Progress Toward Poliomyelitis Eradication --- Pakistan and Afghanistan, 2007

Of the four countries worldwide where wild poliovirus (WPV) transmission has never been interrupted,* Pakistan and Afghanistan are considered a single epidemiologic block. (1). Use of intense poliomyelitis eradication measures, including close coordination between the two countries and increased use of monovalent oral poliovirus vaccines (mOPVs) against type 1 WPV (WPV1) and type 3 WPV (WPV3), has reduced WPV transmission to historically low levels. However, despite these efforts, in 2007 both types of WPV continued to circulate in areas of Pakistan and Afghanistan. Ongoing conflicts and security concerns in remote areas with rugged terrain limit access to children and decrease vaccination coverage from routine and supplementary immunization activities (SIAs)^† in border areas of both countries where WPV transmission is endemic. In other WPV-endemic areas of Pakistan, where security and access concerns do not exist, operational problems in implementing SIAs resulted in inadequate vaccination of children, which failed to interrupt WPV transmission. This report updates previous reports (2) and describes polio eradication activities in Pakistan and Afghanistan during January--December 2007 (data as of March 22, 2008). Further progress toward polio eradication will require continued measures to address security concerns in portions of both countries and problems with implementing SIAs in secure areas of Pakistan.

Immunization Activities

Estimated routine vaccination coverage of infants with 3 doses of oral poliovirus vaccine (OPV3) in 2006^§ was 83% nationally in Pakistan and 77% in Afghanistan (3). However, OPV3 coverage varied substantially among districts within each country; in Pakistan, 46 (35%) of the 132 districts reported infant OPV3 coverage below 80%, with 13 (10%) districts reporting <60% coverage. Reported infant OPV3 coverage data for Afghanistan, which are less reliable, ranged as low as 32% among the 329 districts.

Both Pakistan and Afghanistan conducted large-scale house-to-house SIAs with oral polio vaccine (OPV) during 2007, targeting children aged <5 years. Pakistan conducted four national immunization days (NIDs) and seven subnational immunization days (SNIDs) in the Federally Administered Tribal Areas and districts of North-West Frontier Province (NWFP), in districts in the Quetta area of Balochistan province bordering Afghanistan, in southern Punjab, and in Sindh province (including the city of Karachi) (Figure). Afghanistan also conducted four NIDs and seven SNIDs in its south, southeast, and east regions, along the border with Pakistan. Because of extensive cross-border movement and migration between the two countries extending from central Pakistan through Balochistan into southern Afghanistan, SIAs were synchronized largely to optimize simultaneous, comprehensive coverage of border areas and of children in transit. Because of circulation of both WPV1 and WPV3, both countries used type 1 and type 3 mOPV (mOPV1 and mOPV3) in addition to trivalent OPV (tOPV) alone or in combination with mOPVs at different times on a district basis during the 2007 SIAs (Table 1).

Overall reported vaccination coverage achieved after SIAs was reported to be consistently >95% at the district level in Pakistan and the province level in Afghanistan. However, these reports might overestimate district coverage; in addition, an analysis of post-SIA coverage at the subdistrict (union council) level in high-risk districts of Pakistan found reported coverage below the district average of approximately 95% in 20% of union councils. In particular, coverage remained suboptimal in security-compromised and remote areas along the border in both countries.

In 2007, efforts continued in Afghanistan to get agreement from all partners on ceasing hostilities during SIAs to allow vaccinators to safely reach all children. Indirect contact was made with antigovernment groups; since August 2007, these groups have publicly supported polio eradication and SIAs in their areas of influence. However, both post-SIA evaluation data and data on OPV status of investigated cases document that up to 20% of children still continue to be missed in some areas of southwest Afghanistan.

Acute Flaccid Paralysis (AFP) Surveillance

High-quality AFP surveillance was maintained in both countries in 2007.^¶ The nonpolio AFP rate (number of nonpolio AFP cases per 100,000 population aged <15 years) at the national level was 5.6 in Pakistan (range among four provinces and other areas: 3.3--8.3) and 6.9 in Afghanistan (range among eight regions: 5.0--8.9) (Table 2). The percentage of AFP cases with collection of adequate stool specimens was 91% both in Pakistan (range: 83%--96%) and in Afghanistan (range: 87%--100%).

The polio laboratory at the National Institutes of Health in Islamabad, Pakistan, which serves as a Regional Reference Laboratory in the global polio laboratory network, provides laboratory support for AFP surveillance in both countries, including genomic sequencing. During 2007, the polio laboratory processed 13,513 stool specimens from both countries, with 10,845 (80%) of the specimens from AFP cases and the remaining specimens from contacts of persons with AFP.

WPV Incidence

The number of confirmed polio cases in Pakistan decreased from 40 reported from 22 districts in 2006 to 32 cases reported from 18 districts in 2007 (Figure and Table 2). Of polio cases reported in 2007, 19 (59%) were caused by WPV1 and 13 (41%) by WPV3, compared with 20 (50%) cases each caused by WPV1 and WPV3 in 2006. In 2007, 21 (66%) of the cases were among children aged <3 years. Among the 31 children with WPV for whom vaccination data were available, a substantial proportion were undervaccinated for their age; six (19%) had never received any OPV doses, and six (19%) had received 1--3 OPV doses. The median OPV doses received by children with polio was 6, compared with a median of 15 doses received by children with nonpolio AFP reported in 2007.

In Afghanistan, 17 confirmed polio cases were reported from 13 districts in 2007, compared with 31 from 17 districts in 2006 (Figure and Table 2). Of polio cases reported in 2007, six (35%) were caused by WPV1, and 11 (65%) were caused by WPV3, compared with 29 (94%) caused by WPV1 and two (6%) caused by WPV3 in 2006. Among children with WPV in 2007, 16 (94%) were aged <3 years, including 10 (59%) who were aged <2 years. Four (24%) of the 17 children with polio had never received OPV before, and six (35%) had received 1--3 OPV doses. The median OPV doses received by children with polio was 2, compared with a median of 12 doses received by children with nonpolio AFP reported in 2007.

Transmission of WPV in Pakistan and Afghanistan has occurred largely in two zones, with limited movement of WPV between these two zones occurring in Pakistan. The northern transmission zone in Pakistan, which reported 10 WPV1 cases and one WPV3 case in 2007, makes up most of NWFP, including the tribal agencies along the border with Afghanistan (Figure). The east region of Afghanistan that borders this area of Pakistan reported two WPV1 cases in early 2007. The southern transmission zone, which forms a corridor from the south region of Afghanistan into Pakistan through Balochistan and southern Punjab into northern and southern Sindh (including Karachi), remained the principal transmission zone in 2007. Pakistan reported nine WPV1 and 12 WPV3 cases from this zone in 2007, and the adjacent south region of Afghanistan reported four WPV1 cases and 11 WPV3 cases. In 2007, 23 (96%) of 24 WPV3 cases in the two countries were reported from the southern zone, with no WPV3 case reported from the northern zone since January 2007. Genetic sequencing data of all isolates confirmed shared circulation of WPVs in Pakistan and Afghanistan in the two transmission zones.

In 2008, through mid-March, WPV transmission had continued in Pakistan, with three cases of WPV1 reported from north-central Sindh Province. WPV transmission also had continued in Afghanistan, with three cases of WPV1 reported from the south region (two cases) and adjacent west region (one case), and one case of WPV3 reported from the south region.

Reported by: World Health Organization (WHO) Eastern Mediterranean Regional Office Egypt, Cairo; WHO Pakistan, Islamabad; WHO Afghanistan, Kabul; Polio Eradication Dept, WHO, Geneva, Switzerland. Global Immunization Div, Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note:

In 2007, limited progress was made toward interrupting WPV transmission in Pakistan-Afghanistan. The number of polio cases was reduced, as was the geographic extent of poliovirus transmission in Pakistan and Afghanistan. In Afghanistan, increased use of mOPV1 and reduced use of type 3-containing OPV led to a decrease in WPV1 cases from 2006 but an increase in WPV3 cases. The majority of the population in both countries live in polio-free areas; Pakistan's largest province, Punjab (with >65% of the total population), reported only one case of WPV3 in 2007 and no cases of WPV1 since mid-2006. AFP surveillance remains highly sensitive in both countries, including in most of the insecure border areas. In Afghanistan, a breakthrough occurred in August 2007 when the support of antigovernment groups was obtained, which increased areas accessible to vaccinators during SIAs in the south region and resulted in improved coverage of SIAs during September--December 2007. Nonetheless, transmission continued in remote areas affected by ongoing conflict and security problems.

Despite implementation of 11 SIAs, WPV transmission continued in the same areas of Pakistan as in previous years for two main reasons. First, reaching children during SIAs in insecure areas remains one of the greatest challenges in both countries and will need continued engagement of civil administration and local communities, including support from tribal and religious leaders. Second, implementation of SIAs remains weak in the remaining WPV-endemic areas of the Pakistani provinces of Sindh and Balochistan, where no access or security concerns exist. Other secure areas of Pakistan succeeded in interrupting WPV transmission several years ago. The Technical Advisory Group on Polio Eradication for Afghanistan and Pakistan recommended at its February 2008 meeting that the government of Pakistan take all necessary steps to ensure that health and political leaders in affected districts assure that SIA rounds reach the highest possible coverage.

Prompt interruption of WPV transmission in Pakistan and Afghanistan is a regional and global priority. In addition to continued support from the international polio eradication partnership,** success will require overcoming one of the most important remaining challenges in polio eradication globally: the barrier to vaccination of children in large, remote, and security-compromised areas. Critical improvements are needed in the quality of SIAs and delivery of routine immunization, particularly in the Pakistan provinces of Sindh and Balochistan, to further limit transmission.

References

1. CDC. Progress toward interruption of wild poliovirus transmission---worldwide, January 2006--May 2007. MMWR 2007;56:682--5.
2. CDC. Progress toward poliomyelitis eradication---Pakistan and Afghanistan, January 2006--February 2007. MMWR 2007;56:340--3.
3. WHO vaccine-preventable diseases monitoring system: 2007 global summary. Geneva, Switzerland: World Health Organization. Available at http://whqlibdoc.who.int/hq/2007/who_ivb_2007_eng.pdf.

* The other two countries where WPV transmission has never been interrupted are India and Nigeria.

^† Mass campaigns conducted for a brief period (days to weeks) in which 1 dose of oral poliovirus vaccine is administered to all children aged <5 years, regardless of vaccination history.

^§ Most recent year for which data are available; World Health Organization (WHO)/UNICEF estimates.

^¶ The quality of AFP surveillance is monitored by three performance indicators: 1) detection rate of AFP cases not caused by WPV, 2) the proportion of AFP cases with adequate stool specimens, and 3) the proportion of stool specimens processed in a WHO-accredited laboratory. Current WHO operational targets for countries with endemic polio transmission are a nonpolio AFP detection rate of at least two cases per 100,000 population aged <15 years and adequate stool-specimen collection from >80% of AFP cases, in which two specimens are collected >24 hours apart, both within 14 days of paralysis onset, and shipped on ice or frozen ice packs to a WHO-accredited laboratory, arriving in good condition.

** Polio eradication efforts in Afghanistan and Pakistan are supported by the Bill and Melinda Gates Foundation; the governments of Japan, the Netherlands, and the United Kingdom; the International Committee of the Red Cross; the International Federation of Red Cross and Red Crescent Societies; Rotary International; UNICEF; the United States Agency for International Development; WHO; and CDC.

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Date last reviewed: 3/26/2008