A History of Polio Eradication Efforts
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. The last cases of naturally occurring paralytic polio in the United States were in 1979, when an outbreak occurred among the Amish in several Midwestern states.
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).
The strategy of wild poliovirus (WPV) eradication was organized around 4 “pillars”:
- Strengthening routine immunization service delivery to achieve high infant vaccination coverage with OPV.
- Conducting supplementary immunization activities (SIAs) in the form of mass vaccination campaigns for children, either at the national or subnational level. In polio-endemic countries and other countries with active WPV transmission, SIAs are typically conducted every 4–8 weeks until transmission has been stopped.
- Surveillance for acute flaccid paralysis (AFP) and confirmation of polio by laboratory testing of stool samples. 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 important role in poliovirus surveillance.
- Conducting targeted “mop-up” vaccination campaigns in a focal geographic area around any confirmed polio cases.
The GPEI made rapid early progress, with a reduction in the number of polio-endemic countries from 125 countries in 1988 to 10 in 2001, polio-free certification in the Americas Region (1994), Western Pacific Region (2000), and European Region (2002) and eradication of WPV type 2 in 1999. However, the goal of eradication by 2000 was not achieved, and progress stagnated during the next decade due to major programmatic challenges including conflict, political instability, hard-to-reach populations, and poor infrastructure. Determined programmatic innovation was needed to overcome these challenges. In India, for example, a series of operational innovations were developed and implemented to improve vaccination service delivery and reach chronically undervaccinated groups—groups that were often outside the reach of the formal health care delivery system. In addition, vaccine innovations were brought to fruition, most importantly the division of OPV into monovalent components (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.
By 2011, the GPEI was at a crossroads. The last WPV case in India was reported in early 2011. This success answered the question of feasibility—if polio could be eradicated in India, it could be eradicated anywhere. However, in the 3 remaining countries where endemic wild poliovirus transmission had never been interrupted—Nigeria, Pakistan, and Afghanistan—case counts were increasing, and poliovirus importations from the polio-endemic countries caused multiple outbreaks in many 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 poliovirus 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 led to the World Health Assembly declaring global polio eradication “a programmatic emergency for global public health” in 2012. In addition, the World Health Organization declared the international spread of WPV to previously polio-free countries to be “a public health emergency of international concern” in 2014, triggering oversight by an emergency committee under the International Health Regulations.
The World Health Assembly declaration of polio eradication as a public health emergency in 2012 initiated a new era in which emergency operations were established in GPEI partner agencies and at national and subnational levels in the last remaining polio-endemic countries of Nigeria, Pakistan, and Afghanistan to complete eradication. Substantial progress has been achieved with the renewed efforts. WPV type 3 was last detected in 2012, and polio-free certification in the Southeast Asia Region was announced in 2014. Four WPV cases were reported in Nigeria in August 2016; these are the first cases reported in the country since July 2014. No WPV cases have been detected elsewhere in Africa since August 2014. As of September 14, 2016, Afghanistan, Pakistan, and Nigeria were the last three countries with endemic WPV type 1 transmission, and 26 cases had been reported worldwide in 2016.
In May 2013, the 66th World Health Assembly endorsed the Polio Eradication and Endgame Strategic Plan 2013–2018. This plan provides a timeline for completion of polio eradication by eliminating all paralytic polio due to both WPV and vaccine-derived polioviruses (VDPVs). VDPVs are very rare strains of poliovirus, genetically changed by mutations from the original strain contained in OPV, which can emerge in locations where childhood vaccination coverage is low. To prevent type 2 VDPV emergence, which accounted for 79% of the circulating VDPVs in 2014–2015, a coordinated global switch in all countries from use of trivalent (types 1, 2 and 3) OPV to bivalent OPV (types 1 and 3) was implemented in April 2016. To mitigate risks by increasing population immunity to poliovirus type 2, inactivated poliovirus vaccine (IPV) is being introduced in all countries where it has not been in use. The plan also has an objective to contain poliovirus and certify interruption of poliovirus transmission. In order to contain poliovirus, laboratories with samples containing poliovirus will need to destroy or consolidate and safely store those samples. Requirements for certifying a WHO region as free of WPV include the absence of any WPV for a minimum of 3 years in all countries of the region and the presence of certification-standard surveillance in all countries during that 3-year period. Planning is also underway to prepare for the period after polio eradication is certified, so that polio eradication assets in high priority countries can be leveraged and transitioned to improve global health as part of polio eradication’s legacy.
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Eric E. Mast, Stephen L. Cochi