Impact of strategies on poliomyelitis incidence

As of mid-May 1998, 4116 poliomyelitis cases with onset during 1997 were reported worldwide. 1997 data are not yet complete, mainly as a result of incomplete and delayed reporting from Africa. While the 1997 total new exceeds the number of cases confirmed in 1996 (4074), a direct comparison is difficult because acute flaccid paralysis (AFP) reporting has improved significantly in 1997. Compared with 1998, when the global eradication goal was established, the number of reported cases has been reduced by 89% Beyond a simple decline in the number of poliomyelitis cases reported, the transmission of wild poliovirus is being interrupted in an increasing number of areas of the world.

The Region of the Americas was certified as poliomyelitis-free in 1994, and remains poliomyelitis-free, although the quality of AFP surveillance has slightly deteriorated in several formerly endemic countries.

The impact of supplementary immunisation in the African Region and the resulting change in incidence from 1996 to 1997, is difficult to measure because 1997 surveillance data from the Region is incomplete. Available surveillance data suggests that two poliovirus reservoirs remain: One in central Africa (mainly in the Democratic Republic of the Congo) and one in western Africa (mainly in Nigeria). Wild poliovirus was not isolated in southern and eastern Africa during 1997, however, even in the larger countries reporting relatively higher rates of non-poliomyelitis, AFP (eg Ghana, Namibia and Zimbabwe), surveillance is not geographically representative and the percentages of AFP cases with adequate stool specimens remains low.

Reported poliomyelitis cases increased from 532 in 1996 to 1023 in 1997 in the Eastern Mediterranean Region, primarily as a result of improved surveillance and outbreaks in Pakistan where all three serotypes of poliovirus continue to circulate and are detected. Reported cases decreased from 100 in 1996 to 14 in 1997 in Egypt despite improvements in surveillance (AFP rate of 0.84, 72% with adequate specimens). Poliovirus type 1 was the only serotype detected in 1997 in Egypt (both serotypes 1 and 3 were isolated in 1996). Afghanistan established AFP surveillance in early 1997, and all three poliomyelitis serotypes have already been identified.

Seven poliomyelitis cases were confirmed in the European Region in 1997, a decrease from 193 cases in 1996, when a large outbreak occurred in Albania and Yugoslavia. Except for one clinically-confirmed case in isolation. They were confined to south-eastern Turkey. Another area of concern for the European Region is Central Asia, with a continued risk of wild virus importation from South Asia (Afghanistan, Pakistan) and the low quality of AFP surveillance in Tajikistan, Turkmenistan and Uzbekistan.

Reported poliomyelitis cases increased from 1 203 in 1996 to 2 858 in 1997 in the South-East Asian region, primarily reflecting the improvements in surveillance in India as well a large outbreak of 751 cases in the Indian State of Uttar Pradesh. The completeness of AFP reporting improved in most other countries in the region, resulting in increases in the number of clinically-confirmed cases from 1996 to 1997 in Bangladesh (97 to 199), India (1005 to 2074) Indonesia (77 to 507), Myanmar (8 to 55) and Thailand (1 to 19). Wild polio viruses were isolated from 4 countries in the Region in 1997 (Bangladesh, India, Nepal and Thailand).

Nine cases of virologically-confirmed poliomyelitis cases were reported from the Western Pacific Region in 1997, all of which were reported from the Mekong river area of Cambodia and Vietnam. The last case reported from the Western Pacific Region occurred near Phnom Penh in Cambodia in March 1997.

Editorial Note
Since 1988, when the goal of global poliomyelitis eradication was adopted, substantial progress has been reported from all 6 WHO Regions. This progress accelerated in 1997 when National Immunisation days (NIDs) reached two-thirds of the word's children under 5 years of age, 35 national poliomyelitis laboratories were accredited by WHO, sensitive surveillance systems for poliomyelitis cases and poliovirus were established in virtually every poliomyelitis-endemic country, including those that experience civil war (eg Afghanistan), extensive mopping-up campaigns were conducted in the Mekong river region, and the "Kick polio out of Africa" campaign expanded further.

Surveillance is just beginning in many African countries; few AFP cases are identified and few stool specimens are collected and analyzed in network laboratories. Only 13 laboratories in the African laboratory network serve 31 countries, which requires frequent specimen transport between neighbouring countries. Limited laboratory capacity in Africa will also be challenged by much larger numbers of specimens as AFP surveillance improves.

AFP surveillance is critical to assessing the degree to which NIDs are reducing poliovirus circulation and to identify the remaining virus reservoirs. Because several years may be required to achieve adequate AFP surveillance, and since greater levels of support will be necessary for African countries, resources to build surveillance capacity in Africa must be secured urgently.

Poliovirus transmission now occurs primarily in South Asia and Sub-Saharan Africa, and transmission is most intense in the most populated countries (Bangladesh, India and Pakistan in Asia, the Democratic Republic of the Congo, Nigeria and Ethiopia in Africa). With the exception of the Democratic Republic of the Congo, all of these countries have initiated NIDs and have reduced poliovirus transmission. Nevertheless, poliovirus type 2 wild virus was detected in only one African country in 1997, and virological surveillance in this region is still not sufficient to document with confidence the absence of this virus serotype in much of Sub-Saharan Africa. Continuing circulation of poliovirus in the large remaining endemic countries must be stopped rapidly, not only because of the risk of exporting the virus into neighbouring countries and across continents, potentially re-seeding previously poliomyelitis-free areas with poliovirus.

Current or recent conflicts in Afghanistan, the Congo, Sudan and Tajikistan compound the difficulties of conducting NIDs and implementing AFP surveillance. The 4 poliomyelitis-endemic countries that have not conducted NIDs - the Democratic Republic of the Congo, Liberia, Sierra Leone, Somalia - are all affected by recent or ongoing conflicts. Interrupting poliovirus transmission in countries affected by conflict is a major concern for the initiative.

The costs of poliomyelitis eradication are shared by poliomyelitis-endemic countries and the international community. Individual countries provided approximately 80% of the total cost for poliomyelitis eradication in the Americas, and China and Indonesia contributed an even higher national share. However, in the poorest and least developed countries, the majority of cost to implement poliomyelitis eradication will need to come from external funding. WHO has estimated that more than 1 billion dollar in external funding, mainly for operational costs of NIDs, vaccine and surveillance, will be required globally for poliomyelitis eradication from 1998 to 2005; two-thirds of these funds are needed during the period 1998-2000.

Rapid progress towards global poliomyelitis eradication has led to the certification of poliomyelitis eradication in the Americas, the probable interruption of poliovirus transmission in the Western Pacific Region, the restriction of poliomyelitis transmission to a single area in the European Region, and the strengthening of national immunisation programmes around the world. However, global eradication requires that poliovirus transmission ceases everywhere. Less than 1 000 days remain to reach the year 2000 target. Success will depend on securing the additional resources to conduct and maintain eradication strategies in the remaining poliomyelitis-endemic countries, as well as on sustained political commitment in both non-endemic and endemic nations.

The eradication initiative continues to be supported by an international coalition of partners, including Rotary International, the US Government through the Centers for Disease Control and Prevention and USAID, UNICEF, WHO, Japan through JICA, Great Britain through DFID, Denmark through DANIDA, Germany through KfW, as well as the governments of many polio-endemic and non-endemic countries.

Reproduced from and with acknowledgement to the WHO Weekly Epidemiological Record 1998: 73; 161-168.