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Progress Toward Poliomyelitis Eradication --- India, Bangladesh, and Nepal, January 2001--June 2002
Since the World Health Assembly resolved in May 1988 to eradicate poliomyelitis, the estimated incidence of polio has decreased >99%, and three World Health Organization (WHO) regions (American, Western Pacific, and European) have been certified polio free (1). Member countries of the South-East Asia Region (SEAR)* of WHO began accelerating polio eradication activities in 1994 and since then have made substantial progress toward that goal (2). By January 2001, indigenous wild poliovirus transmission in SEAR was limited to northern India, with ongoing poliovirus transmission posing a continuing threat to Bangladesh and Nepal. This report summarizes progress towards polio eradication in India, Bangladesh, and Nepal during January 2001--June 2002 and highlights the remaining challenges to eradicating polio in these countries.
According to official government estimates, 70% of infants aged <1 year in India, 66% in Bangladesh, and 92% in Nepal received 3 doses of oral poliovirus vaccine (OPV) during 2001. National aggregate data might not reflect substantial in-country variation and are not necessarily verified by accurate surveys.
Supplementary Immunization Activities
During 2001, National Immunization Days (NIDs) were conducted in India, Bangladesh, and Nepal (total estimated 2001 population: 1 billion, 129 million, and 24 million persons, respectively). During December 2001--March 2002, the three countries conducted two rounds of synchronized NIDs. Since 1999, these supplementary immunization activities (SIAs) have been intensified through house-to-house vaccination after 1 day of fixed-site activities. During 2001, in addition to NIDs, each country conducted Subnational Immunization Days (SNIDs)§ including 1) one round during October in four high-risk states in India and in parts of four other states coordinated with four bordering districts of Nepal, 2) a one-round multiantigen campaign during August for high-risk districts in Bangladesh targeting 15% of children aged <5 years, and 3) two rounds in Nepal during April--May in the Terai region bordering India and in the Kathmand Valley.
During 2001, in response to the detection of wild poliovirus in India, 17 mop-up¶ vaccination campaigns were conducted covering 48 million children aged <5 years. For 2002, a total of 61 mop-up campaigns are planned targeting 29 million children aged <5 years; as of June, 15 have been completed covering 9.8 million children aged <5 years. Selected high-risk districts in northern states of India conducted an additional two rounds of house-to-house vaccination as a pre-emptive measure during spring 2001 (covering 34 million children aged <5 years) and spring 2002 (covering 8.9 million children aged <5 years).
Acute Flaccid Paralysis Surveillance
Acute Flaccid Paralysis (AFP) surveillance in India, Bangladesh, and Nepal is facilitated through a network of surveillance medical officers (SMOs) who receive special training and are responsible for assisting the local health authorities in a defined area. As of June 2002, India had 239 SMOs, Bangladesh had 33, and Nepal had 14. This system has been supported in Bangladesh and Nepal by Stop Transmission of Polio (STOP) teams**.
Since 2000, India, Bangladesh, and Nepal have exceeded the WHO-established target for a nonpolio AFP rate indicative of sensitive surveillance (i.e., >1 per 100,000 population aged <15 years) and met the WHO target measure of timeliness and completeness of stool specimen collection (i.e., >80%) (Table). As of June 2002, a total of 10 Indian states (accounting for 15% [approximately 151 million persons] of the country's total population) had nonpolio AFP rates of <1 per 100,000 population aged <15 years. Six Indian states (accounting for 8% [approximately 80 million persons] of the country's population) had inadequate stool specimen collection rates (i.e., <80%). During 2001, the nonpolio enterovirus isolation rate (target: >10%), a marker of laboratory performance and the integrity of the reverse cold chain for specimens, was 10%--30% in different laboratories (total: eight laboratories) of India, 29% in Bangladesh, and 29% in Nepal.
Wild Poliovirus Incidence
Since the last wild poliovirus positive cases occurred in Bangladesh (August 2000) and Nepal (November 2000), India has been the only country in SEAR with indigenous transmission. India reported 265 wild poliovirus cases in 2000. Of the 268 cases reported in 2001, a total of 209 (78%) cases were type 1 (P1), 56 (21%) were type 3 (P3), and three (1%) were mixtures of P1 and P3. During January--June 2002, a total of 159 wild virus isolates were identified (131 [82%] P1 and 28 [18%] P3) (Figure) compared with 31 isolates reported during January--June 2001.
During 2000--2001, the number of circulating poliovirus genetic lineages decreased for P1 (from eight to three) and P3 (from four to three); all cases observed during 2001 were attributable to one of these six remaining lineages, and no new lineages were identified. Surveillance data indicate that two northern states, Uttar Pradesh (UP) and Bihar, are the remaining endemic foci responsible for continuing circulation in India. Although wild poliovirus was isolated from a total of 63 districts in 11 Indian states in 2001, the majority were reported from these two states: 216 (81%) cases in UP and 27 (10%) in Bihar. As of June 2002, of the 159 cases reported from 50 districts in eight states, 135 (85%) were reported from UP and nine (6%) from a small cluster in Bihar. In UP, a large outbreak related to a single P1 strain has spread to new areas in central and eastern UP; P3 lineages were detected only in western UP. All cases identified in the other six states belong to P1 lineages indigenous to UP and Bihar and are considered importations from these areas.
Reported by: Vaccines and Biologicals Dept, World Health Organization, Regional Office for South-East Asia, New Delhi, India. Vaccines and Biologicals Dept, World Health Organization, Geneva, Switzerland. Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Global Immunization Div, National Immunization Program, CDC.
Since January 2001, substantial progress has been made toward polio eradication in SEAR with indigenous circulation of poliovirus now limited to the northern Indian states of UP and Bihar. Two countries in which polio was endemic recently, Bangladesh and Nepal, have remained polio-free. Transmission of P2 appears to have been interrupted globally, with the last case occurring in UP in October 1999. The SMO network has played a vital role in the achievement and maintenance of high-quality AFP surveillance levels in all three countries.
Despite this progress, continuing transmission during 2002 in northern India poses a challenge. Circulation of P3 in 2002 has been restricted primarily to western UP. The geographic range of P1 circulation in Bihar has diminished since 2001; however, the spread of wild poliovirus to districts of UP without endemic transmission and to other states in India indicates the urgency of implementing SIAs with improved quality. The principal reasons for failure to vaccinate children during vaccination campaigns are 1) vaccination teams not identifying all eligible children, 2) poor or nonexistent supervision in many areas, and 3) poor participation of families in underserved communities. High population density, poor sanitation and hygiene, and low routine vaccination coverage in these areas greatly favor transmission of wild poliovirus, and high birth rates leave large cohorts of children unvaccinated.
The basic strategies of AFP surveillance and intensive OPV campaigns to supplement routine vaccination programs have been proven successful in eradicating polio in nearly all states of India, the other nine countries of SEAR, and other countries worldwide (3). To interrupt transmission in northern India, innovative measures are needed to increase community involvement and improve the quality of SIAs. On the basis of an analysis of standardized independent observer checklists and program management reviews, many new approaches were implemented in India during January 2001--June 2002. These included 1) deploying follow-up vaccinator teams to find and vaccinate children missed by primary teams; 2) increasing the number of SMOs working in high-risk districts; 3) changing the ratio of supervisors to vaccination teams from one to five during SIAs to one to three in selected high-risk areas; 4) creating a network of social mobilization persons at the district, block, and village levels to generate demand and promote acceptance of vaccination; 5) retraining vaccinators and supervisors to improve interpersonal communication skills; 6) forming a National Operations Group comprising the Ministry of Health and national and international partners to facilitate rapid implementation of strategic decisions; and 7) increasing the number of field monitors and more extensive analysis of quality indicators.
India will continue to monitor the impact of these interventions during SNIDs that are planned to cover UP, Bihar, and parts of five other high-risk states during September and November 2002. In response to the detection of polio cases in border districts of India, Bangladesh and Nepal are intensifying AFP surveillance and SIAs in addition to ensuring high routine OPV3 coverage in these areas. Bangladesh expanded its SNIDs during August--September 2002 to include all districts neighboring India. Nepal is planning an aggressive OPV campaign in the border area with India during October--November 2002. The transmission of poliovirus in border districts highlights the importance of maintaining close communication and cooperation across borders to minimize the risk for re-introduction of wild poliovirus to areas that have interrupted transmission.
Progress towards polio eradication in India, Bangladesh, and Nepal is the result of substantial investments made by these countries and the international polio eradication partnership. The eradication initiative in SEAR is close to achieving its goal, and all groups involved should intensify their efforts to ensure success. This will require continuing political commitment and effective acceleration of strategies to reach every child during the planned immunization rounds, particularly in northern India.
*Bangladesh, Bhutan, Democratic People's Republic of Korea, India, Indonesia, Maldives, Myanmar, Nepal, Sri Lanka, and Thailand.
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