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Progress Toward Poliomyelitis Eradication -- West Africa, 1997-September 1998
In 1988, the World Health Assembly adopted the goal of global eradication of poliomyelitis by 2000 (1). Although substantial progress has been reported in many parts of the world toward achieving this goal (2), West Africa remains a major reservoir of poliovirus transmission (3). This report summarizes progress achieved in the 15 countries of the World Health Organization (WHO) West African subregion (excluding Nigeria) during 1997-1998, reviews the implementation of polio eradication strategies, and suggests that, if activities are intensified and adequate resources are provided, achieving the eradication goal by the target date remains feasible.
Reported routine coverage with three doses of oral poliovirus vaccine (OPV3) among children aged less than 1 year remains low in most countries. In 1997, only three (Algeria, Benin, and The Gambia) of 15 countries reported that greater than 70% of children were vaccinated routinely with OPV3 (Table_1).
During January 1997-June 1998, all but two countries (Sierra Leone and Liberia) in the subregion administered supplementary OPV doses during National Immunization Days (NIDs) *. Efforts are under way to conduct NIDs in these two countries before the end of 1998. NIDs were held for the first time during January 1997-June 1998 in The Gambia, Guinea, Guinea-Bissau, Mali, Niger, and Senegal. Vaccination coverage in all countries was reported at greater than or equal to 80% for both rounds (Table_1).
As of September 1998, surveillance for acute flaccid paralysis (AFP) had not been established in The Gambia, Liberia, Mauritania, and Sierra Leone. During January-September 1998, 189 cases of AFP were reported in the West African subregion (Table_1); the nonpolio AFP rate for the subregion (an indicator of the sensitivity of the surveillance system) was 0.40 cases per 100,000 children aged less than 15 years (target: nonpolio AFP rate of greater than or equal to 1 per 100,000). Most countries reported nonpolio AFP rates of less than or equal to 0.30, except Algeria (0.66), Benin (0.43), Ghana (0.49), and Cote d'Ivoire (0.72). In 44% of AFP cases, two specimens were collected within 14 days of onset of paralysis. In all countries, the geographic distribution of reported AFP cases did not cover more than half of the country; cases were concentrated near the capital city and/or near the coast. In Ghana, 42% of AFP cases had stool specimens collected greater than 21 days after onset of paralysis, and 23% were collected greater than 28 days after onset. Almost none of reported AFP cases had a 60-day follow-up examination.
During January-September 1998, wild poliovirus type 1 was isolated from 15 AFP cases in Benin (one case), Burkina Faso (three), Ghana (three), Cote d'Ivoire (four), Niger (two), and Senegal (two) (Table_1). In Benin, Burkina Faso, Ghana, and Cote d'Ivoire, wild poliovirus type 1 was isolated after the second year of NIDs. Partial genomic sequence analysis of virus isolates from AFP cases with onset of paralysis in 1998 from Benin, Burkina Faso, Cote d'Ivoire, Ghana, and Niger indicates that transmission is still occurring within and between these countries. Sequence analysis indicates three different genotypes of wild poliovirus type 1 were isolated after the second NID round both in Ougadougou, Burkina Faso, and Abidjan, Cote d'Ivoire.
Reported by: Inter-Country Program, Expanded Program on Immunization, World Health Organization Sub-Regional Office for West Africa, Abidjan, Cote d'Ivoire. Expanded Program on Immunization, World Health Organization Regional Office for Africa, Harare, Zimbabwe. Global Program for Vaccines and Immunization, 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, CDC.
Editorial Note: In 1989, the WHO African Regional Committee adopted the global goal of eradicating poliomyelitis by 2000 (4), and polio eradication remains a high priority in the African Region. The countries of the Organization of African Unity (OAU) emphasized in the declaration of Yaounde, Cameroon, of July 1996 their determination to achieve this goal by implementing the WHO-recommended strategies. In August 1996, the WHO Regional Office launched the initiative "Kick Polio Out of Africa."
Substantial progress toward polio eradication has been made, although widespread transmission of poliovirus continues throughout western Africa because of 1) intense poliovirus transmission before the start of NIDs associated with very low routine OPV3 coverage rates, and 2) actual coverage rates lower than reported coverage rates with supplemental OPV doses during NIDs. Program reviews are planned to gain a better understanding of the factors associated with the continuing high level of wild poliovirus transmission.
The performance of AFP surveillance remains at low levels in most countries. There is a lack of rapid case investigation, collection of adequate stool specimens, and 60-day follow-up examination, limiting the probability that polio cases are confirmed based on isolation of wild poliovirus. High-quality AFP surveillance is essential to assess the impact of polio eradication strategies and, at later stages, to guide interventions aimed at interrupting transmission of wild poliovirus in the remaining virus reservoirs.
Emphasis should be placed on active surveillance at the provincial level to improve the completeness and timeliness of detection, reporting and investigation of AFP cases, and collection of adequate stool specimens. Additional personnel are needed immediately to conduct active surveillance, and additional provisions are required to support operational expenses, especially transportation at the provincial level.
A functional regional laboratory network has been established to provide rapid virus isolation, intratypic differentiation, and genomic sequencing. However, the usefulness of this network is limited by insufficient surveillance for AFP and limited collection of stool specimens.
Rapid success of polio eradication activities in West Africa is substantially constrained by relatively low levels of routine vaccination coverage in several countries. In some countries, it will not be possible to increase routine OPV3 coverage levels to at least 80% of the population aged less than 1 year by 2000. Additional vaccination rounds during NIDs are required in most areas to achieve the eradication goal.
The experience from the Americas and the Western Pacific Region indicates that poliovirus transmission can be interrupted even in the absence of high routine OPV3 coverage levels if comprehensive, high-quality vaccination campaigns, complemented by high quality AFP surveillance and "mopping-up" ** activities, are conducted (5). Financial support is committed for NIDs and surveillance; however, additional financial resources *** will be needed for additional vaccination rounds and "mopping-up."
Governments in the West African subregion are pursuing polio eradication vigorously, even though meningitis, measles, and other diseases are of higher immediate priority in many countries. The polio eradication initiative helps to build integrated surveillance systems and to develop strategies to extend routine vaccination services to previously unreached populations. Provided that additional resources are made available, countries of the subregions will be able to accelerate the initiative to ensure interruption of poliovirus transmission by 2000 (6).
* Mass campaigns over a short period (days to weeks) in which two doses of oral poliovirus vaccine are administered to all children in the target group (usually aged 0-4 years) regardless of previous vaccination history, with an interval of 4-6 weeks between doses.
** Focal mass campaigns in high-risk areas during a short period (days to weeks) in which two doses of OPV are administered during house-to-house visits to all children in the target age groups, regardless of previous vaccination history, with an interval of 4-6 weeks between doses.
*** The polio eradication initiative is supported by individual countries in which polio is endemic. In addition, external support for Africa is provided primarily by WHO; United Nations Children's Fund (UNICEF); the governments of Canada, Germany, Japan, United Kingdom, and United States (through USAID and CDC); and Rotary International.
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TABLE 1. Vaccination coverage with three doses of oral poliovirus vaccine (OPV3) and number of confirmed polio cases during 1997, vaccination coverage during National Immunization Days (NIDs)*, number of acute flaccid paralysis (AFP) cases, number of cases with wild virus isolated, and nonpolio AFP rates, January-September 1998 -- West African subregion =========================================================================================================================================== No. confirmed 1998 polio cases ------------------------------------------------------ for 1997 NIDs coverage+ No. nonpolio No. AFP Cases with 1997 OPV3 (wild virus ----------------------- AFP cases cases wild virus Nonpolio AFP Country coverage isolated cases) Round 1 Round 2 expected reported isolated rate& ---------------------------------------------------------------------------------------------------------------------------------------- Algeria 79% 0 92% 92% 120 59 0 0.66 Benin 71% 2 100% 100% 25 9 1 0.43 Burkina Faso 40% 3 ( 2) 100% 100% 45 13 3 0.30 Cote d'Ivoire 70% 3 ( 3) 100% NR@ 63 38 4 0.72 The Gambia 98% 0 NR NR 5 0 0 0** Ghana 61% 4 ( 2) 98% 102% 85 34 3 0.49 Guinea 53% 0 100% 100% 33 3 0 0.12 Guinea-Bissau 63% 0 NR NR 5 NR NR NR Liberia 45% NR NC++ NC 10 0 0 0** Mali 52% 0 95% 100% 45 10 0 0.30 Mauritania 28% 0 90% 93% 11 4 pending 0** Niger 28% 6 ( 5) 88% 95% 50 13 2 0.29 Senegal 65% 2 ( 1) 97% 100% 42 2 2 0 Sierra Leone 33% NR NC NC 20 1 0 0.07** Togo 40% 1 ( 1) 99% 100% 22 3 pending 0.10 Total 21 (14) 581 189 15 0.40 ---------------------------------------------------------------------------------------------------------------------------------------- * Mass campaigns over a short period (days to weeks) in which two doses of oral poliovirus vaccine are administered to all children in the target group (usually aged 0-4 years) regardless of previous vaccination history, with an interval of 4-6 weeks between doses. + January 1997-June 1998. & Annualized nonpolio AFP rate. @ Not reported. ** AFP surveillance system not yet established. ++ No NIDs conducted. ===========================================================================================================================================
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