Progress Toward Global Eradication of Poliomyelitis, 1996

Substantial progress was achieved during 1996 to further implement the World Health Organization (WHO)-recommended strategies for the global eradication of poliomyelitis (1). An international coalition of partners supporting the eradication effort in countries with endemic polio includes WHO, Rotary International, CDC, United Nations Children's Fund, and governments of countries with and without endemic polio. This report updates progress toward global polio eradication based on information available at WHO as of April 30, 1997. Progress in Implementing Strategies

Routine vaccination. Global coverage with three doses of oral poliovirus vaccine (OPV3) among infants aged less than 1 year in 1996 was 81% (compared with 83% in 1995). OPV3 coverage was greater than 80% in all WHO regions except the African Region (AFR). In AFR, coverage increased from 32% in 1988 to 58% in 1995 and to 60% in 1996.

Supplementary vaccination. In 1996, a total of 82 countries conducted National Immunization Days (NIDs) * (compared with 62 countries in 1995); since 1985, a cumulative total of 92 countries have conducted NIDs (Figure_1). Globally, during 1996, approximately 419 million children aged less than 5 years (approximately two thirds of the world's children aged less than 5 years) received oral poliovirus vaccine (OPV) during NIDs. By the end of 1996, all countries in Asia and Europe with endemic polio had conducted NIDs; globally, 17 countries with endemic polio had not conducted NIDs (15 of 42 countries in AFR with endemic polio and two of 23 countries with endemic polio in the Eastern Mediterranean Region {EMR}). In addition, four countries in AFR conducted Subnational Immunization Days in 1996 in preparation for NIDs in 1997.

To rapidly interrupt poliovirus transmission and ensure coverage of migrant populations in border areas, NIDs in 1996 were coordinated between countries and among WHO regions. "Operation MECACAR" synchronized NIDs among 18 countries of the European Region (EUR) and EMR and achieved vaccination coverage of 95% (58 million children) (2). NIDs conducted during December 1996 and January 1997 provided vaccination with OPV to 257 million children aged less than 5 years in Bangladesh, Bhutan, India, Myanmar, Nepal, Thailand (in the South East Asia Region {SEAR}), People's Republic of China, Vietnam (in the Western Pacific Region {WPR}), and Pakistan (in EMR). In India, the first round of NIDs in December 1996 achieved vaccination coverage of 117 million children aged less than 5 years, and the second round in January 1997 achieved vaccination coverage of 127 million children -- this round was the largest vaccination campaign ever conducted. NIDs were conducted in 27 countries in Africa during 1996 as part of the "Kick Polio out of Africa" campaign; this campaign targeted three fourths of children aged less than 5 years living in sub-Saharan Africa (approximately 74 million children) (3). In AFR, all countries with endemic polio except Democratic Republic of Congo (formerly Zaire) plan to conduct NIDs in 1997 (3).

Mopping-up vaccination. Targeted supplementary house-to-house vaccination activities ("mopping-up" campaigns) were conducted in high-risk areas (areas identified as potential or known foci of continued poliovirus transmission based on surveillance for acute flaccid paralysis {AFP}). During 1995-1996, mopping-up vaccination in Yunnan Province, China, targeted approximately 3 million children aged less than 5 years. This campaign focused primarily on counties bordering Myanmar; these counties were targeted because of the identification of four imported cases from Myanmar in persons who were excreting wild poliovirus.

AFP surveillance. AFP surveillance is now conducted in 126 (86%) of 146 countries where polio is or recently was endemic. From 1995 to 1996, the number of countries conducting AFP surveillance increased from 120 to 137 (including 11 countries in which polio is not endemic).

Two important performance indicators for AFP surveillance are

1. the annual rate of nonpolio AFP per 100,000 children aged less than 15 years (target: greater than 1 case per 100,000 population); and 2) the percentage of AFP cases for which adequate stool specimens have been collected (i.e., two stool specimens collected within 2 weeks of onset of paralysis {target: greater than or equal to 80%}). From 1995 to 1996, the global rate for nonpolio AFP increased from 0.4 to 0.6, although region-specific rates varied substantially (Table_1). Rates of nonpolio AFP were less than 0.1 in SEAR and AFR, where AFP surveillance systems are being established.

The proportion of countries that have implemented and achieved high quality AFP surveillance (defined as an AFP rate of greater than or equal to 1 per 100,000) also varied substantially by region. In the American Region (AMR), WPR, and SEAR, all countries where polio was or recently had been endemic conducted AFP surveillance; in AMR and WPR, 67% and 50%, respectively, of countries reported a rate of nonpolio AFP of greater than or equal to 1. AFP surveillance had not yet been established in 15 (36%) of the 42 countries in AFR, three (13%) of the 23 in EMR, and two (11%) of the 18 in EUR. In all regions except AMR and WPR, less than 25% of countries reported nonpolio AFP rates of greater than or equal to 1.

Laboratory network. In addition to the 16 regional and six specialized reference laboratories, the number of national laboratories participating in the Global Polio Laboratory Network increased from 65 in 1995 to 67 in 1996. In 1996, a process was initiated to formally accredit all national laboratories for participation in the WHO Poliomyelitis Eradication Program. Accreditation will ensure quality and facilitate the use of standardized procedures and reagents. Impact of Strategies on Polio Incidence

In 1996, a total of 3997 polio cases were reported globally, a decrease of 43% from the 7032 cases reported in 1995. In 1996, a total of 155 countries reported zero cases of polio (compared with 150 countries in 1995), 18 countries reported one to 10 cases (compared with 27 countries in 1995), and 27 countries reported greater than 10 cases (compared with 30 countries in 1995); the 14 countries that made no report primarily included small countries, island nations, and war-affected countries.

In AFR, the number of polio cases reported in 1996 decreased 13% from 1995 (from 2192 to 1898 cases). The impact of NIDs conducted during the 1996 "Kick Polio out of Africa" campaign on disease incidence can be evaluated in 1997. In AMR during 1996, no indigenous wild poliovirus was isolated for the fifth consecutive year, despite continuing high quality AFP surveillance and testing of adequate stool specimens obtained from 1485 (76%) of 1954 patients with AFP.

In EMR, the number of reported polio cases declined 53% from 1995 to 1996 (789 to 373), despite improvements in surveillance for AFP (Table_1). However, wild poliovirus continued to circulate in Pakistan and Egypt. In Egypt, endemic transmission continued with 99 virologically confirmed cases of polio (attributable to serotypes 1 and 3) in 18 (67%) of the 27 governorates; the 99 cases were an increase from the 71 cases reported in 1995. In Pakistan, although the number of polio cases decreased from 460 in 1995 to 223 in 1996, wild poliovirus was isolated from patients in all provinces in 1996.

The number of reported cases in EUR decreased from 1995 (210 cases) to 1996 (191 cases). However, 167 (87%) of the 191 cases in 1996 were associated with a large outbreak resulting from a wild poliovirus importation into Albania (138 cases with 16 deaths), Yugoslavia (Kosovo, 24 cases reported), and Greece (five cases reported). In countries participating in "Operation MECACAR" (2), the number of cases continued to decrease from 1995 (53) to 1996 (19).

The number of reported cases in SEAR decreased 67% from 1995 (3349) to 1996 (1116) (4), mainly reflecting the impact of NIDs in India conducted in December 1995 and January 1996. The number of cases reported in India decreased 69% from 1995 (3263) to 1996 (1005). High priorities in SEAR include rapid improvement of AFP surveillance to monitor the effect of NIDs and target future supplementary vaccination, and efforts are being initiated to strengthen AFP surveillance in six of eight countries in the region.

In WPR, 419 (8%) of 5288 AFP cases reported in 1996 were confirmed as polio (compared with 492 {9%} of 5650 cases in 1995). Of the 419 cases, 21 (5%) were confirmed based on wild poliovirus isolation, and three of the 21 were imported into southwestern China from Myanmar. No indigenous wild poliovirus was isolated in China during 1996. The other 18 wild-virus-associated polio cases were reported from Cambodia (15), Vietnam (two), and Laos (one). The areas in Cambodia and southern Vietnam in which viruses were found constitute the last known remaining reservoir of wild poliovirus transmission in WPR. During May-June 1997, a cross-border mopping-up operation was conducted in areas of Cambodia, Laos, and Vietnam to interrupt regional transmission.

Reported by: Global Program for Vaccines and Immunization, World Health Organization, Geneva, Switzerland. Respiratory and Enterovirus Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Polio Eradication Activity, National Immunization Program, CDC.

Editorial Note

Editorial Note: In 1996, progress toward the eradication of polio was aided by expanding the number of countries conducting NIDs, especially in AFR and SEAR; this expansion permitted the provision of supplemental doses of OPV to reach two thirds of all children aged less than 5 years worldwide. In addition, an increasing number of countries participated in multinational, synchronized NIDs to target the remaining foci of transmission of wild poliovirus. As a result of the efforts to expand supplementary vaccination activities, the number of reported polio cases rapidly decreased in many countries. Despite this progress, efforts to develop AFP surveillance -- including high-quality laboratory support -- have lagged, and the highest priorities now are to improve surveillance and conduct NIDs in the remaining countries with endemic polio. The rapid development of complete and timely AFP surveillance, particularly in the countries with endemic disease in the AFR, EMR, and SEAR, is an urgent priority to achieve the goal of global polio eradication by the year 2000. The global incidence of polio may decline further during 1997 as a result of the planned implementation of NIDs for the first time in all except one of the remaining countries with endemic polio.

War-affected or politically isolated countries (e.g., North Korea, Somalia, southern Sudan, and Democratic Republic of Congo) are reservoirs from which wild virus may continue spreading into bordering or distant polio-free countries, and intensification of the eradication initiative in these countries is critical to the achievement of global eradication. The polio outbreak involving Albania, Yugoslavia, and Greece underscored how countries previously polio-free may remain at risk for poliovirus importation because of suboptimal vaccination coverage or inadequate vaccination of subpopulations.

Although most of the resources to implement polio eradication have been provided by the countries with endemic polio, success of this initiative requires support from other sources, and international and interregional coordination. Projected resource requirements include approximately $175 million in external support to sustain polio eradication activities globally during 1997, and total external support of $1 billion for 1997-2005. External support also must continue for countries and regions where the incidence of polio has reached low levels to ensure interruption of the final chains of poliovirus transmission and to permit the eventual certification of eradication.

References

1. CDC. Progress toward global eradication of poliomyelitis, 1995. MMWR 1996;45:565-8.

2. CDC. Update: mass vaccination with oral poliovirus vaccine -- Asia and Europe, 1996. MMWR 1996;45:911-4.

3. CDC. Progress toward poliomyelitis eradication -- Africa, 1996. MMWR 1997;46:321-5.

4. CDC. Update: progress toward poliomyelitis eradication -- South East Asia Region, 1995-1997. MMWR 1997;46:468-73.

* Mass campaigns over a short period (days to weeks) in which two doses of OPV are administered to all children in the target age group, regardless of prior vaccination history, with an interval of 4-6 weeks between doses.

TABLE 1. Confirmed poliomyelitis cases and acute flaccid paralysis (AFP) surveillance performance indicators, by World Health Organization region, 1995 and 1996
=====================================================================================================================================================================
               Countries where polio
               is or recently was
               endemic, 1996
           ---------------------------   Nonpolio AFP rate *                                    No. confirmed polio cases        Percentage reduction
                       Implemented      ---------------------     % AFP cases with two stool   --------------------------         in confirmed cases
Region +    Total    AFP surveillance    1995           1996        specimens in 1996             1995           1996              from 1995 to 1996
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
AFR           42           27           <0.1            <0.1               NA &                   2192           1898                    13%
AMR           45 @         45            1.2             1.2               76%                       0              0                    --
EMR           23           20            0.5             0.7               65%                     789            373                    53%
EUR           18           16 **         0.2             0.7               63%                     210            191                     9%
SEAR           8            8           <0.1            <0.1               39% ++                 3349           1116                    67%
WPR           10           10            1.2             1.2               80%                     492            419                    15%
Total        146          137            0.4             0.6               --                     7032           3997                    43%
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
*  Number of cases of AFP (not attributed to polio) per 100,000 children aged <15 years.
+  The regions are African (AFR), American (AMR), Eastern Mediterranean (EMR), European (EUR), South East Asia (SEAR), and Western Pacific (WPR).
&  Not available.
@  The last case of polio attributed to wild poliovirus was detected in 1991.
** In addition, 11 countries in which polio is not endemic conducted AFP surveillance in EUR.
++ Percentage excludes India, for which these data are not available.
=====================================================================================================================================================================

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