For the Record: A History of Polio Eradication Efforts
Gregory L. Armstrong, MD
Before licensing of the inactivated (1955) and live attenuated (1961) polio vaccines, poliomyelitis was ubiquitous and distributed globally. Poliovirus infected most people in childhood, causing paralysis in approximately 1 in 200. Where vaccine was introduced, it had a rapid effect on the disease. In the United States, reported paralytic cases fell from approximately 20,000 per year in the early 1950s to 2,525 in 1960 and 61 in 1965.
By the early 1980s, the feasibility of globally eradicating polio was already being discussed. Several characteristics of poliovirus made it an ideal candidate for eradication, including the lack of an animal reservoir and the availability of an effective, inexpensive, easily administered oral polio vaccine (OPV). Furthermore, experience in Cuba and Brazil had demonstrated the ability of mass vaccination campaigns to interrupt poliovirus transmission. In 1988, the World Health Assembly formally resolved to eradicate poliomyelitis by 2000, giving birth to the Global Polio Eradication Initiative (GPEI).
Much progress toward eradication was achieved in the 1990s: the number of cases globally dropped by >99%, polio was eliminated from the Americas, and 1 of the 3 types of wild poliovirus (type 2) was eradicated globally. However, the goal of eradication by 2000 was not achieved, and the program entered into a decade-long period where progress appeared to have stalled, with 1,000–2,000 cases annually. Critics began to question whether polio eradication was feasible or even ethical. However, during this period there was another trend in the program—one of determined innovation. In India, for example, where nothing seemed to be successful at bringing down case counts, the program underwent a major transformation, with innovations to improve supervision and accountability in the field and other innovations to identify and reach chronically undervaccinated groups—groups that were often outside the reach of the formal public health system. In addition, technical advances were brought to fruition, most importantly the division of OPV into its individual components ([monovalent] mOPV1 and mOPV3) for the first time since they had been combined into the trivalent vaccine in the 1960s. These monovalent vaccines and, later on, the bivalent (types 1 and 3) vaccine greatly increased immunogenicity because interference by the more robust type 2 component was removed.
In late 2011, the program found itself at a crossroads. It was becoming increasingly likely that transmission had been interrupted in India in early 2011, with the last reported case in January. This success seemed to answer the question of feasibility—if polio could be eradicated in India, it could be eradicated anywhere. However, in the 3 remaining “endemic” countries—Nigeria, Pakistan, and Afghanistan, where wild poliovirus transmission had never been interrupted—case counts were increasing, and multiple outbreaks were occurring in countries that had previously been polio free. In October 2011, GPEI’s independent monitoring board issued a critical report, stating bluntly that the program was “not on track to interrupt polio transmission” and that “polio eradication needs to be treated as a global health emergency” if the ultimate goal of the program was ever to be achieved. This report initiated a new era in the program, one in which the GPEI partnership has scaled up activities, particularly in the 3 remaining endemic countries, in order to complete eradication.
The strategy of wild poliovirus eradication is organized around 4 “pillars”:
Strengthening routine immunization programs
“Supplementary immunization activities” (SIAs) in the form of mass vaccination campaigns, either at the national or subnational level
Surveillance for acute flaccid paralysis (AFP) and confirmation of polio by laboratory testing of stool samples
Targeted “mop-up” campaigns around any confirmed cases of polio
In endemic countries and other countries with active wild poliovirus transmission, SIAs, the most visible aspect of the program, are typically conducted every 4–8 weeks until transmission has been stopped. AFP surveillance is a critical component in countries both with and without polio, where the surveillance system is expected to detect nonpolio cases of AFP at a rate of at least 1 per 100,000 per year in industrialized countries and 2 per 100,000 per year in developing countries. Environmental surveillance—the testing of sewage for polioviruses—is also a sensitive tool for poliovirus detection and plays an increasing role in surveillance for poliovirus.
The polio eradication program will not end with the last case of polio. In addition to interrupting wild poliovirus, the program will also need to interrupt circulation of vaccine-derived polioviruses (VDPVs). These viruses emerge usually from the type 2 component of OPV in locations where childhood vaccination coverage is exceptionally low and are eliminated by increasing vaccination coverage or conducting SIAs with the trivalent vaccine. To prevent further VDPV2 emergence, inactivated poliovirus vaccine is being introduced in countries where it is not in use, and trivalent OPV is being replaced with bivalent OPV. At the same time, GPEI will gradually transition its resources toward supporting other public health objectives (“legacy”), and laboratories with samples containing poliovirus will need to destroy or consolidate and safely store those samples (“containment”). The plan for carrying out this massive set of tasks is documented in the GPEI Polio Eradication and Endgame Strategic Plan, 2013–2018.
Dowdle WR, Cochi SL. Global eradication of poliovirus: history and rationale. In: Selmer BL, Wimmer E, editors. Molecular Biology of Picornaviruses. Washington, DC: ASM Press; 2002. p. 473–80.
Perspectives sections are written as editorial discussions aiming to add depth and clinical perspective to the official recommendations contained in the book. The views and opinions expressed in this section are those of the author and do not necessarily represent the official position of CDC.