Progress Toward Poliomyelitis Eradication --- Afghanistan and Pakistan, January 2002--May 2003

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Since 1988, when the World Health Assembly resolved to eradicate poliomyelitis worldwide (1), the number of countries in which polio is endemic has decreased from 127 to seven, including Afghanistan and Pakistan (2). These two countries are considered one epidemiologic block because of their geographic proximity, frequent cross-border population movement, and the presence of genetically similar wild poliovirus (WPV) lineages. Although polio remains endemic in both countries, progress in interrupting poliovirus transmission has been substantial (3). This report describes intensified polio eradication activities in Afghanistan and Pakistan during January 2002--May 2003, summarizes progress made, and highlights the remaining challenges to interrupting poliovirus transmission.

Routine Vaccination

In 2002 in Afghanistan, reported national routine vaccination coverage of infants aged <12 months with 3 doses of oral poliovirus vaccine (OPV) was 48% (range: 6% [Urozgan]--84% [Nagarhar]) (Ministry of Health, unpublished data, 2003). In 2002 in Pakistan, coverage was 71% (Ministry of Health, unpublished data, 2003).

Supplementary Immunization Activities

Since 2000, Afghanistan and Pakistan have conducted frequent supplementary immunization activities (SIAs) that use house-to-house vaccine delivery, including at least four rounds of national immunization days (NIDs)* and three rounds of sub-NIDs (SNIDs)^† annually. Areas targeted for SNIDs are those in which various factors (e.g., surveillance results, genetic sequencing, supplementary or routine immunization coverage, and population dynamics) indicate a high risk for continuing virus transmission. In 2002, Pakistan conducted four rounds of NIDs and four rounds of SNIDs in close coordination with Afghanistan, which conducted five rounds of NIDs and three rounds of SNIDs. During 2003, planned SIAs include four rounds of NIDs (in April, May, September, and October) and three rounds of SNIDs (in March, July, and December) in Afghanistan and four rounds of NIDs (in March, April, September, and October) and four rounds of SNIDs (in January, June, July, and December) in Pakistan. In both countries, SIA quality is monitored by independent groups; university teachers and students (in Afghanistan) and private survey companies and university teams (in Pakistan) monitor SIA quality while rounds are being carried out and conduct immediate post-SIA coverage assessments.

To provide additional information about vaccination coverage, national polio eradication programs analyze the OPV vaccination status (routine and supplemental) of children with nonpolio acute flaccid paralysis (AFP) reported through the AFP surveillance system. During 2000--2002, the proportion of nonpolio AFP patients aged <24 months who received <3 OPV doses decreased from 72% to 18% in Afghanistan and from 46% to 28% in Pakistan.

Surveillance for AFP

The quality of AFP surveillance is evaluated by two key indicators established by the World Health Organization (WHO): sensitivity of reporting (target: nonpolio AFP rate of >1 case per 100,000 children aged <15 years) and completeness of stool specimen collection (target: two adequate stool specimens^§ from >80% of all persons with AFP). In 2002 in Afghanistan, the national nonpolio AFP rate was 3.3, and the adequate stool specimen collection rate was 81%; during January--May 2003, the nonpolio AFP rate increased to 3.8, and the adequate stool specimen collection rate increased to 85% (Table). In 2002, in Pakistan, the national nonpolio AFP rate was 2.8, reported nonpolio AFP rates in all provinces were >2.0, and adequate stool specimens were collected from 87% of persons with AFP; during January--May 2003, the nonpolio AFP rate increased to 3.0, and the adequate stool specimen collection rate increased to 89% (Table).

The WHO-accredited regional reference laboratory at the National Institutes of Health (NIH) in Islamabad, Pakistan, performs virologic testing of stool specimens from both Afghanistan and Pakistan, including primary virus isolation and intratypic differentiation (ITD). The nonpolio enterovirus (NPEV) isolation rate among stool samples (target: >10% isolation rate) is a combined indicator of the quality of specimen transport (i.e., maintenance of specimens at the appropriate temperature from time of collection until delivery to the laboratory) and sensitivity of laboratory processing. In 2002, NPEV isolation rates for Afghanistan and Pakistan were 15% and 19%, respectively; during January--May 2003, rates were 17% and 20%, respectively (Table). Laboratory efficiency is measured by the proportion of persons with AFP for whom virus isolation results are available within 28 days of receipt of specimens (target: 80% of persons with AFP). In 2002, the NIH laboratory reported final results for primary virus isolation within 28 days for 99% of specimens received from both Afghanistan and Pakistan. During January--May 2003, the proportion of specimen culture results that were reported within 28 days was 77% from Afghanistan and 94% from Pakistan (Table). During 2002--2003, for persons in whom poliovirus was isolated, the average interval between the onset of paralysis and the communication of final ITD results was 4--5 weeks.

Incidence of Polio

During 2001--2002, the number of polio cases in Pakistan that were confirmed virologically decreased from 119 (reported from 39 [29%] of 135 districts) to 90 (reported from 34 [25%] districts). In 2002, of 90 cases reported, 67 (74%) were WPV type 1 (P1), and 23 (26%) were WPV type 3 (P3). During January--May 2003, a total of 39 cases were reported from 20 (15%) districts, compared with 24 cases reported from 16 (12%) districts during the same period in 2002 (Figure). In 2001, of the 90 cases reported, 64 (71%) occurred in children aged <24 months; during January--May 2003, of the 39 cases reported, 22 (56%) occurred in this age group. In 2002, transmission in Pakistan occurred primarily in northern Sindh, the Peshawar area, the southern part of Northwest Frontier Province (NWFP), and southwestern Punjab; several areas considered previously to be virus reservoirs, (e.g., Karachi and Hyderabad in Sindh, the Quetta area in Balochistan, and the Bannu and Lakki Marwat districts in NWFP) reported few or no cases. In 2003, cases continued to be concentrated in two transmission zones (northern Sindh and northern NWFP) that were active in 2002, with some transmission in southwestern Punjab.

In 2002 in Afghanistan, 10 cases (five P1 and five P3) were reported from seven of 32 provinces, compared with 11 cases from six provinces in 2001. In May 2003, one case of P3 was reported from Nangarhar province; the most recent case reported previously was in December 2002 in the Southern Region; as of June 24, no other cases had been reported. Nangarhar province borders Pakistan, and genetic sequencing results indicate that this virus is related to those circulating across the border in NWFP. Sequencing results from the cases in Afghanistan in 2002 suggest that the only remaining endemic poliovirus reservoir in 2002 was in the southwestern part of the country, west of Kandahar. In 2003, no wild polioviruses had been isolated from this area as of June 24.

Genetic sequencing data from WPVs isolated from the Afghanistan/Pakistan epidemiologic block indicate that biodiversity continues to decrease. During 2000--2001, the number of virus lineage clusters for P1 decreased from 10 to six, and the number of clusters for P3 decreased from six to three. In 2002, five clusters (four P1 and one P3) accounted for 90% of confirmed cases from both countries.

Reported by: National Institutes of Health; Country Office of the World Health Organization; United Nations Children's Fund, Islamabad, Pakistan. Ministry of Public Health; Country Office of the World Health Organization; United Nations Children's Fund, Kabul, Afghanistan. Regional Office for the Eastern Mediterranean Region, World Health Organization, Cairo, Egypt. Dept of Vaccines and Biologicals, World Health Organization, Geneva, Switzerland. Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Global Immunization Div, National Immunization Program; Div of Nutrition and Physical Activity, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note:

Progress toward interrupting WPV transmission has continued in both Afghanistan and Pakistan despite armed conflict and ongoing political instability. Important achievements for 2002 include a reduction in the number of WPV cases, further restriction of poliovirus circulation to well-defined zones of transmission, and decreased genetic diversity of isolated wild polioviruses. In addition, both countries obtained support from the Global Alliance for Vaccines and Immunization to strengthen their routine vaccination programs.

Despite the progress made, critical challenges to achieving eradication remain in both countries, and overcoming surveillance quality gaps is of critical importance. Although Afghanistan began sentinel surveillance in 1997, systematic active surveillance at major health facilities was initiated only recently. In Pakistan, genetic data for 2002--2003 indicate that surveillance might have missed ongoing transmission for prolonged periods in some areas, including northern NWFP and southern Punjab. In both countries, analysis of OPV status among nonpolio AFP patients indicates that vaccination teams missed a substantial number of children aged <24 months during recent campaigns. Although Afghanistan has returned program quality to levels achieved before armed conflict began in late 2001, increasing security problems within the country, particularly in the south and southeast, have limited access to critical areas during SIAs and might have compromised the quality of AFP surveillance.

For the polio eradication activities in the remaining transmission zones to be improved, close collaboration between the national governments and their partners^¶ and between the Afghanistan and Pakistan programs are critical. A comprehensive communication and advocacy strategy is needed to help motivate and engage district governments and communities, reach persons at high risk during SIAs, and strengthen vaccination teams. For surveillance quality to be improved further and maintained, AFP surveillance performance indicators should be monitored continuously, particularly to detect inadequate performance at the subnational level.

Through the efforts of thousands of health-care workers and volunteers, Afghanistan and Pakistan have made progress toward interrupting WPV transmission. Polio teams in both countries, with government support and commitment, have implemented high-quality strategies. For polio to be eradicated, maintaining this commitment and improving the quality of activities in the remaining transmission zones should be a priority of the national and local governments and their partners.

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Progress Toward Poliomyelitis Eradication --- Afghanistan and Pakistan, January 2002--May 2003

Routine Vaccination

Supplementary Immunization Activities

Surveillance for AFP

Incidence of Polio

Editorial Note:

References

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