Progress Toward Poliomyelitis Eradication -- Western Pacific Region, January 1, 1996-September 27, 1997

In 1988, the World Health Assembly adopted the goal of global poliomyelitis eradication by 2000 (1), which was endorsed in each of the six regions of the World Health Organization (WHO) (2). In the Western Pacific Region (WPR), where the last known case of polio associated with isolation of wild poliovirus occurred in March 1997, the reported number of cases decreased from 5963 in 1990 to 197 in 1996. This report documents progress toward polio eradication in WPR from January 1, 1996, through September 27, 1997, in countries where polio is endemic (Cambodia, China, Laos, Papua New Guinea, Philippines, and Vietnam) or recently was endemic (Malaysia and Mongolia) (3-6) and describes the routine and supplemental vaccination activities necessary to interrupt wild poliovirus transmission in the region. Routine Vaccination Coverage

In all 36 WPR countries, oral poliovirus vaccine (OPV) is used for routine vaccin-ation of infants. In 1996, regional coverage with three doses of OPV (OPV3) by age 1 year was 95% (country-specific range: 57%-96%), an increase compared with the year-specific coverage during 1993, 1994, and 1995 (92%, 92%, and 93%, respectively). During 1993-1996, routine OPV3 coverage increased substantially in Laos (from 26% to 68%), Cambodia (36% to 76%), and Papua New Guinea (46% to 57%). National or Sub-National Immunization Days

Supplementary vaccination activities to interrupt widespread poliovirus circulation began in WPR during 1990 with Subnational Immunization Days (SNIDs) * in People's Republic of China. Except for Malaysia and Papua New Guinea, National Immunization Days (NIDs) have been conducted for at least 3 years in all countries where polio is endemic or recently was endemic, including Cambodia, China, Laos, Mongolia, Philippines, and Vietnam; Papua New Guinea is conducting its first full NIDs in 1997. Each year during NIDs, an estimated 105 million children (80%-95% of the target population) in WPR received two doses of OPV. High-Risk Response Immunizations

The goal of high-risk response immunizations (HRRIs) ** (similar to mopping-up activities in other regions) is to eliminate remaining focal reservoirs of wild poliovirus. Following the importation of four polio cases associated with wild poliovirus from Myanmar into Yunnan Province (China) during November 1995-April 1996, two rounds of HRRIs were conducted in the affected border area of Yunnan during March-April 1996.

Based on surveillance data, the last focus of wild poliovirus transmission in WPR is in the Mekong River and Tonle Sap Lake areas of Cambodia and Vietnam. Wild poliovirus was identified in those areas until early 1997 despite reported high supplemental vaccination coverage in both countries. To interrupt wild poliovirus transmission in these areas, HRRIs were conducted in Cambodia, Laos, and Vietnam during May-July 1997 (Figure_1). Surveillance

In WPR, 5291 cases of acute flaccid paralysis (AFP) were reported with onset in 1996 (nonpolio AFP rate of 1.2 per 100,000 (Table_1). Two adequate stool specimens were obtained from 79% of AFP cases, and at least one specimen was collected from 94%. Of the 5291 cases, 197 were identified as polio based on clinical (176 cases) and virologic (21) classification criteria ***. Of the 21 wild poliovirus-associated cases, 17 were in children in Cambodia and Vietnam (near the lower Mekong River and its delta), one was in a child in southern Laos, and three were in children from Myanmar who were taken to hospitals in Yunnan Province.

As of September 27, 1997, a total of 3796 cases of AFP were reported with onset in 1997 in WPR (projected annual nonpolio AFP rate of 1.1 per 100,000); two adequate stool specimens were collected for 82% of these. Nine of the 3796 AFP cases have been confirmed as polio by isolation of wild poliovirus; eight of these nine confirmed cases (including the last wild poliovirus-associated case) were in children in the same areas of Cambodia as children with confirmed cases in 1996, and the ninth was in a child from Vietnam (Figure_1). During 1996-1997, all virus-confirmed polio cases (except for two of the imported cases in China, which were type 3) were associated with wild poliovirus type 1.

All countries in WPR where polio was recently endemic (except for Papua New Guinea) have reached or exceeded the WHO-established minimum rate of AFP, which indicates a sensitive surveillance system (i.e., greater than or equal to 1 nonpolio AFP case per 100,000 children aged less than 15 years). Except for Papua New Guinea, the percentage of AFP cases for which specimens were adequate (i.e., two specimens collected within 14 days of onset of paralysis) is projected to be greater than or equal to 60% by the end of 1997 for all countries where polio recently was endemic; this indicator is greater than or equal to 80% in China, Laos, and Vietnam. Laboratory Network

The regional polio laboratory network consists of 13 laboratories (10 national laboratories, two regional reference laboratories, and one specialized reference laboratory) (7). In addition, there are 30 provincial laboratories in China. A passing score (greater than or equal to 80%) was achieved by six of the 10 network laboratories that underwent proficiency testing during 1997 and by 29 of the 30 provincial laboratories in China during 1996. From 1995 to 1997, the average interval from onset of paralysis to reporting of results of intratypic differentiation of isolates (vaccine-related versus wild poliovirus) improved throughout the region (e.g., in China from 127 days to 81 days and in Cambodia from 211 days to 46 days). Genomic sequencing data are available from all recent isolates of wild poliovirus. Certification of Polio Eradication

The Regional Commission for the Certification of Poliomyelitis Eradication in WPR was convened April 15-16, 1996. To be certified, a WPR country must demonstrate evidence consistent with the absence of wild poliovirus for 3 years; all countries where polio is endemic must demonstrate that high-quality AFP surveillance has been maintained. National certification committees and a special subregional committee for the Pacific island countries will compile the documentation needed for certification for each country. Those countries that have been polio-free for an extended period (i.e., greater than 5 years) also must demonstrate a capacity to respond to detected importation of wild poliovirus.

Reported by: Expanded Program on Immunization and Poliomyelitis Eradication Unit, Regional Office for the Western Pacific, World Health Organization, Manila, Philippines. 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; Polio Eradication Activity, National Immunization Program, CDC.

Editorial Note

Editorial Note: WPR is likely to be the second WHO region (following the Western Hemisphere {WHO Region of the Americas} {8}) to eliminate the last remaining chains of wild poliovirus transmission. This progress was accomplished by conducting high-quality NIDs, SNIDs, and HRRIs; sustaining and further improving already high levels of routine vaccination in China, Malaysia, Mongolia, Philippines, and Vietnam; dramatically improving low levels of routine vaccination in Cambodia, Laos, and Papua New Guinea during 1993-1996; and establishing sensitive systems for surveillance. The quality of surveillance has improved in all countries where polio is endemic and is expected to reach the levels necessary for certification.

Enhanced surveillance and timely availability of laboratory results have been critical to identify and target intense vaccination activities to the last areas with known or suspected circulation of wild poliovirus. Detailed and timely information about AFP cases is available to program managers, and wherever wild poliovirus transmission is suspected or confirmed, rapid action has been taken. The mapping of key surveillance data (i.e., distribution of "polio-compatible" AFP cases) and detailed vaccination coverage information were essential in identifying high-risk areas for HRRIs in Cambodia, Laos, and Vietnam in 1997.

The governments of WPR countries have provided the largest share of the resources needed for polio eradication in the region. In addition, essential technical and financial support has been provided by WHO; United Nations Children's Fund (UNICEF); and other partner agencies, especially Rotary International, the government of Japan through JICA, the government of Australia through AusAID, and the U.S. government through CDC.

Seven months have elapsed since wild poliovirus was last detected in WPR. For the region to be certified as polio-free by 2000, there can be no new cases of indigenous wild poliovirus in 1998 and beyond. This goal probably will be met because 1) polio eradication continues to be given high priority in the countries concerned; 2) by the end of 1997, six rounds of high-quality supplementary vaccination will have been conducted in the areas with known transmission during the previous 14 months, with additional rounds planned for early 1998; and 3) all countries are now approaching or exceeding the level of AFP surveillance needed to ensure confidence in their reports of polio-free status and required for certification. Sustaining the momentum needed to achieve and maintain regional and global certification requires the continuation of high-quality surveillance, external funding, national priority of polio eradication in participating countries, and rapid progress in the global eradication initiative.

References

1. World Health Assembly. Global eradication of poliomyelitis by the year 2000. Geneva, Switzerland: World Health Organization, 1988. (Resolution no. WHA41.28).

2. Regional Committee for the Western Pacific, World Health Organization. Eradication of poliomyelitis by 1995. Manila, Philippines: World Health Organization, Regional Committee for the Western Pacific, 1988. (Resolution no. WPR/RC39.R15).

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

4. CDC. Progress toward poliomyelitis eradication -- People's Republic of China, 1990-1994. MMWR 1994;43:857-9.

5. CDC. Progress toward poliomyelitis eradication -- Socialist Republic of Vietnam, 1991-1993. MMWR 1994;43:387-91.

6. CDC. National immunization days and status of poliomyelitis eradication -- Philippines, 1993. MMWR 1994;43:6-9,13.

7. CDC. Status of the global laboratory network for poliomyelitis eradication, 1994-1996. MMWR 1997;46:692-4.

8. CDC. Certification of poliomyelitis eradication -- the Americas, 1994. MMWR 1994;43:720-22.

* Mass campaigns over a short period (days to weeks) during which two doses of OPV are administered to all children in the target age group (usually 0-4 years) regardless of previous vaccination history, with an interval of 4-6 weeks between doses.

** Planned mass vaccination campaigns over a short period (days to weeks) in response to ongoing poliovirus transmission in which two doses of oral poliovirus vaccine are administered to all children in the target group (usually 0-4 years) regardless of previous vaccination history, with an interval of 4-6 weeks between doses, and providing these doses by going house-to-house and boat-to-boat to reach those children that have not been reached previously by routine or supplemental vaccination activities.

*** In 1996 and 1997, virologic classification criteria were used by China and Vietnam; all other countries used clinical criteria.

TABLE 1. Number of reported cases of acute flaccid paralysis (AFP) and confirmed poliomyelitis and key surveillance
indicators among countries with AFP surveillance, by country and year -- Western Pacific Region (WPR), World Health
Organization, January 1996-September 1997
===================================================================================================================================

                                          1996                                                    1997
                  -------------------------------------------------------   -----------------------------------------------------
                                                        No. confirmed                                           No. confirmed
                                                         polio cases                                             polio cases
                   No. AFP   AFP with                --------------------   No. AFP   AFP with               --------------------
                   cases    adequate     Nonpolio              Wild virus    cases    adequate   Nonpolio              Wild virus
Country           reported  specimens *  AFP rate +  Clinical  associated   reported  specimens  AFP rate &  Clinical  associated
---------------------------------------------------------------------------------------------------------------------------------
Cambodia             134       50%         0.9           84        15          112       73%       1.7           40         8
China               4372       83%         1.4            3         3         3033       86%       1.3            0         0
Laos                  41       41%         0.9           21         1           55       80%       3.3            2         0
Malaysia              32       34%         0.3            3         0           37       32%       0.5            0         0
Mongolia              19       62%         1.5            0         0           10       70%       1.0            0         0
Papua New Guinea      14        9%         0.5            4         0           15       13%       0.8            3         0
Philippines          175       41%         0.3           80         0          253       49%       1.0           54         0
Vietnam              495       81%         1.7            2         2          276       84%       1.3            1         1

Pacific island
  countries @          6        0          0.7            0         0            4        0        0.6            0         0

Others **              3       33%         0              0         0            1      100%       0              0         0

Total               5291       79%         1.2          197        21         3796       82%       1.1          100         9
---------------------------------------------------------------------------------------------------------------------------------
 * Two stool specimens collected 24-48 hours apart within 14 days of paralysis onset.
 + Per 100,000 children aged <15 years.
 & Annualized nonpolio AFP rate.
 @ These countries have been grouped together for reporting purposes.
** Countries of WPR where polio is not endemic or has not been recently endemic.
===================================================================================================================================

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