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Am J Public Health. 2005 May; 95(5): 773–777.
PMCID: PMC1449254

Can We Capitalize on the Virtues of Vaccines? Insights from the Polio Eradication Initiative


Twenty-five years after the eradication of smallpox, the ongoing effort to eradicate poliomyelitis has grown into the largest international health initiative ever undertaken.

By 2004, however, the polio eradication effort was threatened by a challenge regularly faced by public health policymakers everywhere—misperception about the benefits and risks of vaccines. The propagation of false rumors about oral poliovirus vaccine safety led to the reinfection of 13 previously polio-free countries and the largest polio epidemic in Africa in recent years.

With deft management of such challenges by local, national, and international health authorities, poliomyelitis, a disease that threatened children everywhere just 2 generations ago, could soon be relegated to history like smallpox before it.

DISEASE ERADICATION “attacks inequities and provides the ultimate in social justice and equity,” as by design the benefits should accrue to all peoples in perpetuity.1(p112) The only completed eradication initiative to date was based on the widespread application of a vaccine, and this demonstrates the rare potential of immunization as a public health tool.2 Although endemic polio has now been eliminated from all but 6 countries in the world,3 the ultimate success of this massive initiative is still threatened by the same challenge that faces public health policymakers everywhere—misperceptions held by government officials, health professionals, the media, and the general public about the benefits and risks of vaccines, both now and in the future.

We examine the progress that has been made toward the eradication of poliomyelitis and the prospects for its completion, including the eventual cessation of polio immunization, against a background of recent events, both local and international, that have influenced these prospects.


In 1988, the World Health Assembly adopted the goal of polio eradication by the year 2000.4 This World Health Assembly consensus was the result of a broad combination of influences ranging from the increasing evidence that human-to-human transmission of polioviruses could be interrupted to the ceaseless promotion of a global eradication target by many scientifically respected advocates.5 Most important, in the Americas polio was rapidly being eliminated through a 4-pronged strategy consisting of high routine immunization coverage with oral poliovirus vaccine (OPV); national immunization days targeting every child younger than 5 years for supplementary OPV doses; surveillance for, and laboratory investigation of, all cases of acute flaccid paralysis among children younger than 15 years; and massive, house-to-house “mop-up” campaigns to interrupt the final chains of transmission.6

Despite the global consensus to eradicate polio, the number of countries implementing the strategies initially grew very slowly because of limited promotion of the goal internationally, a lack of resources, and other health priorities both within and outside immunization programs.7 With the certification of polio eradication in the Americas in 19948 and the elimination of polio from China shortly thereafter, there was a rapid scale-up of the global effort, with striking examples of international cooperation. In April 1995, 18 countries of the Middle East, Caucasus, Central Asian Republics, and Russia launched Operation MECACAR, beginning a multiyear effort to immunize 85 million children against polio during synchronized national immunization days.9 In 1996, then-President Nelson Mandela of South Africa and 45 other heads of state from throughout Africa launched the Kick Polio Out of Africa campaign.10

As the result of these and similar collaborative efforts throughout the world,11 every country had introduced the key polio eradication strategies by 2000, including conflict-affected countries such as Afghanistan, the Democratic Republic of the Congo, and Somalia. Globally, an estimated 10 million health workers and volunteers immunized 600 million children in 100 countries during multiple rounds of national immunization days in that year.12 By that time, a truly global surveillance and laboratory network had been established, with district-level weekly or monthly reporting from every country in which polio was endemic or recently endemic. More than 60000 diagnostic specimens from more than 30000 acute flaccid paralysis patients were being analyzed in the network every year to identify the remaining chains of polio transmission and target supplementary immunization activities.13

These national efforts were supported by a robust partnership that was spearheaded by the World Health Organization, Rotary International, the US Centers for Disease Control and Prevention, and the United Nations Children’s Fund (UNICEF). The polio partnership grew to include national governments, foundations, international humanitarian organizations, national and international nongovernmental organizations, donor agencies, the private sector, and development banks. The most extraordinary partner was the international service organization Rotary, which in addition to countless hours donated by its 1.2 million volunteers in 140 countries, contributed over US$600 million to the global effort. By the end of 2003, more than US$3 billion in external financing and US$2.5 million in in-kind contributions had been expended to eradicate polio in the countries in which it was endemic.14 The capacity to mobilize resources on this scale for a single disease control effort was very much attributable to the concept of polio eradication as a global public good.15 That all children everywhere might benefit in perpetuity from this initiative proved a powerful investment incentive to a broad range of stakeholders from community leaders to national health policymakers to ministers of international development and even G8 leaders.16

By the end of 2003, this international eradication effort had eliminated polio from all but 6 countries in the world, demonstrating that with the proper application of the eradication strategies and international cooperation, poliovirus transmission could be rapidly interrupted anywhere (Figure 1 [triangle]). In the 6 remaining countries in which polio was endemic (Nigeria, India, Pakistan, Egypt, Afghanistan, and Niger), the disease was either highly localized or had been interrupted in large geographic areas, setting the stage for global eradication. Despite this extraordinary progress and massive international investment, in 2003 a series of misunderstandings and misrepresentations about the safety of OPV in 1 state of 1 country rapidly escalated, leading to the suspension of polio campaigns in that area, a nationwide epidemic, and the reinfection of many previously polio-free countries. For the first time in history, more countries suffered importations of polio than were actually endemic for the disease, putting the entire eradication initiative at risk.

Distribution of endemic poliomyelitis (dark gray) (a) in 1988, the year the World Health Assembly voted to eradicate the disease and at which time polio was present in more than 125 countries, and (b) at the end of 2003, when endemic polio was limited ...


This most recent and perhaps most insidious threat to the interruption of wild poliovirus transmission globally began in mid-2003, in the key state of Kano in northern Nigeria, when a small number of local opinion leaders began questioning the basis for the mass polio immunization campaigns. Some of these local leaders soon began voicing a wide range of theories about OPV itself, suggesting that it contained, among other things, HIV and antifertility agents.17 Within weeks, the local media were full of reports of conspiracy theories, the most popular being that the polio campaign was in fact an effort to depopulate the north of the country using “contaminated” OPV. Using the Internet for its research, several members of the local press soon found material to further sustain these theories, such as long-debunked theories linking OPV to the origins of HIV.18

By the end of August 2003, political leaders in Kano and adjoining states had decided to suspend the polio campaigns until the rumors could be addressed. Unfortunately, within months hundreds of children had been paralyzed in Nigeria as epidemic polio returned to the country. The virus rapidly spread from Kano to other states within Nigeria that had long been polio-free (e.g., the megacity of Lagos) as well as to other, polio-free, countries of sub-Saharan Africa (Figure 2 [triangle]) and beyond, costing over US$100 million in emergency response activities.19 One of Africa’s most impressive achievements in health and international cooperation was at risk, as well as the global eradication effort.

Reported polio cases in Africa (January 1, 2003, to July 31, 2004) and countries participating in synchronized outbreak response campaigns in late 2004.

Recognizing that a failure to implement the strategies in any remaining area in which polio was endemic would put the entire global eradication effort and investment at risk, on January 15, 2004, the leaders of the World Health Organization and UNICEF convened an emergency meeting of the health ministers of the 6 remaining polio-infected countries and 3 of the recently reinfected countries. The meeting also brought together political and health leaders from key states and provinces within those countries in which polio was endemic. After a day of deliberations, the ministers issued the Geneva Declaration on the Eradication of Poliomyelitis, stating that 2004 presented the best, and possibly last, chance to achieve this global public good.20 The declaration introduced an aggressive plan to immunize a total of 250 million children during up to 6 door-to-door polio immunization campaigns in each country within the next 12 months. The Nigerian minister outlined an extensive program of joint work with Kano state authorities to resolve the remaining doubts about the safety of the polio vaccine and then allow the resumption of the polio immunization campaigns.

As of January 18, 2005, the “intensified” effort in Asia was on track. After a marked increase in polio immunization campaign quantity and quality, poliovirus transmission in India, Pakistan, and Afghanistan was highly focal, with 182 cases reported for 2004 compared with 336 in 2003. In all 3 countries, large-scale mop-up activities had been added to the national program to interrupt transmission as rapidly as possible. Although there continued to be widespread low-level poliovirus transmission in Egypt, the quality of eradication activities in that country had also improved markedly since early 2004. In contrast, sub-Saharan Africa was still experiencing epidemic polio; cases in Nigeria and Niger had soared to 788 (vs 395 in 2003), and since January 2003, a total of 260 children had been paralyzed in 13 previously polio-free countries by polioviruses that were genetically linked to viruses that had originated in northern Nigeria. However, the health ministers of 23 west and central African countries had initiated a series of massive, synchronized campaigns for late 2004 and 2005, targeting 80 million children, to get that eradication effort back on track for an end-of-2005 target.21

The success of this intensified polio eradication effort now depends on (1) direct oversight by all political, traditional, religious, and community leaders in each area in which the disease is endemic to ensure that every child is reached during each immunization campaign, and (2) action by the international community to close rapidly the US $275 million funding gap for intensified eradication activities worldwide during 2005–2006.


Even before this new challenge to polio eradication appeared, 3 events had led some commentators to question whether the eventual cessation of polio immunization, an implicit goal of the eradication program, would ever be feasible, regardless of the success of the ongoing efforts to interrupt wild poliovirus transmission. First, through the application of new molecular tools, virologists demonstrated that a 1999–2000 polio outbreak in Hispaniola was not attributable to a wild poliovirus, but rather a circulating vaccine-derived poliovirus (cVDPV).22 Second, a team of virologists succeeded in synthesizing a viable poliovirus de novo from the genetic code, which was by then available on the Internet.23 Third, an individual with a primary immunodeficiency syndrome was found to have excreted a neurovirulent vaccine-derived poliovirus (iVDPV) for as long as 10 years.24

Although all these developments had for some time been deemed possible, these events began a new debate about the technical feasibility and wisdom of ever stopping immunization with OPV. This debate was further heightened by the events of, and subsequent to, September 11, 2001, most notably the use of biological agents for malicious purposes in the United States and the resumption of limited immunization with smallpox vaccine.25 Some argued that given the challenges of ensuring the safe containment of laboratory stocks of wild polioviruses in a post–September 11 world, and establishing and maintaining a vaccine stockpile of sufficient size to respond to future outbreaks, it would be necessary to continue polio immunization indefinitely.26 One commentator suggested that although the inactivated poliovirus vaccine (IPV) could provide population immunity while avoiding the risks of OPV, the much higher price of IPV made continued OPV a more appropriate strategy for developing countries.27

The potential “prisoners’ dilemma” that was emerging, in which the continued use of OPV after eradication of wild-type polioviruses might lead to the emergence of new virulent vaccine-derived strains, required acceleration of the ongoing research program to define the magnitude of these risks and potential strategies for dealing with them (Table 1 [triangle]). More than 7000 Sabin-derived polioviruses were screened to search for cVDPVs, and collaborative studies were established with clinics that treated individuals with primary immunodeficiencies. Within 2 years, a substantial body of data demonstrated that cVDPVs and iVDPVs were in fact rare and posed decreasing risks with time after OPV cessation.28 All 4 cVDPV outbreaks had been rapidly controlled with mass OPV campaigns. Of the 19 iVDPVs identified to date worldwide, only 2 of the original hosts are still known to be excreting virus, with no evidence of secondary transmission. In addition, by the end of 2003, 157 countries had initiated the necessary nationwide survey of facilities for stocks of wild and vaccine-derived polioviruses and potentially infectious materials, and 81 countries, including the United States, had completed inventories.29

Risk Estimates of Paralytic Disease Owing to Polioviruses After Interruption of Wild Poliovirus Transmission Globallya

In September 2003, a World Health Organization–convened meeting of international experts concluded that the continued use of OPV after eradication of wild-type polioviruses, in an environment of decreasing OPV coverage because of the cessation of polio campaigns, posed a medium- to long-term risk to the international goal of eliminating paralytic poliomyelitis caused by circulating polioviruses.30 The group stated that OPV immunization should be stopped as soon as possible after interruption of wild poliovirus transmission, while high population immunity and surveillance sensitivity could reduce the risk of cVDPV emergence and facilitate the prompt detection and response to such events if they occurred. Recognizing that IPV will not substantially change the future risk of polio in many countries, particularly those with low routine immunization coverage, the World Health Organization is providing countries with the evidence needed to make their own risk analysis on the costs and benefits of IPV for routine childhood immunization after OPV cessation. In addition to providing guidance on IPV policy, the World Health Organization is giving particular attention to helping individual countries establish and maintain the surveillance and response capacity needed before, during, and after OPV immunization cessation.31 This work includes the development of stockpiles of monovalent OPV, to allow type-specific responses to future polio outbreaks, and, potentially, Sabin-based IPV to limit a proliferation in the number of facilities undertaking large-scale amplification of wild poliovirus strains after the cessation of OPV immunization. The ultimate success of this strategy will depend on (1) negotiating international concurrence to stop OPV use in all countries over a very short time period (to avoid the risk of exposing other areas to vaccine-derived strains, particularly those that choose not to introduce IPV), and (2) establishing and maintaining an international stockpile of poliovaccines to manage the cVPDVs that might emerge during the cessation of OPV immunization.


Since its launch in 1988, the Global Polio Eradication Initiative has grown into the largest international health effort ever, generating broad international collaboration and community participation. In 2004, the initiative was intensified to interrupt polio transmission in the 6 remaining countries in which polio was endemic and, eventually stop the routine use of OPV. The greatest recent challenge to interrupting polio transmission has been the promotion of false rumors about OPV safety in 1 state of 1 country. Ironically, the greatest challenge to the cessation of OPV immunization in the future may be establishing international consensus on the real risks of that vaccine once wild poliovirus transmission has been interrupted. With deft management of these challenges by local, national, and international health policymakers, poliomyelitis, a disease that threatened children everywhere just 2 generations ago, could soon be relegated to history like smallpox before it.


The authors thank Dr Daniel Tarantola for his extensive and valuable comments during the preparation and revision of this article.


Peer Reviewed

The authors originated and developed this article jointly. R.B. Aylward wrote the initial draft, incorporating the comments of D.L. Heymann, and finalized the article on receipt of the reviewer comments.


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