describes the self-reported profile of how GPEI-funded personnel allocate their time toward immunization goals and activities beyond those associated with polio, the training they have received to conduct tasks to strengthen routine immunization systems, and the type of tasks they have conducted. Methods. A survey of approximately 1000 field managers of frontline GPEI-funded personnel was conducted by Boston Consulting Group in the 10 focus countries of the PEESP during 2 phases, in 2013 and 2014, to determine time allocation among frontline staff. Country-specific reports on the training of GPEI-funded personnel were reviewed, and an analysis of the types of tasks that were reported was conducted. Results. A total of 467 managers responded to the survey. Forty-seven percent of the time (range, 23%-61%) of GPEI-funded personnel was dedicated to tasks related to strengthening immunization programs, other than polio eradication. Less time was spent on polio-associated activities in countries that had already interrupted wild poliovirus (WPV) transmission, compared with findings for WPV-endemic countries. All countries conducted periodic trainings of the GPEI-funded personnel. The types of non-polio-related tasks performed by GPEI-funded personnel varied among countries and included surveillance, microplanning, newborn registration and defaulter tracing, monitoring of routine immunization activities, and support of district immunization task teams, as well as promotion of health behaviors, such as clean-water use and good hygiene and sanitation practices. Conclusion. In all countries, GPEI-funded personnel perform critical tasks in the strengthening of routine immunization programs and the control of measles and rubella. In certain countries with very weak immunization systems, GPEI-funded personnel provide critical support for the immunization programs, and sudden discontinuation of their employment would potentially disrupt the immunization programs in their countries and create a setback in capacity and effectiveness that would put children at higher risk for vaccine-preventable diseases.

On November 23, 1965, President Lyndon Johnson announced plans for a 5-year smallpox eradication and measles control program in West Africa that enabled the Centers for Disease Control and Prevention (CDC) to establish a Smallpox Eradication Program in January 1966. Since then, CDC’s global immunization endeavors have encompassed global smallpox eradication, the establishment and growth of the Expanded Program on Immunization (EPI) to strengthen national immunization programs, global efforts to eradicate polio and eliminate measles and rubella, and vaccine introduction into national immunization schedules beyond the original 6 EPI vaccines. CDC has provided scientific leadership, evidence-based guidance, and programmatic strategies to build public health infrastructure around the world, needed to achieve and measure the impact of these global immunization initiatives. This article marks the 50th anniversary of CDC’s global immunization leadership, highlights key historical events, and provides an overview of CDC’s future directions. | Before 1955, smallpox and diphtheria-tetanus-pertussis vaccines were the only routinely recommended childhood vaccines in the United States. The roots of global immunization at CDC began after clinical trials for the Salk inactivated polio vaccine (IPV) in 1954. After investigators announced on April 12, 1955, that Salk IPV was safe and effective, large-scale vaccination campaigns were implemented across the United States, and IPV was set to join diphtheria-tetanus-pertussis and smallpox vaccines in the childhood vaccination schedule. However, improperly prepared IPV by Cutter Pharmaceuticals used for the vaccination campaigns led to 200 cases of paralysis and 10 deaths.1

OBJECTIVE: To examine the impact of different bivalent oral poliovirus vaccine (bOPV) supplemental immunization activity (SIA) strategies on population immunity to serotype 1 and 3 poliovirus transmission and circulating vaccine-derived poliovirus (cVDPV) risks before and after globally-coordinated cessation of serotype 1 and 3 oral poliovirus vaccine (OPV13 cessation). METHODS: We adapt mathematical models that previously informed vaccine choices ahead of the trivalent oral poliovirus vaccine to bOPV switch to estimate the population immunity to serotype 1 and 3 poliovirus transmission needed at the time of OPV13 cessation to prevent subsequent cVDPV outbreaks. We then examine the impact of different frequencies of SIAs using bOPV in high risk populations on population immunity to serotype 1 and 3 transmission, on the risk of serotype 1 and 3 cVDPV outbreaks, and on the vulnerability to any imported bOPV-related polioviruses. RESULTS: Maintaining high population immunity to serotype 1 and 3 transmission using bOPV SIAs significantly reduces 1) the risk of outbreaks due to imported serotype 1 and 3 viruses, 2) the emergence of indigenous cVDPVs before or after OPV13 cessation, and 3) the vulnerability to bOPV-related polioviruses in the event of non-synchronous OPV13 cessation or inadvertent bOPV use after OPV13 cessation. CONCLUSION: Although some reduction in global SIA frequency can safely occur, countries with suboptimal routine immunization coverage should each continue to conduct at least one annual SIA with bOPV, preferably more, until global OPV13 cessation. Preventing cVDPV risks after OPV13 cessation requires investments in bOPV SIAs now through the time of OPV13 cessation.

Over the past 50 years, the use of vaccines led to significant decreases in the global burdens of measles and rubella, motivated at least in part by the successive development of global control and elimination targets. The Global Vaccine Action Plan (GVAP) includes specific targets for regional elimination of measles and rubella in five of six regions of the World Health Organization by 2020. Achieving the GVAP measles and rubella goals will require significant immunization efforts and associated financial investments and political commitments. Planning and budgeting for these efforts can benefit from learning some important lessons from the Global Polio Eradication Initiative (GPEI). Following an overview of the global context of measles and rubella risks and discussion of lessons learned from the GPEI, we introduce the contents of the special issue on modeling and managing the risks of measles and rubella. This introduction describes the synthesis of the literature available to support evidence-based model inputs to support the development of an integrated economic and dynamic disease transmission model to support global efforts to optimally manage these diseases globally using vaccines.

BACKGROUND: Following successful eradication of wild polioviruses and planned globally-coordinated cessation of oral poliovirus vaccine (OPV), national and global health leaders may need to respond to outbreaks from reintroduced live polioviruses, particularly vaccine-derived polioviruses (VDPVs). Preparing outbreak response plans and assessing potential vaccine needs from an emergency stockpile require consideration of the different national risks and conditions as they change with time after OPV cessation. METHODS: We used an integrated global model to consider several key issues related to managing poliovirus risks and outbreak response, including the time interval during which monovalent OPV (mOPV) can be safely used following homotypic OPV cessation; the timing, quality, and quantity of rounds required to stop transmission; vaccine stockpile needs; and the impacts of vaccine choices and surveillance quality. We compare the base case scenario that assumes aggressive outbreak response and sufficient mOPV available from the stockpile for all outbreaks that occur in the model, with various scenarios that change the outbreak response strategies. RESULTS: Outbreak response after OPV cessation will require careful management, with some circumstances expected to require more and/or higher quality rounds to stop transmission than others. For outbreaks involving serotype 2, using trivalent OPV instead of mOPV2 following cessation of OPV serotype 2 but before cessation of OPV serotypes 1 and 3 would represent a good option if logistically feasible. Using mOPV for outbreak response can start new outbreaks if exported outside the outbreak population into populations with decreasing population immunity to transmission after OPV cessation, but failure to contain outbreaks resulting in exportation of the outbreak poliovirus may represent a greater risk. The possibility of mOPV use generating new long-term poliovirus excretors represents a real concern. Using the base case outbreak response assumptions, we expect over 25 % probability of a shortage of stockpiled filled mOPV vaccine, which could jeopardize the achievement of global polio eradication. For the long term, responding to any poliovirus reintroductions may require a global IPV stockpile. Despite the risks, our model suggests that good risk management and response strategies can successfully control most potential outbreaks after OPV cessation. CONCLUSIONS: Health leaders should carefully consider the numerous outbreak response choices that affect the probability of successfully managing poliovirus risks after OPV cessation.

Global efforts to eliminate measles and rubella can be combined with other actions to accelerate the strengthening of health systems in developing countries. However, there are several challenges standing in the way of successfully combining measles and rubella vaccination campaigns with health systems strengthening. Those challenges include the following: achieving universal vaccine coverage while integrating the initiative with other primary care strategies and developing the necessary health system resilience to confront emergencies, ensuring epidemiological and laboratory surveillance of vaccine-preventable diseases, developing the human resources needed to effectively manage and implement national strategies, increasing community demand for health services, and obtaining long-term political support. We describe lessons learned from the successful elimination of measles and rubella in the Americas and elsewhere that strive to strengthen national health systems to both improve vaccine uptake and confront emerging threats. The elimination of measles and rubella provides opportunities for nations to strengthen health systems and thus to both reduce inequities and ensure national health security.

The world is closer than ever to achieving global polio eradication, with record-low polio cases in 2015 and the impending prospect of a polio-free Africa. Tens of millions of volunteers, social mobilizers, and health workers have participated in the Global Polio Eradication Initiative. The program contributes to efforts to deliver other health benefits, including health systems strengthening. As the initiative nears completion after more than twenty-five years, it becomes critical to document and transition the knowledge, lessons learned, assets, and infrastructure accumulated by the initiative to address other health goals and priorities. The primary goals of this process, known as polio legacy transition planning, are both to protect a polio-free world and to ensure that investments in polio eradication will contribute to other health goals after polio is completely eradicated. The initiative is engaged in an extensive transition process of consultations and planning at the global, regional, and country levels. A successful completion of this process will result in a well-planned and -managed conclusion of the initiative that will secure the global public good gained by ending one of the world's most devastating diseases and ensure that these investments provide public health benefits for years to come.

In the United States during the 1950's, polio was on the forefront of every provider and caregiver's mind. Today, most providers in the United States have never seen a case. The Global Polio Eradication Initiative (GPEI), which began in 1988 has reduced the number of cases by over 99%. The world is closer to achieving global eradication of polio than ever before but as long as poliovirus circulates anywhere in the world, every country is vulnerable. The global community can support the polio eradication effort through continued vaccination, surveillance, enforcing travel regulations and contributing financial support, partnerships and advocacy.

BACKGROUND: The Global Polio Eradication Initiative plans for coordinated cessation of oral poliovirus vaccine (OPV) after interrupting all wild poliovirus (WPV) transmission, but many questions remain related to long-term poliovirus risk management policies. METHODS: We used an integrated dynamic poliovirus transmission and stochastic risk model to simulate possible futures and estimate the health and economic outcomes of maintaining the 2013 status quo of continued OPV use in most developing countries compared with OPV cessation policies with various assumptions about global inactivated poliovirus vaccine (IPV) adoption. RESULTS: Continued OPV use after global WPV eradication leads to continued high costs and/or high cases. Global OPV cessation comes with a high probability of at least one outbreak, which aggressive outbreak response can successfully control in most instances. A low but non-zero probability exists of uncontrolled outbreaks following a poliovirus reintroduction long after OPV cessation in a population in which IPV-alone cannot prevent poliovirus transmission. We estimate global incremental net benefits during 2013-2052 of approximately $16 billion (US$2013) for OPV cessation with at least one IPV routine immunization dose in all countries until 2024 compared to continued OPV use, although significant uncertainty remains associated with the frequency of exportations between populations and the implementation of long term risk management policies. CONCLUSIONS: Global OPV cessation offers the possibility of large future health and economic benefits compared to continued OPV use. Long-term poliovirus risk management interventions matter (e.g., IPV use duration, outbreak response, containment, continued surveillance, stockpile size and contents, vaccine production site requirements, potential antiviral drugs, and potential safer vaccines) and require careful consideration. Risk management activities can help to ensure a low risk of uncontrolled outbreaks and preserve or further increase the positive net benefits of OPV cessation. Important uncertainties will require more research, including characterizing immunodeficient long-term poliovirus excretor risks, containment risks, and the kinetics of outbreaks and response in an unprecedented world without widespread live poliovirus exposure.

BACKGROUND: Frequent supplemental immunization activities (SIAs) with the oral poliovirus vaccine (OPV) represent the primary strategy to interrupt poliovirus transmission in the last endemic areas. MATERIALS AND METHODS: Using a differential-equation based poliovirus transmission model tailored to high-risk areas in Nigeria, we perform one-way and multi-way sensitivity analyses to demonstrate the impact of different assumptions about routine immunization (RI) and the frequency and quality of SIAs on population immunity to transmission and persistence or emergence of circulating vaccine-derived polioviruses (cVDPVs) after OPV cessation. RESULTS: More trivalent OPV use remains critical to avoid serotype 2 cVDPVs. RI schedules with or without inactivated polio vaccine (IPV) could significantly improve population immunity if coverage increases well above current levels in under-vaccinated subpopulations. Similarly, the impact of SIAs on overall population immunity and cVDPV risks depends on their ability to reach under-vaccinated groups (i.e., SIA quality). Lower SIA coverage in the under-vaccinated subpopulation results in a higher frequency of SIAs needed to maintain high enough population immunity to avoid cVDPVs after OPV cessation. CONCLUSIONS: National immunization program managers in northwest Nigeria should recognize the benefits of increasing RI and SIA quality. Sufficiently improving RI coverage and improving SIA quality will reduce the frequency of SIAs required to stop and prevent future poliovirus transmission. Better information about the incremental costs to identify and reach under-vaccinated children would help determine the optimal balance between spending to increase SIA and RI quality and spending to increase SIA frequency.

Most poliovirus infections occur with no symptoms and this leads to the possibility of silent circulation, which complicates the confirmation of global goals to permanently end poliovirus transmission. Previous simple models based on hypothetical populations assumed perfect detection of symptomatic cases and suggested the need to observe no paralytic cases from wild polioviruses (WPVs) for approximately 3-4 years to achieve 95% confidence about eradication, but the complexities in real populations and the imperfect nature of surveillance require consideration. Methods: We revisit the probability of undetected poliovirus circulation using a more comprehensive model that reflects the conditions in a number of places with different characteristics related to WPV transmission, and we model the actual environmental WPV detection that occurred in Israel in 2013. We consider the analogous potential for undetected transmission of circulating vaccine-derived polioviruses. The model explicitly accounts for the impact of different vaccination activities before and after the last detected case of paralytic polio, different levels of surveillance, variability in transmissibility and neurovirulence among serotypes, and the possibility of asymptomatic participation in transmission by previously-vaccinated or infected individuals. Results: We find that prolonged circulation in the absence of cases and thus undetectable by case-based surveillance may occur if vaccination keeps population immunity close to but not over the threshold required for the interruption of transmission, as may occur in northwestern Nigeria for serotype 2 circulating vaccine-derived poliovirus in the event of insufficient tOPV use. Participation of IPV-vaccinated individuals in asymptomatic fecal-oral transmission may also contribute to extended transmission undetectable by case-based surveillance, as occurred in Israel. We also find that gaps or quality issues in surveillance could significantly reduce confidence about actual disruption. Maintaining high population immunity and high-quality surveillance for several years after the last detected polio cases will remain critical elements of the polio end game. Conclusions: Countries will need to maintain vigilance in their surveillance for polioviruses and recognize that their risks of undetected circulation may differ as a function of their efforts to manage population immunity and to identify cases or circulating live polioviruses.

Achieving global polio eradication requires that global stakeholders coordinate and cooperate to invest human and financial resources in interventions that prevent virus transmission. Reaching this goal depends on effective tools and interventions, and their optimal use. Poliovirus transmission occurs in a complex global system with rapidly evolving viruses that readily cross international borders. The U.S. Centers for Disease Control and Prevention, one of four spearheading partners of the Global Polio Eradication Initiative (GPEI), initiated a collaboration with Kid Risk, Inc. to develop and apply integrated analytical models to answer high-stakes policy questions related to managing the risks of polioviruses with consideration of human health and economic outcomes. Over the last decade, the collaboration innovatively combined numerous operations research and management science tools, including simulation, decision and risk analysis, system dynamics, and optimization to help policy makers understand and quantify the implications of their choices. These integrated modeling efforts helped motivate faster responses to polio outbreaks, leading to a global resolution and significantly reduced response time and outbreak sizes. Insights from the models also underpinned a 192-country resolution to coordinate global cessation of the use of one of the two vaccines after wild poliovirus eradication (i.e., allowing continued use of the other vaccine as desired). Finally, the model results helped us to make the economic case for a continued commitment to polio eradication by quantifying the value of prevention and showing the health and economic outcomes associated with the alternatives. The work helped to raise the billions of dollars needed to support polio eradication. The investments will prevent devastating cases of polio and realize an estimated $40-$50 billion in net benefits by the countries covered by the GPEI, while protecting the significantly larger net benefits enjoyed by the countries that stopped wild poliovirus transmission without support of the GPEI.

In 1988, the World Health Assembly resolved to eradicate polio worldwide. Since then, four of the six World Health Organization (WHO) regions have been certified as polio-free: the Americas in 1994, the Western Pacific Region in 2000, the European Region in 2002, and the South-East Asia Region in 2014. Currently, nearly 80% of the world's population lives in areas certified as polio-free. Certification may be considered when ≥3 years have passed since the last isolation of wild poliovirus (WPV) in the presence of sensitive, certification-standard surveillance. Although regional eradication has been validated in the European Region and the Western Pacific Region, outbreaks resulting from WPV type 1 (WPV1) imported from known endemic areas were detected and controlled in these regions in 2010 and 2011, respectively. The last reported case associated with WPV type 2 (WPV2) was in India in 1999, marking global interruption of WPV2 transmission. The completion of polio eradication was declared a programmatic emergency for public health in 2012, and the international spread of WPV1 was declared a public health emergency of international concern in May 2014. The efforts needed to interrupt all indigenous WPV1 transmission are now being focused on the remaining endemic countries: Nigeria, Afghanistan, and Pakistan. WPV type 3 (WPV3) has not been detected in circulation since November 11, 2012. This report summarizes the evidence of possible global interruption of transmission of WPV3, based on surveillance for acute flaccid paralysis (AFP) and environmental surveillance.

In 1988, the World Health Assembly resolved to interrupt wild poliovirus (WPV) transmission worldwide. By 2006, the annual number of WPV cases had decreased by more than 99%, and only four remaining countries had never interrupted WPV transmission: Afghanistan, India, Nigeria, and Pakistan. The last confirmed WPV case in India occurred in January 2011, leading the World Health Organization (WHO) South-East Asia Regional Commission for the Certification of Polio Eradication (SEA-RCC) in March 2014 to declare the 11-country South-East Asia Region (SEAR), which includes India, to be free from circulating indigenous WPV. SEAR became the fourth region among WHO's six regions to be certified as having interrupted all indigenous WPV circulation; the Region of the Americas was declared polio-free in 1994, the Western Pacific Region in 2000, and the European Region in 2002. Approximately 80% of the world's population now lives in countries of WHO regions that have been certified polio-free. This report summarizes steps taken to certify polio eradication in SEAR and outlines eradication activities and lessons learned in India, the largest member state in the region and the one for which eradication was the most difficult.

When this journal last published a special supplement on polio nearly 18 years ago, we lived in a world that was still deeply entangled with this devastating virus [1]. All 3 poliovirus serotypes were still circulating on four continents. Some of the world’s largest countries remained mired in the disease, some with thousands of cases each year. Most tellingly, a number of polio-infected countries, particularly in Africa, had not even introduced core eradication strategies, such as polio national immunization days (NIDs). Both financial and human resources were stretched; worldwide, <250 people were employed full time in a program whose success would eventually require, at its peak, reaching and vaccinating >600 million children multiple times per year. | Despite these realities, optimism and enthusiasm were running high in 1997. Nelson Mandela himself had, just the previous year, launched the continent-wide Polio-Free Africa initiative accompanied by a Kick Polio Out of Africa social mobilization campaign. The massive Operation MECACAR was rapidly clearing virus from the 18 participating countries, spanning 2 continents and coordinating and collaborating through shared poliovirus surveillance, cross-border planning, and synchronized NIDs across the Middle East, Caucasus, Central Asian Republics, and Russian Federation. And in most of the world where the 4 core eradication strategies had been introduced, the number of both cases of polio-paralyzed children and polio-infected countries were falling rapidly (Figure 1). The sense that, with further program expansion, eradication might soon be inevitable was reinforced in 1999 by the eradication of the type 2 wild poliovirus serotype globally; that the last type 2 case was reported from Aligarh, India, suggested that eradication of the other serotypes would follow quickly, both in that country and globally. By 2000, 3 of the 6 regions of the World Health Organization (WHO) had seen their last indigenous poliovirus and were either already certified as polio free or soon would be. Although it was apparent that the original goal of completing wild poliovirus eradication globally by 2000 would be missed, the then Secretary-General of the United Nations, Mr Kofi Annan, convened a special Polio Eradication Summit in September of that year to ensure that the program remained on track for its secondary target of certification of global eradication in 2005. By 2001, polio had been reduced to 475 cases in 10 polio-endemic countries, compared with 350 000 cases in 125 polio-endemic countries in 1988.

BACKGROUND: In 2009, enhanced poliovirus surveillance was established in polio-endemic areas of Uttar Pradesh and Bihar, India, to assess poliovirus infection in older individuals. METHODS: In Uttar Pradesh, stool specimens from asymptomatic household and neighborhood contacts of patients with laboratory-confirmed polio were tested for polioviruses. In Bihar, in community-based surveillance, children and adults from 250 randomly selected households in the Kosi River area provided stool and pharyngeal swab samples that were tested for polioviruses. A descriptive analysis of surveillance data was performed. RESULTS: In Uttar Pradesh, 89 of 1842 healthy contacts of case patients with polio (4.8%) were shedding wild poliovirus (WPV); 54 of 85 (63.5%) were ≥5 years of age. Shedding was significantly higher in index households than in neighborhood households (P < .05). In Bihar, 11 of 451 healthy persons (2.4%) were shedding WPV in their stool; 6 of 11 (54.5%) were ≥5 years of age. Mean viral titer was similar in older and younger children. CONCLUSIONS: A high proportion of persons ≥5 years of age were asymptomatically shedding polioviruses. These findings provide indirect evidence that older individuals could have contributed to community transmission of WPV in India. Polio vaccination campaigns generally target children <5 years of age. Expanding this target age group in polio-endemic areas could accelerate polio eradication.

The world is on the verge of achieving global polio eradication. During >25 years of operations, the Global Polio Eradication Initiative (GPEI) has mobilized and trained millions of volunteers, social mobilizers, and health workers; accessed households untouched by other health initiatives; mapped and brought health interventions to chronically neglected and underserved communities; and established a standardized, real-time global surveillance and response capacity. It is important to document the lessons learned from polio eradication, especially because it is one of the largest ever global health initiatives. The health community has an obligation to ensure that these lessons and the knowledge generated are shared and contribute to real, sustained changes in our approach to global health. We have summarized what we believe are 10 leading lessons learned from the polio eradication initiative. We have the opportunity and obligation to build a better future by applying the lessons learned from GPEI and its infrastructure and unique functions to other global health priorities and initiatives. In so doing, we can extend the global public good gained by ending for all time one of the world's most devastating diseases by also ensuring that these investments provide public health dividends and benefits for years to come.