In recent decades, numerous factors—including social, political, economic, and environmental factors—have influenced global perspectives on the practicality, desirability, and approaches of eradication initiatives. Two global eradication efforts, the Smallpox Eradication Program (SEP) and the Global Polio Eradication Initiative (GPEI), offer important lessons on implementation strategies for addressing challenging factors to global eradication and other global health intiatives. This paper will explore how SEP and GPEI have utilized implementation strategies to further their eradication goals, and how some of these implementation strategies have evolved over time.
The successes and learnings from the Smallpox Eradication Program (SEP), the Expanded Program on Immunization (EPI) and initial polio eradication efforts in the Philippines, Brazil, and Cuba garnered optimism and focused efforts from Rotary International and the Pan-American Health Organization (PAHO) to prioritize polio eradication efforts [1, 2]. In 1981, PAHO concluded the elimination of polio was feasible, and with the support of the United Nations International Children’s Emergency Fund (UNICEF), launched an initiative to eradicate polio from the Americas in 1985 [2, 3]. Realizing the complexity and spread of the disease, the World Health Assembly subsequently launched the Global Polio Eradication Initiative (GPEI) in 1988 . PAHO effectively eliminated polio in the Americas by 1994, and was the first WHO region to do so,  while other WHO regions then grew motivated and followed suit. The global effort has since lowered the incidence of polio by over 99% .
The SEP, launched in 1959 by the World Health Organization (WHO), faced resource limitations and lack of commitment from countries early on and had not achieved much progress towards elimination in Africa, Asia, or South America by 1966 [7,8,9,10]. In 1967, a re-vamped Intensified Eradication Program was initiated, which included an expansion of vaccine manufacturing capacity in endemic countries and a heightened focus on developing disease surveillance systems in countries where eradication activities were being implemented, in addition to the ongoing mass vaccination campaign strategy [11, 12]. At the same time, the development of the bifurcated needle improved the effectiveness of vaccine delivery and key strategies including efforts to achieve universal vaccination, surveillance-containment approaches where known or suspected contacts were rapidly identified and isolated, case identification, quarantine, contact tracing, primary vaccination, and ring vaccination strategies were deployed [9, 13,14,15,16]. By the mid-1970s, final cases were detected and efforts to certify the world free of smallpox were underway. On May 8, 1980 the 33rd World Health Assembly officially declared the world free from smallpox, a momentous achievement for global public health [8, 14].
The SEP demonstrated the promise of health programs targeting vaccine-preventable diseases to dramatically reduce the burden of communicable diseases globally, but the SEP experience also brought to light serious health system inadequacies which needed to be addressed for immunizations to be delivered at scale . Recognizing this, in the final years of the SEP, the World Health Organization launched the EPI in 1974 . The EPI prioritized immunization against other diseases such as diphtheria, measles, and polio, gradually shifting focus from the campaign-based strategy of the SEP to delivery through routine services. Inadequate equipment, lack of governmental and public awareness, and insufficient monitoring systems continued to challenge the EPI program; still, the EPI progressed, including greater emphasis on providing immunizations for diseases, through routine health services and increasing coverage of a package of vaccines to larger proportions of children [9, 17]. More resources were needed for this program, and WHO and UNICEF both provided substantial investments, under the leadership of WHO Director General, Halfdan Mahler, in 1977, and UNICEF’s executive director, James Grant, shortly thereafter [16, 18].
Of the vaccine-preventable diseases, polio attracted much attention given the debilitating nature of the illness among children and had champions spearheading efforts to eliminate poliovirus from the United States, which was achieved in 1979 . Given the initial successes in reducing the burden of polio in the United States and Europe between 1955 (introduction of IPV in the US) and 1960s  through routine immunization was not successfully replicated in the lower-resource countries, Sabin recommended using mass immunizations to supplement routine immunizations . The approach, first adopted by Cuba on national scale  and in pilots in Brazil in the 1960s and later nationally in the 1980s  along with other countries in the Americas culminated in PAHO setting forth a goal to eliminate polio across the Americas by 1990 . PAHO countries strengthened their laboratory networks and, perfected the concept of mass immunization campaigns called “national immunization days” (NIDs) starting in Brazil in 1980 and subsequently adopted as PAHO’s model for eradication in the Americas . Intercountry cooperation also played a key role in PAHO’s success by synchronizing efforts and bolstering shared motivation towards the common goal of eliminating poliovirus from the region .
Given PAHO’s success as well as advocacy efforts led largely by Rotary International, the World Health Assembly passed a resolution in 1988 to globally eradicate polio by the year 2000 and launched the Global Polio Eradication Initiative (GPEI) [4, 24]. Core partners of the GPEI included the World Health Organization (WHO), the US Centers for Disease Control and Prevention (CDC), Rotary International, and the United Nations Children’s Fund (UNICEF) at inception, and were later joined by the Bill and Melinda Gates Foundation (BMGF) in 2000, and Gavi, The Vaccine Alliance, in 2019. The partners have worked with governments and other implementers in more than 200 countries and territories to vaccinate over 2.5 billion children globally since 1988.(8) Although the eradication goal set for 2000 has not been achieved, the GPEI has made remarkable progress in reducing the global incidence of polio by over 99% as of early 2020 [6, 24].
The GPEI was established with a four-pronged eradication approach which was developed in the PAHO region as part of its regional effort to eradicate polio, and which drew upon tactics utilized in both the SEP and EPI. These prongs included: surveillance, routine immunization, supplementary immunization activities (SIAs), and targeted mop-up campaigns for reaching high-risk populations. Importantly, when the GPEI drafted it’s an initial strategic plan it was felt by partners the “specialized effort” required for eradication could be used as “leading edges” for strengthening routine immunization and primary health care more broadly . This reflected the PAHO experience in which routine immunization served as the backbone of the eradication effort, as well as the relative success of the EPI in the preceding years to expand immunization coverage (at the time, the EPI was targeting 80% DTP3 coverage globally) . While this four-pronged strategy has remained over the course of the GPEI, the balance of these strategies and the implementation mechanisms required to achieve each have necessarily shifted, expanded, and increased in precision over time. These adaptations have been in response to emerging implementation challenges – some of which are specific to the complexities of eradicating wild poliovirus – but also reflect key operational lessons learned over the course of the SEP, EPI, and early polio programs. These include the need for setting measurable objectives, evaluating progress, establishing quality control mechanisms for vaccines, ensuring highly qualified staff, and maintaining an active research agenda to inform implementation and provide evidence to solve outstanding questions .
As part of the Synthesis and Translation of Research and Innovations from Polio Eradication (STRIPE) consortium convened by The Johns Hopkins School of Public Health with partners from seven selected countries (Afghanistan, Bangladesh, Democratic Republic of the Congo, Ethiopia, India, Indonesia, and Nigeria), we implemented a multi-pronged scoping review to explore how global eradication strategies evolved from the SEP to the GPEI. To ensure representativeness, the countries were selected to represent the different epidemiological classifications for polio (endemic, outbreak, at-risk and polio-free), different geographical regions for the GPEI program, country income classifications, conflict-affected compared to stable countries, and countries that are regional leaders and representing large population. Our aim was to understand why some strategies were readily translated and others were not, and the role that people, context, and time played in such translation, or lack thereof. We hope to draw lessons for future global eradication programs and other efforts to respond to disease emergencies and widespread epidemics, and strengthen health systems globally.
While there have been other initiatives to document the histories of the smallpox and polio eradication programs, [13, 23, 28,29,30,31,32,33,34,35,36,37,38] our focus is to apply an implementation science lens to explore in detail how both the SEP and the GPEI utilized specific strategies to implement their programs. By considering the actors, processes, and contexts for conducting program activities, and how interactions between these forces contribute to program successes or failures, this study contributes a new perspective on these eradication initiatives. This holistic approach can help to synthesize and understand the contributors and barriers to program success and facilitate the application of relevant lessons to other eradication initiatives, broader public health programs, and across multiple disciplines to improve program design and implementation, ultimately contributing to better population health [39,40,41]. Accordingly, in this review study we have drawn upon concepts, theories, and frameworks from the interdisciplinary field of implementation science to understand the strategies, outcomes, tools, and principles/recommendations across the span of smallpox and polio eradication activities. Specifically, we reviewed implementation strategies documented from the SEP and the strategies and experiences under the GPEI using a standardized set of implementation science strategies from the Expert Recommendations for Implementing Change (ERIC) project , implementation outcomes , contextual factors from the Consolidated Framework for Implementation Research (CFIR) , and a recent review that defined different global health knowledge areas .