(1 table, 1 figure omitted)
In 1988, the World Health Assembly
resolved to eradicate poliomyelitis globally by 2000.1 A
plan of action for polio eradication in the Western Pacific Region
(WPR) by 1995 was adopted in 1990. The plan was based on routine and
supplemental vaccination activities with oral poliovirus vaccine (OPV)
and acute flaccid paralysis (AFP) surveillance in the eight countries
where polio was endemic (Cambodia, China, Laos, Malaysia, Mongolia,
Papua New Guinea, Philippines, and Vietnam).2 Regionwide,
the number of reported polio cases decreased from approximately 6000 in
1990 to zero in 1998. This report describes the extensive efforts to
eliminate the last chains of poliovirus transmission in the Mekong
River area.
AFP surveillance was introduced in Cambodia, Laos, and Vietnam in
1992, and has improved steadily (during 1994-1997, the proportion of
AFP cases with two adequate stool samples increased from 7% to 71% in
Cambodia, 0 to 70% in Laos, and 49% to 84% in Vietnam). From 1992 to
1997, the number of confirmed polio cases decreased from 557 to one in
Vietnam; from 146 to eight in Cambodia; and from seven to zero in Laos.
In addition, analysis of 1996 data suggested that poliovirus
transmission was limited to focal areas in Cambodia, Laos, and Vietnam.
During 1996, 21 confirmed cases of polio were reported in WPR (17 cases
from the Mekong River area of Cambodia, one from nearby southern Laos,
and three imported into China from Myanmar).3
National Immunization Days (NIDs)* were conducted from
1993 through 1998 in Vietnam and Laos, and from 1995 through 1998 in
Cambodia. A total of 12.5 million children were targeted in the three
countries during each round of NIDs, and the reported coverage was
generally high. During January-March 1997, nine polio cases were
reported from the Mekong River area. Analysis of data from supervisory
teams and AFP surveillance indicated that a substantial proportion of
undervaccinated children were residing on the extensive waterways of
the Mekong River and many had been missed previously by both routine
and supplemental vaccination activities. Therefore, to interrupt the
transmission of wild poliovirus in 1997, additional rounds of
supplemental vaccination focused on these unreached areas and
populations. Cambodia, Laos, and Vietnam conducted two synchronized
rounds of "mopping-up"† supplementary vaccination in high-risk
areas in May and June 1997; the second two rounds in Cambodia and
Vietnam occurred during February-April 1998.
A combination of strategies, including fixed and mobile vaccination
sites and mobile teams, were used to ensure that every child aged <5
years in the selected areas would receive two doses of OPV, regardless
of vaccination history. In many areas, hundreds of mobile teams, using
a ratio of one team for each 120 children, visited from house to house
and boat to boat to reach the target population.
Because an accurate target denominator was unknown, coverage data
were considered unreliable for monitoring the quality of mopping-up.
Therefore, the total number of children reached by mobile teams and the
proportion of children for whom no vaccination dose ("zero-dose"
children) was recorded previously served as an alternative indicator of
the quality of the mopping-up rounds. In Cambodia, the proportion of
"zero-dose" children in selected areas decreased from 22% during
the first round in May 1997 to 1% in 1998.
AFP surveillance data indicated that the last person reported with
polio in WPR had onset of illness in Cambodia on March 19, 1997. No
other cases of polio have been detected in WPR despite the reporting
and investigation of >9000 AFP cases in 1998 (data as of December 10,
1998); two stool samples had been taken from 85% of persons with cases
within 14 days of onset of paralysis. Vietnam reported 463 AFP cases
(nonpolio AFP rate of 1.5 per 100,000 population aged <15 years) in
1997 and 492 cases (nonpolio AFP rate of 1.7) in 1998 (data as of
December 10). In 1997, stool specimens were available from 83% of
persons with AFP, and in 1998, from 95%.
Cambodia reported 178 AFP cases in 1997 and 142 cases in 1998,
for nonpolio AFP rates of 3.2 and 2.8, respectively. Despite problems
with transport and communication, adequate stool sampling rates of 71%
in 1997 and 80% in 1998 were achieved in Cambodia. Laos reported 76
AFP cases in 1997, for a nonpolio AFP rate of 3.5. The number of AFP
cases reported in 1998 was 75, and the nonpolio AFP rate was 3.7.
Adequate stool collection rates for 1997 and 1998 were 75% and 77%,
respectively.
CDC Editorial Note:
Countries in WPR have conducted polio eradication efforts since 1991,
and WPR is now apparently polio-free. To complete eradication, Cambodia
and Vietnam conducted eight supplementary vaccination rounds: four
rounds of mopping-up and four rounds of NIDs in the high-risk areas
along the waterways of the Mekong River and its tributaries from
November 1996 through April 1998. These waterways support large
populations, many of whom are highly mobile and not regularly reached
by routine vaccination services. The supplemental vaccination efforts
appear to have been successful in
eliminating the last remaining reservoirs of wild
poliovirus in WPR.
CDC Editorial Note:
To reach a high proportion of the target groups for mopping-up
vaccination, substantial efforts were devoted to planning, monitoring
and supervision, and evaluation. The planning process used high-quality
AFP and laboratory surveillance data to identify target areas. The
timely availability of laboratory results from stool specimens enabled
the precise location of wild polioviruses within 60 days of onset of
paralysis for 85% of cases. The criteria for selecting high-risk
districts included those with wild poliovirus during the preceding 24
months, clusters of clinically confirmed polio cases, poor surveillance
performance, boat-dwelling populations, and borders with other
countries where polio is endemic. In timing mopping-up, it was
considered more important to choose the better access afforded by the
hot, dry summer months rather than the low transmission for
enteroviruses during the winter season.
CDC Editorial Note:
Each district and subdistrict prepared logistic plans showing
population, vaccine, staff and other requirements, and maps to locate
the position of vaccination posts and routes to be taken by mobile
teams. In certain areas, aerial photography was used over the waterways
to locate boat-dwelling populations.
CDC Editorial Note:
In Cambodia and Vietnam, 1 million children aged <5 years were
included in both the 1997 and 1998 mopping-up, and Laos, which
conducted mopping-up in 1997 only, targeted 50,000 children aged <5
years. In Cambodia, the mopping-up rounds were staggered over 12 days
to allow time for supervisory teams to visit all areas; 14 days were
used in Laos, and 3 days in Vietnam. Given the large amount of
cross-border traffic between Cambodia and Vietnam, special efforts were
made to coordinate the mopping-up by synchronizing the dates, and
deploying mobile teams and fixed posts at border crossing points.
CDC Editorial Note:
Despite initial concerns regarding a potential negative effect of polio
eradication on routine vaccination, routine coverage with three doses
of OPV among 1-year-old children increased substantially during
1993-1997 (Cambodia from 36% to 70%, Laos from 26% to 69%, and
Vietnam from 91% to 95%).
CDC Editorial Note:
The efforts needed to interrupt the final chains of poliovirus
transmission in the last few remaining areas were far more intense than
in the early stages when polio was widely endemic. Critical conditions
for the success of the mopping-up were 1) availability of high-quality
AFP and virological surveillance to identify high-risk areas; 2) timely
analysis of surveillance data to identify areas not reached by previous
supplementary vaccination rounds; 3) timely availability of laboratory
results to identify areas where wild poliovirus was circulating; 4)
detailed local planning including the use of maps at the
sub-district level; and 5) use of new vaccination approaches, including
mobile teams to reach all target children.
*Mass campaigns over a short period (days to weeks) in
which two doses of OPV are administered to all children in the target
group (usually aged 0-4 years) regardless of previous vaccination
history, with an interval of 4-6 weeks between doses.
† Focal mass campaign in high-risk areas over a short period (days to
weeks) in which two doses of OPV are administered during house-to-house
and boat-to-boat visits to all children in the target age group,
regardless of previous vaccination history, with an interval of 4-6
weeks between doses.
1 table, 2 figures omitted
Since the 1988 World Health Assembly resolution
to eradicate poliomyelitis by 2000, polio cases reported globally have
decreased by approximately 85%.1 Despite a strong
commitment to polio eradication, polio remains endemic in Pakistan. In
1997, Pakistan reported 1147 polio cases, representing widespread
poliovirus circulation nationally and constituting 22% of cases
reported worldwide. However, surveillance and laboratory data from 1998
indicate that previous widespread poliovirus circulation was
geographically localized for the first time. This report describes
polio eradication activities in Pakistan, including the impact of
routine and supplementary vaccination on polio incidence.
Routine Vaccination Coverage
Routine Vaccination Coverage
Reported routine vaccination coverage with three or more
doses of oral poliovirus vaccine (OPV3) among children aged ≤1 year
decreased from 83% in 1990 to 57% in 1995, and increased to 75%-81%
during 1996-1998. In Pakistan during January 1998, cluster
surveys conducted in 13 districts revealed a median routine OPV3
coverage of 58% (range: 10%-93%), compared with 71% coverage based
on administrative data.
Supplementary Vaccination Coverage
Supplementary Vaccination Coverage
National Immunization Days* (NIDs). Annual NIDs, which delivered two doses of OPV to all children
aged <5 years, began in Pakistan in 1994. Since then, >20 million
children have been vaccinated each year, with coverage reported at
>95% during each of 10 NID rounds. NIDs in 1994 and 1995 were
conducted during high poliovirus transmission season to coordinate with
NIDs held in neighboring countries; subsequent NIDs have been conducted
during Pakistan's low polio season during December-February. In three
districts following the December 1997 NID, cluster surveys revealed a
median coverage of 87%. NIDs also were conducted in December 1998
(round 1) and January 1999 (round 2); during the first round, 26
million children were vaccinated, representing the highest number of
children vaccinated in Pakistan.
Supplementary Vaccination Coverage
Cross-border vaccination activities. Pakistan implemented cross-border supplemental vaccination
activities in all districts bordering Iran and Afghanistan. During NIDs
in Iran in March and April 1998, an average of 177,000 Pakistani
children (85% of the target) were vaccinated in each of two rounds
through house-to-house vaccinations in five border districts in
Balochistan. During NIDs in Afghanistan in
May and June 1998, 2,110,000 (round 1) and
1,660,000 (round 2) Pakistani children were vaccinated in 22 districts
in Balochistan and Northwest Frontier Province (NWFP), reaching
>100% of target children in each round.
Supplementary Vaccination Coverage
Outbreak response. Outbreak response consisted of
administering two doses of OPV to children aged <5 years through
house-to-house vaccinations throughout the outbreak district. In 1997,
approximately 200,000 children were vaccinated during each of two
rounds in the districts of Bannu, Lakkimarwat, and Quetta.
Acute Flaccid Paralysis Surveillance
Acute Flaccid Paralysis Surveillance
Acute flaccid paralysis (AFP) surveillance was introduced in
Pakistan in 1995, and by 1998, staff in all provinces were trained in
AFP surveillance and were sending monthly case reports to the Expanded
Program on Immunization (EPI) office. AFP surveillance was strengthened
through surveillance assessments in many districts and introduction of
computerized case line listings at the provincial and national levels.
The poliovirus laboratory at the National Institutes of Health in
Islamabad serves as both the National Poliomyelitis Laboratory and the
WHO Regional Reference Laboratory for Poliomyelitis; it performs
primary poliovirus isolation from stool specimens and intratypic
differentiation of poliovirus.
Acute Flaccid Paralysis Surveillance
To monitor AFP surveillance performance, a reported nonpolio AFP
rate of ≥1 per 100,000 population aged <15 years is used to indicate
a sensitive AFP surveillance system. In 1997, the nonpolio AFP rate was
0.7 nationally and was <1 in all provinces and territories. During
January-November 1998, the nonpolio AFP rate was 0.6, with no increase
in case findings compared to 1997. The proportions of cases with
adequate stools (61%) and 60-day follow-up for residual paralysis
(75%) increased in 1998; however, the goals of reaching 80% for both
parameters have not been achieved.
Impact of Eradication Activities
Impact of Eradication Activities
Although NIDs have substantially decreased polio cases since 1993
(when 1803 cases were reported), the number of reported cases still
remains high. In 1997, Pakistan reported 1147 polio cases; these cases
represented widespread poliovirus circulation because poliovirus type 1
was identified in 86 (72%) of the 120 districts and poliovirus type 3
in 24 (20%) districts in 18 (75%) of Pakistan's 24 divisions.
Poliovirus type 2 was isolated from two cases from NWFP in 1997. In
addition to widespread endemic polio in 1997, four outbreaks of >30
cases each occurred in four districts in NWFP and Balochistan,
Pakistan.
Impact of Eradication Activities
Through November 1998, 277 polio cases reported in 1998
have been confirmed, a 74% decrease from the same period of 1997.
These cases occurred predominantly in children aged <3 years (83%)
and in children who received less than three doses of routine or
supplemental OPV (73%). In addition to substantial reduction in polio
incidence, previous widespread transmission has been limited following
the 1997-1998 NIDs to three main areas—Karachi, southern Sindh
(Hyderabad division), and central NWFP (Peshawar, Kohat, and Malakand
divisions). Cases confirmed by wild poliovirus type 1 isolation have
decreased by 75% from 1997 and were identified in 44 districts. Wild
poliovirus type 3, however, has been found in 25 districts in 1998,
with no decrease from 1997. No wild poliovirus type 2 has been isolated
in 1998, and no outbreaks of >20 cases had occurred as of November
1998.
CDC Editorial Note:
Laboratory and surveillance data suggest that after 4 years
of eradication efforts in Pakistan, previous widespread poliovirus
transmission has been reduced greatly, with sustained transmission
limited to focal geographic areas. Polio cases have been reduced by
74% from 1997 to 1998, with an 88% decrease in the most populous
province (Punjab). Wild poliovirus type 2 has not been isolated as of
November 1998, and the number of poliovirus genotypes circulating in
1998 has been reduced.2 The reduced polio incidence in 1998
may be attributed to improved NIDs, cross-border vaccination
activities, outbreak response vaccination, and immunity caused by
previous widespread virus circulation.
CDC Editorial Note:
Pakistan conducted five sets of NIDs before reaching the level of
poliovirus control observed in 1998. Reasons for delayed impact of
polio eradication activities may include conducting the first two sets
of NIDs during the high poliovirus circulation season, nonuniform
coverage for both NID and routine vaccination, and low routine OPV3
coverage. The Pakistan experience indicates that among densely
populated countries with a warm climate and poor sanitation such as
Pakistan, NIDs may have a rapid impact on polio incidence only in the
presence of high routine vaccination.3
CDC Editorial Note:
Surveillance indicators suggest that case finding and
investigation should be strengthened. Efforts to improve AFP
surveillance will include hiring surveillance coordinators in each
large province, monthly monitoring visits to each district, and
inter-divisional meetings to review surveillance and provide additional
training.
CDC Editorial Note:
To eradicate polio from Pakistan, successful NIDs and other
routine and supplementary vaccination activities should be continued
and strengthened. Efforts to improve routine vaccination will include
assuring a steady vaccine supply, expanding vaccine delivery to all
primary health-care sites, and renewed training and social mobilization
to ensure consumer demand for vaccination. Other supplementary
vaccination activities, such as a third NID round or subnational NIDs
in high-risk areas, will be necessary to assure rapid progress to meet
the 2000 goal. Pakistan will expand supplemental vaccination activities
in high-risk areas in spring 1999 to include all high-risk districts in
Sindh, Balochistan, and NWFP. Strong support from the Pakistan
government and international partners will be necessary to continue the
substantial progress observed in 1998.†
*Mass campaigns held over a short period of time (days
to weeks) in which two doses of oral poliovirus vaccine are
administered to all children in the target group, regardless of prior
vaccination history, with an interval of 4-6 weeks between doses.
† Polio eradication in Pakistan is supported by the governments of
Pakistan, Japan, and the United Kingdom; WHO; United Nations
Children's Fund (UNICEF), CDC, and Rotary International.