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Progress Toward Global Eradication of Poliomyelitis, 2002
Since the 1988 World Health Assembly resolution to eradicate poliomyelitis globally (1) through 2002, the number of countries where polio is endemic declined from 125 to seven, and the estimated incidence of polio decreased >99% (2). In 2002, the European Region became the third World Health Organization (WHO) region certified as polio-free, joining the Region of the Americas and the Western Pacific Region, certified polio-free in 1994 and 2000, respectively (3--5). Despite these achievements, a provisional total of 1,920 polio cases were reported during 2002, a substantial increase from 483 in 2001, reflecting primarily the large polio epidemic in India (6). This report summarizes global progress achieved in polio eradication during 2002 and describes remaining challenges.
Implementation of Polio Eradication Strategies
Coverage among infants with 3 doses of oral poliovirus vaccine (OPV3) in 2001 was estimated at 75% globally, a decrease from 82% in 2000.* Coverage varied among WHO regions, from 54% in the African Region to 95% in the European Region. Except for Egypt, reported routine vaccination coverage in 2002 continues to be low in the remaining countries where polio is endemic.
All countries where polio is endemic and many countries where polio was recently endemic conducted supplemental immunization activities (SIAs) during 2002. An estimated 500 million children were vaccinated during 266 rounds of National Immunization Days (NIDs), sub-NIDs (SNIDs)§, or mopping-up activities. All countries used house-to-house vaccination in part or all of the SIA target areas. SIA monitoring data confirmed low vaccination coverage for some SIAs, particularly in Uttar Pradesh (India) and northern Nigeria, where poliovirus transmission remained intense.
All WHO regions have achieved certification-standard acute flaccid paralysis (AFP) surveillance consisting of 1) an annual nonpolio AFP detection rate of >1 per 100,000 persons aged <15 years and 2) at least two adequate stool specimens¶ collected from >80% of persons with AFP (Table). The African Region reached certification-standard AFP surveillance quality for the first time in 2002, with a nonpolio AFP detection rate of 3.1 and adequate specimens collected from 81% of persons with AFP. Globally, the nonpolio AFP rate increased from 1.6 in 2001 to 1.9 in 2002. The proportion of persons with AFP from whom adequate stool specimens were collected increased from 82% in 2001 to 87% in 2002. Except for Somalia (adequate specimens from 67% of persons with AFP), all other countries where polio is endemic achieved certification-standard AFP surveillance in 2002.
In 2002, a total of 97% of the 145 poliovirus laboratories in the global network were formally accredited by WHO. Global network laboratories tested approximately 70,000 fecal samples, a 12% increase over 2001. Despite a fourfold increase in the isolation of wild virus from 2001 to 2002 (Table), timeliness of reporting of laboratory results improved. Primary isolation results were available within 28 days of receipt in the national laboratory for 90% of samples, and intratypic differentiation was available within 28 days of isolate receipt in the regional reference laboratory for 88% of isolates.
Impact on Wild Poliovirus Transmission
The number of countries where polio is endemic decreased from 10 in 2001 to seven in 2002. Of the 1,920 polio cases reported in 2002, a total of 1,893 (99%) were reported from three countries: India (1,599), Nigeria (201), and Pakistan (93) (Figure). Despite certification-standard surveillance, few cases were reported in Afghanistan (11), Egypt (seven), Niger (three), and Somalia (three). Virus importations were detected in Zambia (two cases) and Burkina Faso (one case). Recently endemic poliovirus reservoir (Ethiopia, Angola, and Sudan) reported no cases in 2002 in the presence of sensitive surveillance.
A substantial increase in polio occurred in India, from 268 cases reported in 2001 to 1,599 cases in 2002, representing >83% of the globally reported cases in 2002. The states of Uttar Pradesh and Bihar accounted for 1,241 (78%) and 121 (8%) of the total cases in India, respectively. During 2001--2002, the number of genetic lineages of wild poliovirus circulating in India remained the same for wild poliovirus type 1 (P1) (three major lineages) and wild poliovirus type 3 (P3) (four major lineages). Analysis of genetic data demonstrated that all lineages identified in India in 2002 were derived from strains that circulated in Utter Pradesh during 2000--2001.
In Nigeria, the increased number of reported wild poliovirus cases was in part caused by improved AFP surveillance. Despite the increase, poliovirus circulation was restricted geographically, with seven states in northern Nigeria reporting >80% of cases; southern Nigeria remained largely poliovirus-free. Pakistan reported 22% fewer cases in 2002 (93) compared with 2001 (119). In addition, transmission was more focal in 2002 compared with 2001. Genetically related P3 clusters decreased from six in 2001 to one in 2002.
Egypt continued to report P1 in 2002. Since 2000, environmental surveillance has detected evidence of widespread P1 transmission in Upper and Lower Egypt, compared with AFP surveillance, which detected few poliovirus-confirmed cases. During the second half of 2002, seven cases of polio were detected from Upper and Lower Egypt, including the greater Cairo area.
In Somalia, the last polio case was reported in October 2002 and was caused by P3. Only eleven poliovirus-confirmed cases were reported in 2002 in Afghanistan, despite the recent war and return of approximately 2 million refugees. Genetic sequencing data indicate that the only remaining area of endemic transmission in Afghanistan is in the south, near Kandahar. Low-intensity poliovirus transmission continued in Niger in 2002. Although polioviruses detected are related closely to Nigerian polioviruses, evidence exists of independent low-level wild poliovirus transmission in southern Niger. Vaccination campaigns were conducted in response to virus importations into Burkina Faso and Zambia with no subsequent spread.
Following episodes of circulating vaccine-derived poliovirus (cVDPV) type 1 in Haiti, the Dominican Republic (2000--2001), and the Philippines (2001), another outbreak (four cases) of cVDPV type 2 was detected during March--April 2002 in Madagascar, a country where OPV3 coverage in 2000 was 34% (7,8). No additional cases were detected in Madagascar after NIDs were conducted in mid-2002. The global polio laboratory network continues to screen for cVDPV isolates. Regional reference laboratories immediately refer suspected isolates to specialized laboratories for genetic sequencing studies. Since 2000, approximately 3,400 Sabin viruses from AFP cases have been screened without finding additional cVDPVs.
Preparations for Post-Eradication Activities
Progress has been made toward laboratory containment of wild polioviruses (9). Of 207 countries and territories where polio is not endemic, 155 (75%) have established a national task force and a national plan of action for laboratory containment. By the end of 2002, a total of 149 WHO member states had initiated national laboratory surveys. Of those, 79 countries had completed and submitted an inventory of facilities holding wild-type polioviruses and potentially infectious materials, including 41 of 51 European, 33 of 36 Western Pacific, and five of 23 Eastern Mediterranean countries. Laboratory surveys are ongoing in 19 of 48 countries in the Region of the Americas, including the United States.
As part of post-eradication polio vaccination policy development, a framework was created for assessing and managing the risks for polio in the post-eradication era and addresses risks associated with 1) polio from continued use of OPV (i.e., vaccine-associated paralytic polio), 2) cVDPV or vaccine-derived poliovirus associated with immunodeficiency, and 3) the handling of wild poliovirus stocks. The framework summarizes knowledge on the magnitude of these risks and their expected evolution over time.
Reported by: Vaccines and Biologicals Dept, World Health Organization, Geneva, Switzerland. Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Global Immunization Div, National Immunization Program, CDC.
Progress toward global polio eradication in 2002 included the certification of eradication in 51 countries of the European Region, a decrease from 10 remaining countries in 2001 to seven countries in 2002, and continued absence of indigenous wild poliovirus type 2, last detected in October 1999 (10). Approximately 3 billion persons now live in 134 countries, areas, and territories certified free of indigenous wild poliovirus.
Further progress was evident in the reduction in diversity of poliovirus lineages in the majority of countries, and polio-free status was sustained in recently endemic, challenging country settings such as Bangladesh, the Democratic Republic of Congo, Ethiopia, and Sudan. In Angola, the April 2002 cease fire resulted in vaccinators having access to children in areas that had been inaccessible for years. Access to children also improved in Somalia in 2002. In addition, Afghanistan has recovered from a disruption in AFP surveillance activities following the September 11, 2001, terrorist attacks in the United States.
Despite these achievements, the fourfold increase in polio incidence globally, focused in India and northern Nigeria, represents a critical challenge to the program. Efforts are being focused on the northern Indian states of Uttar Pradesh and Bihar because of the intensity of transmission, and genetic evidence that these states were the source for re-introduction of poliovirus into other states that had become polio-free. Key factors contributing to the epidemic include the decline in the number, extent, and quality of SIAs during 2001--2002 in areas where large birth cohorts, population density, hygiene, and climate favored poliovirus transmission. Six large-scale SIAs will be conducted in India in 2003 (two NIDs and four SNIDs), and two NIDs are planned for early 2004. Afghanistan, Egypt, Niger, Nigeria, Pakistan, and Somalia also will conduct multiple additional rounds of large-scale SIAs during 2003--2004.
The global funding gap for polio eradication is another challenge to the program. This financial shortfall for 2003--2005, resulting largely from the recent global economic slowdown, has resulted in a lack of resources available for SIAs in countries where polio was recently but not currently endemic and that remain at high risk for re-emergence of polio. To ensure activities will proceed for the second half of 2003, the polio partnership has appealed to donors to have funds in place before mid-2003.
Progress achieved in laboratory containment is encouraging, and planning for the post-eradication era has included ongoing evaluation of the scientific, economic, political, operational, and financial implications of policy options. An April 2002 meeting of public health leaders (primarily from developing countries) in Annecy, France, generated advice on the development of postcertification policies. A communications and public information plan will keep countries and interested parties abreast of the issues. The international community should make every effort to overcome remaining challenges and achieve a polio-free world.
* This decrease is primarily the result of a change in the methodology used to produce official national estimates in two countries (India and China).
Nationwide mass campaigns during a short period (days to weeks) in which 2 doses of OPV are administered to all children (usually aged <5 years), regardless of previous vaccination history, with an interval of 4--6 weeks between doses.
§ Campaigns similar to NIDs but confined to parts of the country.
¶ Two specimens collected at an interval of at least 24 hours, within 14 days of paralysis onset, and adequately shipped to the laboratory.
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