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Progress Toward Poliomyelitis Eradication --- Pakistan and Afghanistan, January 2006--February 2007

Of the four countries where wild poliovirus (WPV) transmission has never been interrupted, two are in the World Health Organization's (WHO) Eastern Mediterranean Region: Pakistan and Afghanistan (1).* During January 2006--February 2007, the number of reported WPV cases in both countries increased. In addition, an increase was observed in the number of affected districts; however, genetic diversity of the virus decreased, and regions of transmission remained limited. This report updates a previous report (2) and describes polio cases and eradication activities in Pakistan and Afghanistan during January 2006--February 2007. Critical to the success of polio eradication will be high vaccination coverage among children in areas of frequent conflict along the border between these two countries.

Immunization Activities

Routine coverage of infants with 3 doses of oral polio vaccine (OPV) remained low in 2006, at 69% and 64% in Afghanistan and Pakistan, respectively. Reported 3-dose OPV coverage, however, varied substantially among provinces within each country, ranging from 20% to 80% in Afghanistan, and from 42% to 90% in Pakistan. Coverage was higher in areas with good health infrastructure and management, easy access, and higher levels of literacy.

In 2006, Pakistan conducted 12 supplemental immunization activities (SIAs),§ consisting of six national immunization days (NIDs), two sub-NIDs (SNIDs), three large-scale SIAs in response to reported WPV cases, and one cross-border SIA in collaboration with Afghanistan. SNIDs in Pakistan were conducted primarily in districts at high risk for poliovirus circulation, including semiautonomous tribal areas of North-West Frontier Province; districts of Balochistan Province, bordering Afghanistan; and Sindh Province (including Karachi city). During 2006, Afghanistan conducted five NIDs and five SNIDs, with most SNIDs covering the southern, southwestern, and eastern regions along the border with Pakistan. During the first 2 months of 2007, Pakistan conducted two SIAs (one NID and one SNID), and Afghanistan conducted two SNIDs.

SIAs in both countries continued to be effective, with vaccination rates estimated at >95% among children aged <5 years. However, evidence from post-SIA assessments, field observations, and reported vaccination histories of acute flaccid paralysis (AFP) cases indicates that vaccination coverage remains suboptimal, particularly in the known high-risk, security-compromised, and remote areas along the border between the two countries. In Pakistan, these areas include parts of the Federally Administered Tribal Areas, North-West Frontier Province, and Balochistan Province. In Afghanistan, the most serious security situation persists in the Southern Region (Kandahar, Helmand, Oruzgan, and Zabul provinces), but security also is compromised in large parts of the South Eastern Region and in parts of the Eastern Region. Because of the extensive cross-border movement and migration between Pakistan and Afghanistan, especially in the region stretching from central Pakistan through Balochistan into southern Afghanistan, SIAs in the two countries generally were synchronized to ensure simultaneous, comprehensive coverage of border areas and of children in transit.

In 2006, monovalent type 1 OPV (mOPV1), which is most effective against the outbreak serotype, WPV type 1 (WPV1) (3), was used in most high-transmission risk areas during four of the 12 SIAs conducted in Pakistan, and five of the 10 SIAs in Afghanistan. However, in Pakistan, since the November 2006 SIA, only trivalent OPV (tOPV) has been used in SIAs because of the persistent transmission of both WPV1 and WPV type 3 (WPV3). In 2007, the extent of mOPV1 use in SIAs in both countries will depend on the types of poliovirus circulation.

Acute Flaccid Paralysis (AFP) Surveillance

The Global Polio Eradication Initiative relies on an acute flaccid paralysis (AFP) surveillance system to identify cases of poliomyelitis. Through this system, AFP cases in all children aged <15 years and suspected polio in persons of any age are reported and investigated as possible poliomyelitis. AFP surveillance quality is monitored according to World Health Organization (WHO) operational targets.** The national nonpolio AFP rate (number of nonpolio AFP cases per 100,000 population aged <15 years) was 5.8 in Pakistan and 6.2 in Afghanistan, above the target rate of two cases; adequate stool specimens†† were collected from 89% (range: 82%--95% among provinces) and 91% (range: 64%--100% among provinces) of AFP cases in Pakistan and Afghanistan, respectively, above the target of 80% (Table).

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, continues to provide laboratory support for AFP surveillance in both countries. The National Institutes of Health laboratory performs the initial virus isolation, intratypic differentiation, and genomic sequencing. Since July 2006, the laboratory has implemented a fast-processing algorithm, which shortens the interval between receiving the specimen and reporting the results to approximately 14 days (an approximate 50% reduction).

WPV Incidence

In Pakistan, the number of confirmed polio cases increased from 28 cases reported from 17 districts in 2005 to 40 cases reported from 20 districts in 2006. Of the 40 polio cases, 20 were caused by WPV1 and 20 by WPV3. The majority of WPV1 cases were reported from Sindh Province or from security-compromised areas in North-West Frontier Province (Figure). Approximately 73% of polio patients were aged <2 years, 13% had never received any OPV doses, and 18% had received 1 to 3 OPV doses. Additionally, 18% of patients were of Afghani origin, a group that accounts for approximately 2% of the total Pakistan population. The resurgence of WPV3 in Pakistan was reported in late 2006 in northern Sindh and North-West Frontier Province, caused by a virus strain that had circulated in southern Afghanistan in 2005 and early 2006 and was reintroduced into Pakistan through Balochistan Province. The virus spread most rapidly in Sindh, and by February 2007, a total of 10 WPV3 cases had been reported from eight districts. As of February 28, six cases (two WPV1 and four WPV3) had been confirmed.

In Afghanistan, 31 WPV cases were reported in 2006 (29 WPV1 and two WPV3), up from nine total cases in 2005 (2). After nearly 2 years without a report of WPV1 in the Southern Region, an importation of WPV1 from Pakistan in late 2005 resulted in an outbreak that peaked in June--July 2006 and ended in early September 2006. Apart from this regional outbreak, Afghanistan reported only two WPV1 cases (one from Nangarhar Province, Eastern Region, and one from Baghlan Province, North Eastern Region). Neither of these cases led to extended virus transmission, and genetic data suggest that both cases were imported recently from the Southern Region outbreak area or from Pakistan. Both 2006 WPV3 cases were reported from the Southern Region. Twenty (65%) of 31 cases reported in 2006 were among children aged <2 years; six (19%) of those children had never received OPV, and 10 (32%) had received 1 to 3 doses of OPV. In 2007, no polio cases had been reported from Afghanistan as of February 28. However, the security-compromised, hard-to-access area around Kandahar, Southern Region (adjacent to the Quetta area of Balochistan, Pakistan) remains the area at greatest risk for undetected poliovirus transmission. In previous outbreaks, circulating virus has been reported in Kandahar with subsequent spread to other provinces in western and central Afghanistan.

Genetic sequencing revealed that five clusters of genetic lineages of WPV1 and two clusters of WPV3 circulated in Pakistan and Afghanistan in 2006, a decrease in the number of lineages from seven WPV1 and three WPV3 in 2005. The genetic data also suggested strong links between viruses reported in Pakistan and Afghanistan.

Reported by: WHO Eastern Mediterranean Regional Office Egypt, Cairo; WHO Pakistan, Islamabad; WHO Afghanistan, Kabul; Immunization, Vaccines, and Biologicals Dept, WHO, Geneva, Switzerland. Global Immunization Div, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note:

Although the number of confirmed polio cases increased during 2006 in both Pakistan and Afghanistan, some progress was made toward the eradication goal in both countries. WPV transmission in Pakistan in 2006 was confined to previously known areas of transmission: south and central North-West Frontier Province; the Quetta area of Balochistan, bordering the Southern Region of Afghanistan; and Karachi in Sindh. After the use of mOPV1 during several SIAs since 2005 (3), WPV1 transmission in Pakistan was lower in 2006 than in any previous year since poliovirus type has been measured, with only one WPV1 case each reported from Punjab Province and from northern Sindh. In Afghanistan, the WPV1 outbreak in the southern area of the country ended, with no further reports of WPV1 from the area since early September 2006. Although WPV1 was imported into two other regions of Afghanistan, the virus did not spread. In addition, the genetic diversity of both types of WPV circulating in Afghanistan and Pakistan continued to decrease, and AFP surveillance remained sensitive in both countries.

Vaccinating children in areas of conflict remains one of the greatest challenges in both countries and will require continued engagement of civil administration and local communities, including support from tribal and religious leaders. Additional focus has been placed on the identification of and access to mobile populations in areas of high poliovirus transmission. Cross-border coordination of polio activities, including two joint SNIDs, indicates government commitment to the program in both countries. The two respective ministers of health conducted a meeting on polio and jointly inaugurated the cross-border mop-up vaccination campaign in December 2006. The number of permanent vaccination posts at the border also was increased from two to 15.

Interruption of WPV transmission in Pakistan and Afghanistan is a regional and global priority. Success will require overcoming one of the greatest challenges to polio eradication: accessing and vaccinating children along the large, remote, and increasingly security-compromised border between the two countries. This area is now recognized as the principal remaining virus reservoir in the region and a primary source of poliovirus spread into other areas, facilitated by frequent border crossings. Achieving a high rate of vaccination coverage in this border area will require continued support from the international polio partnership,§§ commitment to high-quality SIAs from political and health leaders at all levels, and close coordination of polio eradication activities between the two countries.

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---Pakistan and Afghanistan, January 2005--May 2006. MMWR 2006;55:679--82.
  3. Caceres VM, Sutter RW. Sabin monovalent oral polio vaccines: review of past experiences and their potential use after polio eradication. Clin Infect Dis 2001;33:531--41.

* The other two countries are India and Nigeria.

Sources of coverage data are unpublished reports from the Ministry of Health on routine immunization coverage (Afghanistan) and an independent coverage evaluation conducted in May 2006 (Pakistan).

§ Mass campaigns conducted during a brief period (days to weeks) in which 1 dose of OPV is administered to all children aged <5 years, regardless of vaccination history. The geographic extent of campaigns (national versus subnational) is determined by analysis of surveillance data. OPV can be administered at fixed sites, by mobile teams during house-to-house visits, by mobile teams at transit points (e.g., train stations or markets), or through a combination of strategies, depending on local circumstances.

mOPV1 contains polio vaccine against WPV1 only and does not provide protection against other WPV types. mOPV1 provides greater immunity to a specific WPV type than does the same number of doses of trivalent OPV.

** Current WHO operational targets for countries at high risk for polio transmission are a nonpolio AFP rate of at least two cases per 100,000 population aged <15 years at each subnational level and adequate stool specimen collection for >80% of AFP cases (i.e., two specimens collected >24 hours apart, both within 14 days of paralysis onset, and shipped on ice or frozen ice packs to a WHO-accredited laboratory and arriving at the laboratory in good condition).

†† Two stool specimens collected 24 hours apart within 2 weeks of paralysis onset that arrive at the lab 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: 4/12/2007

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