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Progress Toward Poliomyelitis Eradication -- Pakistan, 1994-1998

Since the 1988 World Health Assembly resolution to eradicate poliomyelitis by 2000, polio cases reported globally have decreased by approximately 85% (1). Despite a strong commitment to polio eradication, polio remains endemic in Pakistan. In 1997, Pakistan reported 1147 polio cases, representing widespread poliovirus circulation nationally and constituting 22% of cases reported worldwide. However, surveillance and laboratory data from 1998 indicate that previous widespread poliovirus circulation was geographically localized for the first time. This report describes polio eradication activities in Pakistan, including the impact of routine and supplementary vaccination on polio incidence.

Routine Vaccination Coverage

Reported routine vaccination coverage with three or more doses of oral poliovirus vaccine (OPV3) among children aged less than or equal to 1 year decreased from 83% in 1990 to 57% in 1995, and increased to 75%-81% during 1996-1998 (Figure_1). In Pakistan during January 1998, cluster surveys conducted in 13 districts revealed a median routine OPV3 coverage of 58% (range: 10%-93%), compared with 71% coverage based on administrative data.

Supplementary Vaccination Coverage

National Immunization Days * (NIDs). Annual NIDs, which delivered two doses of OPV to all children aged less than 5 years, began in Pakistan in 1994. Since then, greater than 20 million children have been vaccinated each year, with coverage reported at greater than 95% during each of 10 NID rounds. NIDs in 1994 and 1995 were conducted during high poliovirus transmission season to coordinate with NIDs held in neighboring countries; subsequent NIDs have been conducted during Pakistan's low polio season during December- February. In three districts following the December 1997 NID, cluster surveys revealed a median coverage of 87%. NIDs also were conducted in December 1998 (round 1) and January 1999 (round 2); during the first round, 26 million children were vaccinated, representing the highest number of children vaccinated in Pakistan.

Cross-border vaccination activities. Pakistan implemented cross-border supplemental vaccination activities in all districts bordering Iran and Afghanistan. During NIDs in Iran in March and April 1998, an average of 177,000 Pakistani children (85% of the target) were vaccinated in each of two rounds through house-to-house vaccinations in five border districts in Balochistan. During NIDs in Afghanistan in May and June 1998, 2,110,000 (round 1) and 1,660,000 (round 2) Pakistani children were vaccinated in 22 districts in Balochistan and Northwest Frontier Province (NWFP), reaching greater than 100% of target children in each round. Outbreak response. Outbreak response consisted of administering two doses of OPV to children aged less than 5 years through house-to-house vaccinations throughout the outbreak district. In 1997, approximately 200,000 children were vaccinated during each of two rounds in the districts of Bannu, Lakkimarwat, and Quetta.

Acute Flaccid Paralysis Surveillance

Acute flaccid paralysis (AFP) surveillance was introduced in Pakistan in 1995, and by 1998, staff in all provinces were trained in AFP surveillance and were sending monthly case reports to the Expanded Program on Immunization (EPI) office. AFP surveillance was strengthened through surveillance assessments in many districts and introduction of computerized case line listings at the provincial and national levels. The poliovirus laboratory at the National Institutes of Health in Islamabad serves as both the National Poliomyelitis Laboratory and the WHO Regional Reference Laboratory for Poliomyelitis; it performs primary poliovirus isolation from stool specimens and intratypic differentiation of poliovirus.

To monitor AFP surveillance performance, a reported nonpolio AFP rate of greater than or equal to 1 per 100,000 population aged less than 15 years is used to indicate a sensitive AFP surveillance system. In 1997, the nonpolio AFP rate was 0.7 nationally and was less than 1 in all provinces and territories (Table_1). During January-November 1998, the nonpolio AFP rate was 0.6, with no increase in case findings compared to 1997. The proportions of cases with adequate stools (61%) and 60-day follow-up for residual paralysis (75%) increased in 1998; however, the goals of reaching 80% for both parameters have not been achieved.

Impact of Eradication Activities

Although NIDs have substantially decreased polio cases since 1993 (when 1803 cases were reported), the number of reported cases still remains high (Figure_1). In 1997, Pakistan reported 1147 polio cases; these cases represented widespread poliovirus circulation because poliovirus type 1 was identified in 86 (72%) of the 120 districts and poliovirus type 3 in 24 (20%) districts in 18 (75%) of Pakistan's 24 divisions (Figure_2). Poliovirus type 2 was isolated from two cases from NWFP in 1997. In addition to widespread endemic polio in 1997, four outbreaks of greater than 30 cases each occurred in four districts in NWFP and Balochistan, Pakistan.

Through November 1998, 277 polio cases reported in 1998 have been confirmed, a 74% decrease from the same period of 1997 (Figure_2). These cases occurred predominantly in children aged less than 3 years (83%) and in children who received less than three doses of routine or supplemental OPV (73%). In addition to substantial reduction in polio incidence, previous widespread transmission has been limited following the 1997-1998 NIDs to three main areas -- Karachi, southern Sindh (Hyderabad division), and central NWFP (Peshawar, Kohat, and Malakand divisions). Cases confirmed by wild poliovirus type 1 isolation have decreased by 75% from 1997 and were identified in 44 districts. Wild poliovirus type 3, however, has been found in 25 districts in 1998, with no decrease from 1997. No wild poliovirus type 2 has been isolated in 1998, and no outbreaks of greater than 20 cases had occurred as of November 1998.

Reported by: National Institutes of Health, Islamabad, Pakistan. Expanded Program on Immunization, Eastern Mediterranean Region, World Health Organization, Alexandria, Egypt. Vaccines and Other Biologicals, World Health Organization, Geneva, Switzerland. Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Vaccine-Preventable Disease Eradication Div, National Immunization Program; and an EIS Officer, CDC.

Editorial Note

Editorial Note: Laboratory and surveillance data suggest that after 4 years of eradication efforts in Pakistan, previous widespread poliovirus transmission has been reduced greatly, with sustained transmission limited to focal geographic areas. Polio cases have been reduced by 74% from 1997 to 1998, with an 88% decrease in the most populous province (Punjab). Wild poliovirus type 2 has not been isolated as of November 1998, and the number of poliovirus genotypes circulating in 1998 has been reduced (2). The reduced polio incidence in 1998 may be attributed to improved NIDs, cross-border vaccination activities, outbreak response vaccination, and immunity caused by previous widespread virus circulation.

Pakistan conducted five sets of NIDs before reaching the level of poliovirus control observed in 1998. Reasons for delayed impact of polio eradication activities may include conducting the first two sets of NIDs during the high poliovirus circulation season, nonuniform coverage for both NID and routine vaccination, and low routine OPV3 coverage. The Pakistan experience indicates that among densely populated countries with a warm climate and poor sanitation such as Pakistan, NIDs may have a rapid impact on polio incidence only in the presence of high routine vaccination (3).

Surveillance indicators suggest that case finding and investigation should be strengthened. Efforts to improve AFP surveillance will include hiring surveillance coordinators in each large province, monthly monitoring visits to each district, and inter-divisional meetings to review surveillance and provide additional training.

To eradicate polio from Pakistan, successful NIDs and other routine and supplementary vaccination activities should be continued and strengthened. Efforts to improve routine vaccination will include assuring a steady vaccine supply, expanding vaccine delivery to all primary health-care sites, and renewed training and social mobilization to ensure consumer demand for vaccination. Other supplementary vaccination activities, such as a third NID round or subnational NIDs in high-risk areas, will be necessary to assure rapid progress to meet the 2000 goal. Pakistan will expand supplemental vaccination activities in high-risk areas in spring 1999 to include all high-risk districts in Sindh, Balochistan, and NWFP. Strong support from the Pakistan government and international partners will be necessary to continue the substantial progress observed in 1998 **.

References

  1. CDC. Progress toward global eradication poliomyelitis,1997. MMWR 1998;47:414-9.
  2. CDC. Virologic surveillance and progress toward poliomyelitis eradication -- eastern mediterranean region, 1995-September 1998. MMWR 1998;47:1001-5.
  3. CDC. Progress toward poliomyelitis eradication -- People's Republic of China, 1990-1996. MMWR 1996;45:1076-9.

Mass campaigns held over a short period of time (days to weeks) in which two doses of oral poliovirus vaccine are administered to all children in the target group, regardless of prior vaccination history, with an interval of 4-6 weeks between doses. ** Polio eradication in Pakistan is supported by the governments of Pakistan, Japan, and the United Kingdom; WHO; United Nations Children's Fund (UNICEF), CDC, and Rotary International.



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Table_1
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TABLE 1. Number of acute flaccid paralysis (AFP) cases, poliomyelitis cases, and wild poliovirus serotypes, and AFP
surveillance indicators, by province and year -- Pakistan, 1997-1998
=========================================================================================================================================================
                                                                                                                 Surveillance indicators
                                                                                                   ----------------------------------------------------
                                  No. reported cases                                                                           % AFP          % AFP
                                -----------------------       No. wild poliovirus serotypes                                  cases with     cases with
                                              Confirmed       -----------------------------                       Nonpolio    adequate        60-day
Year      Province              Total AFP       polio*        P1+           P2           P3        AFP rate&     AFP rate&   specimens@     follow-up**
-------------------------------------------------------------------------------------------------------------------------------------------------------
1997      Punjab                    850          565          224            0           15            2.4          0.8           35             66
          Sindh                     361          272           86            0            5            2.4          0.6           41             78
          NWFP/FATA++               311          233          147            2            6            3.1          0.8           68             67
          Balochistan                96           73           25            0            3            2.7          0.7           43             54
          AJK&&                       2            1            0            0            0            0.1          0.1           50             50
          FANA@@                      4            3            2            0            0            1.0          0.3            0             25
          Islamabad                   0            0            3            0            0              0            0            0              0
          Total                    1624         1147          487            2           29            2.5          0.7           43             67

1998***   Punjab                    287           63           16            0            5            0.9          0.6           68             80
          Sindh                     290          147           58            0           13            2.2          0.8           51             81
          NWFP/FATA                  89           40           28            0           12            1.0          0.5           83             62
          Balochistan                42           22            8            0            3            1.4          0.6           43             41
          AJK                        11            1            0            0            0            0.8          0.8           55             45
          FANA                        4            4            1            0            0            1.0            0            0             75
          Islamabad                   0            0            1            0            0              0            0            0              0
          Total                     723          277          112            0           33            1.2          0.6           61             75
-------------------------------------------------------------------------------------------------------------------------------------------------------
  * Laboratory-confirmed or clinically (in the absence of adequate specimens) confirmed cases.
  + Isolates for 1997 are presumed wild: 205 (42%) were confirmed wild, 97% (205 of 212) of isolates were characterized as wild. Isolates
    for 1998 all were characterized, and numbers shown are confirmed wild.
  & Per 100,000 children aged <15 years.
  @ Two stool specimens collected 24 hours apart and within 14 days of onset of paralysis.
 ** Follow-up for residual paralysis 60-days after onset of paralysis; 1998 for cases with onset through October.
 ++ Northwest Frontier Province/Federally Administered Tribal Areas.
 && Azad Jammu Kashmi.
 @@ Federally Administered Northern Areas.
*** Data for cases with onset during January-November 1998.
=========================================================================================================================================================


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