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Progress Toward Poliomyelitis Eradication --- Pakistan and Afghanistan, January 2005--May 2006

As of March 2006, wild poliovirus (WPV) remained indigenous in four countries: Afghanistan, India, Nigeria, and Pakistan (1). Since 2005, WPV-endemic countries in Asia have intensified their polio eradication measures through use of type 1 monovalent oral polio vaccine (mOPV1)* and implementation of innovative social mobilization, communication, and vaccine-delivery strategies (2,3). This report describes polio eradication strategies in Afghanistan and Pakistan during January 2005--May 2006.

Immunization Activities

Routine vaccination coverage with oral polio vaccine (OPV) remains low in Afghanistan and in much of Pakistan (2). The most recent available estimates (2004) for national vaccination coverage of infants with 3 doses of OPV are 66% for Afghanistan and 65% for Pakistan (4). However, population figures for Afghanistan are uncertain, and coverage in both countries varies among provinces and districts.

During 2005--2006, both countries continued to vaccinate children aged <5 years with additional OPV doses during large-scale, closely synchronized, house-to-house immunization campaigns, or supplementary immunization activities (SIAs). In 2005, Pakistan conducted eight SIAs (seven national immunization days [NIDs] and one subnational immunization day [SNID]), and Afghanistan conducted 10 SIAs (four NIDs, three SNIDs and three mop-up campaigns). In 2006, both countries conducted an SIA in January (NID in Pakistan and SNID in Afghanistan), March (NID in each country), and April (NID in each country), followed in early May by the first of two mop-up SIAs targeting the region stretching from central Pakistan into southern Afghanistan (Figure). A second SIA targeting the same area was held in early June 2006.

Pakistan used mOPV1 in the September 2005 NID and in all subsequent rounds through April 2006. The extent of mOPV1 use varied by round but always included known areas of high risk in Northwest Frontier Province (NWFP) and Punjab and Sindh provinces. Because of WPV type 3 (WPV3) circulation in Balochistan, mOPV1 use in that province was delayed until the December 2005 SNID. In Afghanistan, mOPV1 was used in three rounds: in October 2005 in two provinces in the eastern region, during the April 2006 NID round in the southern region, and in the May 2006 mop-up in the southern, southeastern, and eastern regions.

Both countries deployed additional partner staff members from areas at lower risk to areas at higher risk. Since January 2005, SIA staff members have targeted mobile groups (e.g., nomads, seasonal migrants and persons seeking temporary employment in harvesting, Afghan refugees moving between countries, and groups moving out of areas with ongoing military conflict) throughout the region with high virus transmission between central Pakistan and southern Afghanistan.

Polio teams in both countries had difficulties gaining access to children and effectively implementing SIAs in several areas affected by conflict. In Pakistan, these areas included the North Waziristan, South Waziristan, and Bajaur agencies in the tribal area of NWFP, and, since mid-2005, two districts in eastern Balochistan (Dera Bugti and Kohlu). Worsening security had the greatest impact on the effectiveness of the vaccination campaign in the southern region of Afghanistan, despite strategies to overcome the problems (e.g., recruitment of additional local staff members).

Acute Flaccid Paralysis (AFP) Surveillance

AFP reporting increased in both countries in 2005 compared with 2004; nonpolio AFP reporting rates were more than five cases per 100,000 population aged <15 years, and adequate stool specimens§ were collected from 89% and 92% of persons with AFP in Pakistan and Afghanistan, respectively. AFP surveillance remained above certification-standard levels at the national level in both countries, provincial level in Pakistan, and regional level in Afghanistan. However, genetic analysis in 2005 and 2006 identified WPV chains of transmission in both countries that might have existed for 2--3 years without being detected by AFP surveillance. The primary gaps in surveillance are in southern Afghanistan.

AFP surveillance in Pakistan and Afghanistan continues to receive laboratory support from the National Institutes of Health in Islamabad, Pakistan. In 2005, the laboratory isolated nonpolio enteroviruses from 19% and 22% of specimens from Pakistan and Afghanistan, respectively.

Polio Incidence

In Pakistan, 28 polio cases were confirmed with onset in 2005 (Table), compared with 53 cases in 2004. Twenty-seven of the 2005 cases were WPV1, and one was WPV3 (from Quetta district in the Balochistan province). For the first time, no high-season (August--October) transmission peak occurred; 13 cases were reported during this period in 2005. In 2006, as of May 31, four cases (three WPV1 and one WPV3) had been confirmed: one WPV1 case from Killa Abdullah in the Balochistan province (February 23 onset of paralysis); one WPV1 case from Dera Ismail Khan district in NWFP (February 23 onset of paralysis); one WPV1 case from Karachi in the Sindh province (April 28 onset of paralysis); and one WPV3 case from Jafarabad in the Balochistan province (May 15 onset of paralysis).

In Afghanistan, nine polio cases with onset in 2005 were confirmed (five WPV1 and four WPV3), all from three provinces in the southern region: three WPV1 and two WPV3 cases from Helmand, two WPV3 cases from Oruzgan, and two WPV1 cases from Kandahar. In 2006, WPV1 transmission is continuing in the southern region. As of May 31, eight WPV1 cases had been reported, including seven from Kandahar (three from Spin Boldak district and four cases from districts near the city of Kandahar) and one from Helmand. A WPV3 case with onset of paralysis on May 4 was also reported from Helmand province. During 2005--2006, confirmed WPV cases (both WPV1 and WPV3) in Afghanistan have been limited to three provinces of the southern region: Helmand, Oruzgan, and Kandahar. Only one case in 2004 and one positive contact (i.e., a person who is excreting WPV but has no paralysis) in 2005 were reported from the eastern region.

During 2005 and 2006, WPV detection in Afghanistan and Pakistan has been limited to five zones known for endemic transmission in preceding years: 1) Peshawar Valley and surrounding districts in NWFP, Pakistan; 2) southern Punjab, Pakistan; 3) northern Sindh, Pakistan; 4) eastern Balochistan and the Quetta area (including Pishin and Killa Abdullah districts) of Balochistan, Pakistan; and 5) the southern region of Afghanistan, particularly Kandahar, Helmand, and Oruzgan provinces.

Genetic data indicate close links between viruses found in zones 2 through 5 and confirm that these zones form a transmission corridor. All cases in Afghanistan since January 2005 and 24 of the 31 cases reported in Pakistan during the same period occurred in zones along this corridor. Genetic analysis indicates that the biodiversity of endemic WPVs has continued to decrease in Pakistan; the number of type-1 lineage clusters (substrains) decreased from six in 2004 to three in 2005; one cluster of WPV1 has been identified in 2006.

Reported by: Immunization, Vaccines, and Biologicals Dept, World Health Organization (WHO), Geneva, Switzerland. WHO Pakistan, Islamabad. Global Immunization Div, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note:

Pakistan and Afghanistan continue to progress toward polio eradication. Approximately 50% fewer cases were reported in Pakistan in 2005 than in 2004. For the first time since polio eradication measures began in Pakistan, no seasonal peak of cases was recorded during the 2005 autumn high-transmission season, indicating a decrease in WPV circulation after the SIAs. As of May 31, 2006, four cases had been reported in Pakistan, fewer than the number reported during any previous first quarter.** Epidemiologic findings suggest that the geographic extent of WPV transmission narrowed at the end of 2005; therefore, transmission is now confined to a corridor linking central Pakistan with southern Afghanistan through Balochistan. The reduction in the biodiversity of viral isolates indicates that previous transmission chains have been interrupted.

Although the number of WPV cases in Afghanistan increased from five in 2004 to nine in 2005, transmission was confined to three (9.4%) of 32 provinces, all in the southern region; transmission in 2004 also was confined to three provinces (although different from the 2005 provinces). Three genetically different clusters of WPV3 circulated in the south in 2005, and at least one WPV3 strain persisted in 2006. Cross-border transmission of WPV1, particularly in Kandahar, increased toward the end of 2005. The likely reason for continued transmission in southern Afghanistan is the lack of security in that area, which hinders planning, implementation, and evaluation of SIAs.

Cultural ties between southeastern Afghanistan and bordering areas of Pakistan are close, particularly between the Kandahar area and Balochistan, where cross-border migration is common. Unless transmission is stopped in this region, preventing continued transmission will be difficult in other parts of the high-risk corridor of districts from Afghanistan to central Pakistan.

Stopping WPV transmission in Afghanistan and Pakistan calls for additional improvements in SIA quality, particularly higher coverage of mobile persons (e.g., nomads or migrants) in areas of Pakistan at high risk and improved access to children in southern Afghanistan. These improvements will require increased deployment of local health workers and volunteers and an appeal to those in the southern Afghanistan conflict to reinstitute immediately a cease-fire to allow vaccinators to do their work undisturbed.

Progress in polio eradication has resulted from support from the international polio partnership†† and political and health leaders at the national, provincial, and district levels. The goal of polio eradication can be achieved only if health and political leaders remain committed to and supportive of their national programs.

References

  1. CDC. Progress toward interruption of wild poliovirus transmission---worldwide, January 2005--March 2006. MMWR 2006;55:458--62.
  2. CDC. Progress toward poliomyelitis eradication---Afghanistan and Pakistan, January 2004--February 2005. MMWR 2005;54:276--9.
  3. CDC. Progress toward poliomyelitis eradication---India, January 2004--May 2005. MMWR 2005;54:655--9.
  4. World Health Organization. WHO vaccine-preventable diseases: monitoring system, 2005 global summary. Geneva, Switzerland: World Health Organization; 2005. Available at http://www.who.int/vaccines-documents.

* mOPV1 contains polio vaccine virus against type 1 WPV (WPV1) only and does not provide protection against other WPV types; mOPV1 provides greater immunity to WPV1 than does trivalent OPV using the same number of doses.

SIAs in a targeted geographic area of known virus transmission.

§ Two stool specimens that are collected at an interval of at least 24 hours within 14 days of paralysis onset and properly shipped to the laboratory.

Nonpolio AFP rate of at least two cases per 100,000 population aged <15 years and collection of two adequate stool specimens from at least 80% of all AFP cases.

** As of May 31, 2006; laboratory data were complete through mid-April.

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

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Figure 1
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