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Progress Toward Poliomyelitis Eradication --- African Region, 1999--March 2000
In 1988, the World Health Assembly resolved to eradicate poliomyelitis globally by 2000 (1). The African Region (AFR) of the World Health Organization (WHO) began implementing polio eradication strategies in 1996, including National Immunization Days (NIDs*) and acute flaccid paralysis (AFP) surveillance (2,3). This report summarizes progress toward polio eradication in AFR during 1999--March 2000, and suggests that although substantial progress has been reported toward interrupting poliovirus transmission in eastern and southern Africa, poliovirus remains endemic in other African countries in west and central Africa, especially among those experiencing internal strife or civil war.
AFR includes 48 countries and territories and is divided geographically into five major epidemiologic blocks: eastern, western, southern, central, and countries in special situations. Reported regional coverage with three doses of oral poliovirus vaccine (OPV3) among children aged 1 year was approximately 55% in 1999 and has remained relatively stable since 1990. OPV3 coverage by country ranged from 65%--75% in the eastern and southern blocks, 50%--55% in the western block, and approximately 40% in the central block. Coverage was lower (approximately 30%) among countries in difficult circumstances (e.g., Angola, Democratic Republic of Congo [DR Congo], and Ethiopia).
From January 1999 through March 2000, two or more rounds of NIDs or Subnational Immunization Days (SNIDs) were conducted in all 35 (73%) countries and territories of the region where polio is either endemic (20 countries) or was considered endemic until recently (15). An estimated 133 million children received at least two supplemental doses of OPV during 1999, representing a 50% increase over the number of children reached in similar campaigns in 1998. NIDs coverage was reported to be >80% in all countries, with the exception of Sierra Leone (76%) and Congo Brazzaville (55%). Countries conducting SNIDs (predominantly eastern and southern block countries) reported coverage >80%.
To accelerate progress toward eradication, intensified NIDs were conducted in nine countries in the region (Angola, Benin, Chad, DR Congo, Guinea-Bissau, Liberia, Niger, Nigeria, and Sierra Leone) during 1999. Intensified NIDs consisted of either additional rounds or administering the vaccine house-to house. DR Congo conducted three rounds of NIDs during July--September 1999 and reported coverage rates of 81%, 91%, and 80% for the first, second, and third rounds, respectively (4). Nigeria targeted 13 million children residing in 15 (35%) of 37 states during April--May 1999; all OPV doses were administered in house-to-house vaccination campaigns. This effort reached 10%--40% more children in each state than had been reported from previous NID rounds (5). SNIDs also were conducted in the capitals of Central African Republic (Bangui) and Burkina Faso (Ouagadougou) in May and June 1999.
AFP surveillance improved rapidly in AFR during 1999; 4999 AFP cases were reported in 1999 compared with 1754 in 1998, an increase of nearly 200%. The nonpolio AFP rate more than doubled from 0.3 cases per 100,000 children aged <15 years in 1998 to 0.8 in 1999 (target: >1 nonpolio AFP case per 100,000 population aged <15 years) (Table 1). However, the proportion of AFP cases with two stool specimens collected within 14 days of onset of paralysis declined from 35% in 1998 to 31% in 1999. Of the 15 polio laboratories in the region, 13 were accredited during 1999, and all stool specimens were processed in accredited network laboratories.
Impact on poliovirus transmission
In 1999, wild poliovirus was isolated from 238 AFP case-patients residing in 16 AFR countries, mainly in central and western Africa and Angola (Figure 1). Angola experienced the largest polio outbreak ever recorded in Africa with 1093 cases and 89 deaths (6). Wild poliovirus circulation was detected in stool specimens from AFP cases in Nigeria (95), Angola (53), Chad (35), Liberia (11), Niger (10), Cotê d'Ivoire (nine), and Benin (eight). Wild poliovirus also was detected in Cameroon, Central African Republic, DR Congo, Ethiopia, Ghana, Guinea, Mali, Sierra Leone, and Togo. No wild poliovirus was detected in southern Africa.
Reported by: Expanded Program on Immunization, World Health Organization Regional Office for Africa, Harare, Zimbabwe; Vaccines and Biologicals Div, 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.
Intensified efforts to achieve polio eradication were implemented in the remaining countries of AFR where polio is endemic during 1999. Specific actions to improve the quality of supplemental vaccination campaigns (NIDs and SNIDs) included 1) intensified NIDs using the house-to-house strategy; 2) increased provision of technical assistance (e.g., logisticians, epidemiologists, and social mobilization experts); 3) dissemination of guidelines to achieve quality NIDs; and 4) synchronization of NIDs among countries having contiguous borders, including special cross-border coordination strategies. In addition, SNIDs were implemented in at least two countries, and special attention was given to improving the quality and geographic coverage of AFP surveillance.
Serious constraints to improving the quality and the geographic coverage of NIDs persisted in 1999. Wars, civil unrest, and political instability made it impossible to reach all unvaccinated children in certain countries during NIDs (Angola, Congo Brazzaville, DR Congo, Nigeria, and Sierra Leone). In October and November of 1999, the global shortfall in the OPV supply made it necessary to postpone NIDs in Burknia Faso, Chad, Ghana, Kenya, Niger, Sierra Leone, and Togo. In addition, some countries received OPV without vaccine vial monitors.
Although AFP surveillance has improved substantially from 1998 to 1999, further improvements are needed to increase the nonpolio AFP rate from 0.8 to the standard threshold of >1.0, indicating a sensitive surveillance system. The stool collection rate remains low in AFR. Although some of the decrease in the collection rate during 1998--1999 may be because not all cases associated with the 1999 Angola outbreak needed to be virologically confirmed, stool collection rates in the region did not increase in 1999.
Wild poliovirus is assumed to circulate in Sierra Leone and Congo Brazzaville, but surveillance was not operating for most of 1999 in these countries. In addition, the quality of surveillance is inadequate to determine whether wild poliovirus transmission continues in Madagascar, Malawi, and Mozambique. These three countries have low routine vaccination coverage and no longer conduct supplementary vaccination activities.
Efforts to improve the quality of AFP surveillance in 1999 and early 2000 include 1) increased funding for AFP surveillance; 2) expansion of active surveillance to the provincial level; and 3) provision of additional technical support for AFP surveillance through the Stop Transmission of Polio (STOP) Initiative in Chad, DR Congo, Ghana, Guinea, Kenya, Niger, Nigeria, and Uganda.
Although indigenous wild poliovirus is virtually absent in southern and eastern Africa and wild poliovirus circulation has declined to low levels in the some parts of west Africa, countries with intense circulation of wild poliovirus, including Angola, Chad, DR Congo, Ethiopia, Nigeria, and Sierra Leone, pose a risk for delaying global polio eradication. The remaining major challenges to polio eradication in AFR are 1) conducting high-quality supplemental vaccination activities and additional rounds and mopping-up activities where indicated, with emphasis on reaching previously unvaccinated children; 2) gaining access to all children in countries affected by conflict (e.g., Angola, Congo Brazzaville, DR Congo, and Sierra Leone); 3) assuring adequate quantities of potent OPV vaccines for routine and supplemental vaccination activities; 4) addressing basic routine EPI infrastructure in Angola, DR Congo, Liberia, Nigeria, and Sierra Leone; 5) filling the shortfall in funding for polio eradication in AFR; and 6) rapidly improving the quality of AFP surveillance.
* Nationwide 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 age group (usually aged <5 years), regardless of vaccination history, with an interval of 4--6 weeks between doses.
The polio eradication initiative in AFR is supported by AFR member countries. External funding is provided by Rotary International, United Nations Childrens' Fund, the governments of Canada, United States, United Kingdom, Norway, and Belgium, the United Nations Foundation, the Gates Foundation, the De Beers Corporation, WHO, and CDC.
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