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Progress Toward Poliomyelitis Eradication --- Southern Africa, 2001--March 2003
Since the 1988 World Health Assembly resolution to eradicate poliomyelitis globally, substantial progress has been made in all World Health Organization (WHO) regions, and three regions (Americas, European, and Western Pacific) are classified as polio-free (1,2). The African Region comprises four epidemiologic blocks (Central, Eastern, Southern, and Western). The Southern African block comprises 14 countries --- 10 on the mainland (Angola, Botswana, Lesotho, Malawi, Mozambique, Namibia, South Africa, Swaziland, Zambia, and Zimbabwe) and four in the Indian Ocean (Comoros, Madagascar, Mauritius, and Seychelles) --- with a combined total population in 2002 of approximately 120 million persons. This report summarizes polio eradication efforts in the Southern African block during January 2001--March 2003, which indicate the possible interruption of wild poliovirus (WPV) transmission and underscore the need to sustain polio eradication efforts.
During 2001, coverage with 3 doses of oral poliovirus vaccine (OPV) was estimated at >90% in two countries (Mauritius and Seychelles), at 80%--89% in four countries (Botswana, Lesotho, Malawi, and South Africa), and at 70%--79% in five countries (Comoros, Mozambique, Swaziland, Zambia, and Zimbabwe). Coverage was lowest (<70%) in three countries: Namibia (64%), Madagascar (58%), and Angola (44%) (3).
Supplementary Immunization Activities
During 1996--2000, all countries in the Southern African block conducted supplementary immunization activities (SIAs) with OPV during >2 years (Table 1). SIAs consisted of two rounds of National Immunization Days (NIDs)* in the winter (May--September), targeting children aged <59 months. Angola, Namibia, and Zambia continued annual NIDs through 2002 because of WPV transmission in Angola and cross-border transmission in western Zambia. After having discontinued NIDs for 3 years, Madagascar resumed conducting NIDs in 2002 after a polio outbreak caused by circulating vaccine-derived poliovirus (cVDPV).
During 2001--2002, SIA quality improved substantially through more detailed microplanning (i.e., planning at the district level), house-to-house vaccination, intensified supervision of house-to-house vaccination teams, and separate tallying of children who never had received OPV. During the first round of NIDs in Madagascar in September 2002, of the approximately 3.7 million children aged <5 years who were vaccinated, approximately 492,000 (15%) never had received OPV. Analysis of the distribution of these children enabled the Ministry of Health to determine which geographic areas to focus on to improve routine vaccination. In 2002, SIAs were coordinated among countries inside and outside the Southern African block, and NIDs in Angola and Namibia were synchronized with SIAs in the Democratic Republic of Congo and selected countries of the Central African block. Angola plans to conduct additional NIDs in June and August 2003.
Incidence of Polio
Countries of the Southern African block with the most recent isolation of WPV from acute flaccid paralysis (AFP) cases include Zambia (2002, two cases imported from Angola), Angola (2001, one case), Madagascar (1997, one case), and Namibia (1995, at least eight cases) (Tables 1 and 2). In the other countries of the Southern African block, WPV was last isolated in 1993 or earlier. In Madagascar, a polio outbreak related to cVDPV during 2001--2002 was detected and controlled after NIDs were conducted during September--October 2002 (4).
The goal of AFP surveillance is to detect circulating polioviruses and provide data for developing appropriate supplementary vaccination strategies. AFP surveillance quality is evaluated by two key indicators: sensitivity of reporting (target: nonpolio AFP rate of >1 case per 100,000 children aged <15 years) and completeness of specimen collection (target: two adequate stool specimens from >80% of persons with AFP). All countries of the Southern African block except Madagascar and Mozambique have achieved a level of AFP surveillance that allows use of virologic case classification criteria (i.e., annual adequate specimens collected from >60% of persons with AFP) (5). Madagascar, Mozambique, Namibia, and South Africa have not yet achieved certification-quality AFP surveillance (adequate specimens from >80% of persons with AFP) in any year (Table 2). Analysis of AFP performance indicators at the subnational level indicates considerable surveillance deficiencies at the provincial and district level. During January--March 2003, surveillance performance in Southern African block countries continued to improve, especially in Botswana, Mozambique, South Africa, and Swaziland. Performance decreased substantially in Angola (Table 2).
Regional Laboratory Network
The polio laboratory network in the Southern African block consists of four laboratories: one each in Madagascar, Zambia (which also serves Tanzania), Zimbabwe (which also serves Malawi), and South Africa (a regional reference laboratory that serves the remaining countries in the block and countries in other blocks). During 2002, network laboratories processed 2,114 samples from 1,088 persons with AFP with paralysis onset (South Africa, 571 cases; Zambia, 277 cases [including 144 samples from Tanzania]; Zimbabwe, 182 cases; and Madagascar, 58 cases). The nonpolio enterovirus (NPEV) isolation rate (target: >10% of stool specimens with NPEV isolation) serves as a combined indicator of specimen quality (i.e., quality of the reverse cold chain for specimen transport) and laboratory sensitivity. For the eight countries that reported an NPEV isolation rate, the rate ranged from 0 to 44%. Angola, Botswana, Mozambique, Namibia, and South Africa all reported NPEV isolation rates of >10%.
Certification and Laboratory Containment of Poliovirus
All countries in the Southern African block except Namibia have established National Polio Expert Committees (NPECs) comprising experts who make the final classification of AFP cases as confirmed polio, polio-compatible, or nonpolio AFP. All countries have National Committees for the Certification of Polio Eradication (NCCs) comprising independent experts who work closely with the African Regional Certification Commission (ARCC) to achieve the eventual polio-free certification of the region. Although NPECs exist in the majority of countries of the Southern African block, delays in AFP case classification have occurred, with large numbers of AFP cases pending final classification for approximately 6 months; as of December 2002, a total of 283 persons with AFP with paralysis onset during 2002 had not been classified. In 2002, a total of 13 AFP cases were classified as polio-compatible (nine from Angola and four from South Africa). No clusters of polio-compatible cases were found.
NCCs in all Southern African block countries have begun to submit annual country progress reports on polio eradication to the ARCC. After >3 years of certification-quality AFP surveillance without detecting WPV, Malawi is one of the first eight countries in the African Region selected by ARCC to begin submitting final national documentation toward eventual certification in 2003. Efforts toward the eventual laboratory containment of WPVs also have begun, with the designation of national task forces (NTFs) for laboratory containment in Angola, Botswana, Madagascar, Malawi, Namibia, South Africa, Swaziland, and Zimbabwe. Lesotho and Zambia are in the process of establishing NTFs.
Reported by: Inter-Country Program Office, World Health Organization; Regional Office for Africa, World Health Organization, Harare, Zimbabwe. 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.
Editorial Note. The last reported cases of polio confirmed with isolation of WPV in the Southern African block were observed in Zambia in February 2002. During January 2001--March 2003, WPV was isolated only in Angola and Zambia, and AFP surveillance quality improved in several countries, most notably in Angola, which had faced enormous challenges because of war (6). However, the decline in surveillance performance in Angola during January--March 2003 demonstrates the fragile nature of surveillance in this country, and steps have been taken to ensure that surveillance quality will rebound rapidly.
Although transmission of indigenous WPV in the Southern African block might have been interrupted, the possibility of ongoing transmission of WPV in the Southern African block cannot be excluded despite improved AFP surveillance in several countries (particularly Madagascar, Mozambique, and South Africa) and the absence of reports of AFP cases in many areas (particularly in eastern Angola).
AFP surveillance quality in all countries of the Southern African block should be improved to ensure that inadequate AFP surveillance does not delay eradication and the eventual polio-free certification of the African Region. During 2002, an external surveillance review, an important tool to assess both the organization and performance of surveillance, was conducted in Angola, and reviews are planned in 2003 for Madagascar, Mozambique, and South Africa. In addition, the country technical advisory group for Angola will convene in June to review the polio eradication initiative in this country, monitor the implementation of the recommendations resulting from the 2002 surveillance review, and offer advice on further strengthening of surveillance and the need for SIAs (7).
The formation of functional NPECs and NCCs in the majority of countries indicates that progress is being made toward achieving certification. However, further political commitment to accelerate the implementation of key polio-eradication strategies, including all aspects of AFP surveillance, is needed in all countries in the Southern African block, particularly those that have not yet achieved certification-quality surveillance.
Support for the polio eradication initiative in Southern Africa has been provided primarily by WHO member states, the Netherlands, the United States, the United Kingdom, Rotary International, and CDC. For polio eradication activities in these countries to be sustained until global certification is achieved, additional funding will be required. Through national Expanded Program on Immunization Interagency Coordination Committees, polio eradication partners should explore opportunities to raise funds from government and local partner agencies to support some activities. Strengthening polio eradication strategies in Southern Africa will prevent importation and circulation of polioviruses until global polio eradication is certified.
* Nationwide mass campaigns during a short period (days to weeks) in which 2 doses of OPV are administered to all children (usually aged <5 years), regardless of previous vaccination history, with an interval of 4--6 weeks between doses.
Two stool specimens collected at an interval of at least 24 hours apart, within 14 days of onset of paralysis, and adequately shipped to the laboratory.
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