Current status of the global eradication of poliomyelitis / Rudolf H. Tangermann ...[et al.]

Current status of the global eradication of poliomyelitis Rudolf H. Tangermanna, Bruce Aylwarda, Maureen Birminghama, Rachel Hornerb, Jean-Marc 0/ivea, Benjamin M. Nkowanea, Harry F. Hui/a & Anthony Burtonc Substantial progress towards the global eradication of poliomyelitis by the year 2000 has been achieved since May 1988 when WHO Member States adopt- ed this goal at the Forty-first World Health Assem- bly. Virtually all polio-endemic countries have now begun to implement the WHO-recommended strategies to eradicate polio ( 1 ). This article de- scribes the scientific basis of the strategies used, the current degree of strategy implementation, and the status of polio eradication in the world. Polio eradication strategies and their implementation The WHO-recommended strategics for polio erad- ication are as follows: ( a) high routine immuniza- tion coverage with at least 3 doses of oral polio vaccine(> 80% OPV3); (b) annual National Immu- nization Days (NIDs), during which 2 supplemen- tal OPV doses are given to all children < 5 years; (c) laboratory-based surveillance for all cases of acute flaccid paralysis (AFP) in children under 15 years of age, with the collection and virological examination of stool specimens from every case, and (d) 'mopping-up' immunization campaigns to administer supplemental OPV doses through house-to-house campaigns in areas with persisting transmission of wild poliovirus. Routine immunization coverage Reaching and maintaining the highest routine im- munization coverage with OPV at all administrative levels remains the foundation on which the polio eradication initiative is built. In temperate, indus- trialized countries, high levels of seroconversion and interruption of poliovirus transmission have been attained with 3 doses of OPV in the routine immunization programme (2). Although high rou- tine OPV3 coverage has resulted in high levels of control in many tropical developing countries, wild virus transmission has often persisted owing to a number of factors which affect both the intensity a Medical Officer, Expanded Programme on Immunization, Global Programme for Vaccines and Immunization, World Health Organization, Gene\.!. b Statistical Assistant, Expanded Programme on Immunization, Global Programme for Vaccines and Immunization, World Health Organization, Geneva. c Systems Analyst, Expanded Programme on Immunization, Global Programme for Vaccines and Immunization, World Health Organization, Geneva. 188 of transmission (low sanitation levels, high popula- tion density) and seroconversion rates (high ma- ternal antibody, competing enterovirus infections, diarrhoea) (3). For these reasons, high routine cov- erage often only reduces transmission to low levels, requiring supplemental doses of OPV to interrupt transmission. At the start of the polio eradication initiative in 1988, global coverage with 3 doses ofOPV (OPV3) was 67% (Table ]), as compared to less than 10% in 1974. OPV3 coverage peaked in 1990 at 85%, stabi- lized near 80% in the first half of the 1990s and was 81 % in 1996. OPV3 coverage in 1996 was lowest in the African Region, but doubled in that Region from 32% in 1988 to 60% in 1996. National Immunization Days (N/Ds) Immunization strategies for global polio eradica- tion in endemic countries are based on the work of Chumakov (4) and others who first used mass im- munization campaig;ns to control polio epidemics in Hungary (5) and the former USSR. Based on refinements of this strategy in Cuba and Brazil (6), the Pan American Health Organization recom- mended National Immunization Days (NIDs) for polio eradication in endemic countries in the Fig.1 Cumulative number of countries conducting NIDs Nombre cumulatif de pays ayant organise des journees nationales de vaccination (JNV) 120 "' :i 100 Q) -c e 80 ..0 E 0 z I "' 60 Q) E c: ::, 0 (.J 40 0 ~ Q) ..0 E 20 ::, z 0 • NI Ds to be conducted .JNV prtivues 1~1~1~1~1m1m1~1~1~1m Year-Annee Data as of 24 June 1997 - Donnees au 24 juin 1997 Rapp. trimest. statist. sanit. mond., 50 (1997) Table 1 Reported poliomyelitis cases and oral polio vaccine (OPV) coverage 1988 and 1996, and acute flaccid paralysis (AFP) surveillance performance indicators 1996, by WHO Region Tableau 1 Cas de poliomyelite notifies et couverture par le vaccin antipoliomyelitique buccal (VPO), 1988 et 1996, et indicateurs d'efficacite de la surveillance de la paralysie flasque aigue (PFA), 1996, par Region OMS WHO Region- No. of reported % OPV3 coverage - AFP surveillance quality 1996 - Region OMS polio cases - reduction Couverture VP03 Oualite de la surveillance de la PFA 1996 Nombre de cas 1988-1996 de poliomyelite notifies 1988 1996 1988 1996 Non-polio AFP rate• - % AFP with 2 stool Taux de PFA specimens - % de cas non poliomyelitique• de PFA pour lesquels l'on dispose de 2 echantillons de selles Africa - Afrique 4 563 2 071 55% 32% 60% <0.1 NA America - Les Ameriques 308 0 100% 85% 88% 1.2 76% South-East Asia - Asie du Sud-Est 25 741 1125 96% 66% 84% < 0.1 39%b Eastern Mediterranean - Mediterranee orientale 2 339 528 77% 67% 78% 0.7 65% Europe 204 193 5% 60% 92% 0.7 63% Western Pacific - Pacifique occidental 2126 194 91% 85% 88% 1.2 80% Global - Niveau mondial 35 251 4 111 88% 67% 81% 0.6 a Number of AFP cases (not attributed to polio) per 100 OOO children aged <15 years. -Nombre de cas de PFA (non attribues a la poliomyelite) pour 100 OOO enfants ages de mains de 15 ans. b Percentage excludes India, for which these data are not available. - Ce pourcentage exclut l'lnde, pays pour lequel ces donnees ne sont pas disponibles. Americas. The effectiveness and global applicabil- ity of the NIDs strategy was further established through experience in China and other countries (7, 8). NIDs are conducted during the season of low poliovirus transmission in 2 rounds, 4 to 6 weeks apart. During each round, OPV is administered to all children <5 years of age, regardless of prior immunization status. NIDs interrupt poliovirus cir- culation by rapidly increasing systemic and intesti- nal immunity in the population, thereby limiting spread of the virus (1, 9, JO). The number of countries conducting NIDs worldwide has risen since the early 1990s, as the polio eradication initiative became operational in WHO regions (11). By the end of 1996, a cumula- tive total of 97 countries had conducted NIDs or Sub-NIDs (see Fig. 1), including all polio-endemic countries in the Americas, Asia and Europe, and 25 of 42 endemic countries in the African Region (14). Globally, 419 million children< 5 years were immunized during NIDs in 1996, approximately two-thirds of the world's children in that age group. In India, 127 million children< 5 years were immunized during the second round of 1996 NIDs, making this the largest single immunization campaign in history (12). Increasingly, NIDs are being coordinated be- tween countries and WHO regions to rapidly inter- rupt poliovirus transmission and ensure coverage of Wld hlth statist. quart., 50 (1997) migrant populations in border areas. Between De- cember 1996 and January 1997, 257 million chil- dren were immunized during NIDs in 11 countries of the Eastern Mediterranean, South-East Asian and Western Pacific regions of WHO. "Operation MECACAR" (13), conducted in 1995, 1996 and 1997, synchronized NIDs among 18 countries of the European and the Eastern Mediterranean regions, achieving immunization coverage of95%. Surveillance for acute flaccid paralysis (AFP) The goals of the surveillance strategy for polio eradication are to monitor progress, identify re- maining areas of wild virus transmission for 'mop- ping-up' immunization, and eventually provide the basis for certification of eradication. To achieve these goals, two stool specimens are collected from all AFP cases in children< 15 years and examined for the presence of wild poliovirus. Sun:eillance for cases of AFP, instead of clinical polio, increases the sensitivity of the surveillance system to detect polio cases, because clinical crite- ria alone are not sufficient to diagnose polio reli- ably. Atypical presentations of paralytic polio may be mistaken clinically for Guillain-Barre syndrome, transverse myelitis, or other paralytic conditions (15), and vice versa. For reporting purposes, the following AFP case definition is used: "All children < 15 years of age with acute flaccid paralysis, includ- 189 ing those considered to have Guillain-Barre syn- drome, and persons of any age in whom polio is suspected". The most important indicators for the quality of AFP surveillance are the annual rate of non-polio AFP cases in children< 15 years, and the percent- age of AFP cases from whom 2 specimens were collected within 2 weeks of paralysis onset ('ade- quate specimens'), since viral shedding is most intense during the first 2 weeks after onset. For effective AFP surveillance, the non-polio AFP rate should be at least 1 case per 100 OOO children< 15 ( 16) and at least 80% of AFP cases should have adequate specimens taken. A global network of polio laboratories has been developed, which is capable of detecting wild po- liovirus when and where it occurs. The laboratory network currently consists of 67 national laborato- ries, 16 regional reference laboratories, and 6 spe- cialized reference laboratories ( 17). National labo- ratories perform primary virus isolation, referring any polioviruses detected to regional reference lab- oratories where tests are performed to differentiate vaccine strains from wild virus strains. Specialized laboratories perform genomic sequencing studies on poliovirus isolates to determine the exact geo- graphical and temporal origin of a particular virus. A process of formal accreditation of national labo- ratories began in 1996 to ensure quality and facili- tate the use of standardized procedures and re- agents. By the end of 1996, AFP surveillance was being conducted in 126 (86%) of 146 countries where polio is or recently was endemic (11). In 1996, the global rate for non-polio AFP was at 0.6/ 100 OOO, although rates varied substantially by WHO region (see Tab/,e 1). Rates of non-polio AFP were still< 0.1 in the South-East Asian and African Regions, where AFP surveillance is just being established. The proportion of AFP cases with adequate speci- mens shows similar variation (see Tab/,e 1). Mopping-up immunization Despite NIDs, small foci of circulation of wild polioviruses often continue to persist. Continued transmission in these areas is often facilitated by high population density, poor sanitation levels and the presence of children missed by both rou- tine and supplementary immunization. Good sur- veillance is essential to identify these final reser- voirs of wild virus infection. Intensive, localized immunization campaigns, also known as 'mop- ping-up' campaigns, are required in these areas. In contrast to the strategy of immunizing at fixed posts as in NIDs, mopping-up must be done on a house-to-house basis to ensure that every single child in the area is found and immunized ( 1 ). Mopping-up immunization was first used during polio eradication in the Americas to target the last remaining foci of wild-virus transmission (18). 190 Experience has shown that mopping-up opera- tions are most effective if planned well ahead of time and conducted during the low-transmission phase. Large mopping-up immunization cam- paigns targeted the last remaining foci of trans- mission in 199 coastal counties of Colombia (19) in 1991 (850 OOO children immunized), and in 13 coastal departments of Peru in 1992 (20) (1.9 million children immunized). Mopping-up campaigns have also been con- ducted in the Western Pacific Region of WHO. During 1995-1996, approximately 3 million chil- dren < 5 years were immunized in border counties ofYunnan province, China, where 4 paralytic polio cases imported from Myanmar had been identi- fied. Another large mopping-up campaign was conducted in May:June 1997 in the Mekong river areas of Viet Nam and Cambodia, targeting mainly the migrant population living on boats. A total of 2 million children were immunized. Mopping-up campaigns are more intense and require even more resources than NIDs on a per- capita basis. Immunizing about one-third of Cambodia's target population< 5 years during the recent mopping-up was as costly as the full NID earlier in the year. Certification of polio eradication The process for certification of polio eradication has been established in each WHO region and at the global level. In 1994, the International Com- mission for Certification of Poliomyelitis Eradica- tion (ICCPE) certified that indigenous wild polio- viruses had been eradicated from the Region of the Americas (21). Despite continuing high quality AFP surveillance, indigenous wild poliovirus has not been isolated in the Region since September 1991. The Global Commission for the Certifica- tion of the Eradication of Poliomyelitis was set up in 1995 and has met twice since (1995, 1997). The Global Commission stated that WHO regions will only be certified as poliomyelitis-free after all countries and areas of the region have met the following criteria<l: (a) absence of circulation of indigenous wild polioviruses for at least a 3-year period in which surveillance activities have been maintained at the levels of performance needed for certification; (b) a national certification com- mittee in each country has validated and submit- ted the documentation required by the regional commission; and (i:) appropriate measures are in place to detect and respond to any importations of wild poliovirus. Regional commissions have now been appointed in all 5 other WHO regions where they ,vill oversee the certification process, aided by d Report of the first meeting of the Global Commifsion f &r the urtification of the Eradication of Poliomyelitis, WHO, Geneva, 1995 (Document \VHO/EPI/GEN/93.6). Rapp. trimest. statist. sanit. mond., 50 (1997) national certification committees in all countries. Regional certification will be based on detailed documentation of surveillance and immunization activities to be submitted by each country. The polio eradication coalition To achieve polio eradication, a global partnership was formed involving, among others, Rotary Inter- national, the United Nations Children's Fund (UNICEF), WHO, the Centers for Disease Control and Prevention (CDC), other donor governments, non-governmental organizations, and ministries of health in the polio-endemic countries. AUSAID, DANIDA, JICA and USAID have made significant contributions. Over the past decade, these partner agencies have provided funding as well as technical expertise, advocacy support and volunteers. Sup- port from Rotary International has been crucial for the initiative. Rotary continues to play an impor- tant advocacy role, it has funded the procurement of large quantities of oral polio vaccine and in- creasingly supports surveillance activities. In many countries, Rotary volunteers are directly involved in planning and implementing NIDs and surveil- lance activities. UNICEF facilitated the procure- ment of more than 700 million doses of OPV for NIDs in 1996, and also played a key role in negoti- ating a series of cease-fires in conflict zones to allow the immunization of children. The CDC provides funds for vaccine as well as a wide range of techni- ea! expertise, particularly to develop surveillance systems for AFP and wild poliovirus. Although substantial funding for polio eradica- tion has been provided by donor governments and other agencies, many polio-endemic countries underwrite most of the cost of polio eradication activities themselves: for example, it was estimated that over 80% of polio eradication costs in the Americas were met by individual countries, and in China, outside funding was used for less than 10% of NID costs. In the poorest countries (i.e., sub- Saharan Africa), however, external support is needed for more than 80% of polio eradication costs. Significant external funding, as well as inter- national and interregional cooperation, need to continue to achieve success. Projected resource requirements include approximately US$ 175 mil- lion in external support to sustain polio eradica- tion activities globally during 1997, and US$ 1 bil- lion for the period 1997-2005 ( 11 ). Impact on polio incidence Polio has been eradicated from the western hemi- sphere (WHO Region of the Americas) for more than 5 years (22). The last case of polio caused by wild poliovirus in South America was in a 2-year old Peruvian boy paralyzed in August 1991. The West- ern Pacific Region is close to eradication (23), with only one known remaining reservoir of wild virus circulation in the Mekong area of Cambodia and Map 1 Global reported incidence of indigenous poliomyelitis, 1995a Carte 1 Incidence de la poliomyelite autochtone notifiee au niveau mondial, 1995a D No report - Pas de notification - More than 10 cases - Plus de 10 cas B 1-10 cases - 1-10 cas HfiiWh! O cases - O cas a 4 111 polio cases reported as of 25 August 1997. - 4 111 cas de poliomyelite notifies au 25 aout 1997. Wld hlth statist. quart., 50 (1997) D 0 0 0 0 WHO 97496 191 the Southern Region of Viet Nam. Global polio incidence has decreased in recent years due to the implementation of NIDs. In 1996, a total of 4 111 polio cases were reported globally ( data as of 4 August 1997), a decrease of 88 % from the 35 251 cases reported in 1988 (Tab!.IJ I, Map I). In the African Region, 1996 was the first year in which a significant number of NIDs were con- ducted as part of the "Kick Polio out of Africa" campaign. The impact of these NIDs on polio inci- dence should be evident in 1997. Despite improvements in surveillance, the number of polio cases reported from the Eastern Mediterranean Region declined 77% from 1988 to 1996 (2 339 to 528). However, wild poliovirus con- tinues to circulate in Pakistan and Egypt. A recent polio outbreak, after the 1997 NIDs, was reported from the North-West Frontier Province in Pakistan in May/June 1997. In 1988, 204 polio cases were reported from 5 countries of the European Region; this included reported polio cases from 11 of 15 Republics of the former USSR. Several polio outbreaks occurred during the early 1990s following the break-up of the USSR, mainly in the Caucasus area and the Central Asian Republics. Of the 193 cases reported in the European Region in 1996, 167 were associ- ated with a large outbreak which resulted from a wild poliovirus importation into Albania (24). The outbreak primarily affected Albania, but also spread into Greece and the neighbouring Kosovo Region. The number of cases reported from coun- tries in the European Region participating in Op- eration ME CA CAR ( 13) decreased from 53 in 1995 to 19 in 1996. In the South-East Asia Region, the number of reported cases declined from 25 711 in 1988 to 1 125 in 1996, a 96% decrease. The rapid improve- ment of AFP surveillance now has highest priority for polio eradication in this region, particularly in those 6 countries in which AFP surveillance has recently been initiated. In the Western Pacific Region, confirmed polio cases declined by 91 % between 1988 (2 126) and 1996 ( 194). Of the 194 cases reported in 1996, only 21 ( 11 % ) were confirmed, based on wild poliovirus isolation, and no indigenous wild poliovirus was isolated in China during 1996. Conclusions There has been remarkable progress since the polio eradication goal was established in 1988, with an 88% decrease in the number of reported cases globally. By the end of 1997 it is expected that virtually all endemic countries in the world will have conducted full National Immunization Days, providing supplemental OPV to almost two-thirds of all children < 5 years globally. An increasing number of countries participate in multinational, synchronized NIDs to target the remaining foci of 192 transmission most effectively. As a result of in- creased supplementary immunization activities, the number of reported polio cases rapidly de- creased in many countries. Surveillance data indi- cate that the first NIDs in India, which until recent- ly contributed the largest number of reported cases annually, had a significant impact on polio inci- dence. By comparison, efforts to develop AFP surveil- lance have lagged behind. The rapid development of complete and timely AFP surveillance and con- tinuation of effective NIDs, particularly in the re- maining countries with endemic polio in the Afri- can, South-East Asian and Eastern Mediterranean regions, is an urgent priority for the global eradica- tion initiative. The countries which now remain endemic for polio include countries affected by civil unrest or military conflict, or politically isolated countries (e.g., Democratic People's Republic of Korea, Somalia, Sudan, the Democratic Republic of Congo), which serve as important remaining reser- voirs from where wild poliovirus continues to spread into bordering or even distant polio-free countries. Expansion of the eradication initiative into these countries is critical to achieve global eradication. External support will continue to be required by those countries and regions where the inci- dence of polio has reached low levels, to ensure that final chains of poliovirus transmission are in- terrupted and to permit the eventual certification of eradication. Sufficient external support will en- sure continued implementation and improve- ments of the recommended strategies. The year- 2000 objective for achieving poliomyelitis eradica- tion remains a feasible target. Summary Substantial progress towards the global eradication of poliomyelitis by the year 2000 has been achieved since May 1988 when WHO Member States adopted this goal at the Forty-first World Health Assembly. Virtually all polio-endemic countries have begun to implement the WHO-recommended strategies to eradicate polio and it is expected that, by the end of 1997, all endemic countries in the world will have conducted full National Immunization Days (NID), providing supplemental oral polio vaccine (OPV) to nearly two-thirds of all children < 5 years. In contrast, although globally acute flaccid paralysis (AFP) surveillance was being conducted in 126 (86%) of 146 countries where polio is or recently was endemic, surveillance remains incomplete and un- timely. A global network of polio laboratories, capable of detecting wild poliovirus when and where it occurs, has been developed. Furthermore, in countries where polio virus circulation has been limited to focal areas, and Rapp. trimest. statist. sanit. mond., 50 (1997) surveillance is adequate, mopping-up campaigns are being conducted to eliminate the final chains of trans- mission. The process for certification of polio eradica- tion has been established in each WHO region as well as atthe global level. The impact of the eradication initiative is evident, with an 88% decrease in the number of reported cases globally since 1988. In order to achieve the goal of eradication, the rapid development of com- plete and timely AFP surveillance and the continuation of effective NIDs constitute an urgent priority. This is of particular relevance in the remaining polio-endemic countries, especially in those that are affected by war or politically isolated and are important remaining reser- voirs from where wild poliovirus continues to spread into bordering or even distant polio-free countries. External support will continue to be required by those countries and regions where the incidence of polio has reached low levels to ensure that final chains of poliovirus trans- mission are interrupted and to permit the eventual cer- tification of eradication. The year 2000 objective for achieving poliomyelitis eradication remains a feasible target. Resume Situation actuelle de /'eradication de la poliomyelite dans le monde Des progres importants en vue de !'eradication mondia- le de la poliomyelite d'ici l'an 2000 ant ete realises depuis mai 1988, date a laquelle les Etats Membres de l'OMS ant adopte ce but lors de la Quarante et Unieme Assemblee mondiale de la Sante. Pratiquement tousles pays d'endemie ant commence a mettre en reuvre les strategies recommandees par l'OMS afin d'eradiquer la poliomyelite et l'on espere que, d'ici la fin de 1997, tous les pays d'endemie auront organise des journees natio- nales de vaccination (JNV), administrant des doses supplementaires de vaccin antipoliomyelite buccal (VPO) a pres des deux tiers des enfants ages de mains de 5 ans. En revanche, meme si, au niveau mondial, une surveillance de la paralysie flasque aigue (PFA) est en vigueur dans 126 pays (86%) sur les 146 ou la polio- myelite sevit ou sevissait encore recemment a l'etat endemique, la surveillance demeure incomplete et n'est paseffectueeen tempsopportun. Un reseau mondial de laboratoires de la poliomyelite capable de deceler le poliovirus sauvage quand et la ou ii sevit a ete mis en place. Par ailleurs, dans les pays ou la circulation du. virus a ete limitee a des zones localisees, et ou la surveillance est suffisante, des campagnes de vaccina- tion de rattrapage sont organisees pour eliminer les dernieres chaines de transmission. Le processus de certification de !'eradication de la poliomyelite a ete etabli dans chacune des regions de l'OMS aussi bien qu'au niveau mondial. L'impact de !'initiative en faveur de !'eradication est evident, puisqu'une diminution de 88% du nombre de cas notifies dans le monde a deja ete observee depuis 1988. Pour atteindre le but de !'eradi- cation, la mise en place rapide d'une surveillance corn- Wld hlth statist. quart., 50 (1997) plete en temps opportun de la PFA et la poursuite des JNV constituent une priorite urgente. Cela est particulie- rement important dans les pays d'endemie restants, en particulier dans les pays touches par la guerre ou isoles politiquement et qui constituent des reservoirs impor- tants, d'ou le poliovirus sauvage continue de se propa- ger dans des pays indemnes de poliomyelite voisins ou plus eloignes. Une aide exterieure continuera d'etre necessaire dans les pays et les regions ou !'incidence de la poliomyelite est tombee a des niveaux peu eleves pour s'assurer que les dernieres chaines de transmis- sion du poliovirus sont interrompues et permettre la certification de !'eradication. L'objectif de !'eradication de la poliomyelite en l'an 2000 reste une cible realisable. References/References l. Hull, H.F. et al. 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