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Accelerated Measles Control --- Cambodia, 1999--2002
Cambodia is recovering from approximately 30 years of civil war that
resulted in the breakdown of the country's public health infrastructure (1).
In 1999, the Ministry of Health initiated a measles-control program with the
goal of reducing the annual incidence of measles to <10,000 cases in 2005 by
strengthening measles surveillance, improving routine vaccination coverage,
implementing supplementary measles immunization activities (SIAs), and
providing vitamin A during outbreak investigations and SIAs. This report
summarizes measles-vaccination activities and their impact in reducing
reported measles cases from 13,827 in 1999 to 1,234 in 2002 and suggests
options for future measles-control efforts in postconflict situations.
Routine and Supplementary Vaccination
Routine measles vaccination began at Cambodian health centers in 1986,
with outreach activities added in 1990 and SIAs in 2000. The most basic
organizational component of the health-care delivery system is the health
center, each serving approximately 10,000 persons. Many villages lack easy
access to these facilities, and only 30% of children had access to
vaccination services during the early 1990s. Since 1990, outreach teams from
health centers have visited villages every 4--8 weeks to deliver vaccination
and other preventive health services. These outreach services helped
increase coverage for measles vaccination in the country from 34% in 1990 to
75% in 1995, although coverage declined to 63% during 1998--1999, after a
resurgence of civil unrest in 1997. In 2000, before the initiation of SIAs,
measles vaccination coverage increased to 69% (Cambodian Ministry of Health,
unpublished data, 2001).
The Cambodian National Immunization Program (NIP), in collaboration with
partner agencies, initiated measles SIAs in December 2000 to vaccinate
children who were missed by routine services. The initial plan was to
vaccinate all children aged 9 months--5 years, regardless of previous
vaccination history, in two phases. After Phase I, the subsequent phase was
expanded in 2001 to include children aged 9 months--14 years after a review
of measles surveillance data indicated that approximately 50% of measles
cases occurred in children aged >5 years. To avoid overextending the public
health system of the country and compromising the quality of the campaign,
the second phase was then divided into two (phases II and III).
Phase I, conducted during December 2000--May 2001, targeted 191,527
children aged <5 years living in remote border areas who were administered
multiple vaccines (measles, oral polio vaccine [OPV],
diphtheria-tetanus-pertussis vaccine), vitamin A, and mebendazole for
helminth control; an 89% coverage rate with measles vaccine was attained.
Phase II, conducted during October 2001--April 2002, targeted 2,489,761
children aged 9 months--14 years living in eight provinces in densely
populated central areas. These children were administered measles vaccine,
OPV (in selected areas), vitamin A, and mebendazole; a 97% coverage rate
with measles vaccine was attained. Phase III, which began in October 2002
and will continue through April 2003, will target approximately 2,300,000
children aged 9 months--14 years living in the remaining seven provinces in
central areas with measles vaccine, OPV (in selected areas), vitamin A, and
mebendazole.
SIAs are conducted in a "rolling" manner, which cover one province at a
time by teams comprising local, district, and provincial Expanded Program on
Immunization (EPI) staff, with supervision by staff from the national
program. Each district is covered in approximately 2 weeks. SIAs are
preceded by social mobilization activities in which local volunteers and
community leaders publicize the upcoming activities. Temporary vaccination
posts operate in the mornings and are followed by house-to-house vaccination
in the afternoons. House-to-house vaccination is particularly necessary in
densely populated urban areas, where social mobilization might not be as
effective as in villages.
Surveillance and Outbreak Response
Data on measles incidence before 1999 are limited. The World Health
Organization (WHO) assisted NIP in conducting 30 outbreak investigations
during 1999, recording 1,423 cases, including 14 deaths (case fatality
ratio: 1%). In addition, 80 (5.6%) persons showed signs of vitamin A
deficiency, and six (0.4%) had encephalitis. In 1999, surveillance was
strengthened through the addition of an active search for measles cases
during routine outreach visits by EPI staff. Outreach visits detected an
estimated 95% of reported measles cases (K. Feldon, M.P.H., WHO Cambodia,
personal communication, 2002).
On receiving a report of a measles outbreak from an outreach team, an
investigation is conducted approximately 1--4 weeks later by provincial,
district, and health center staff. In each village, treatment with vitamin A
at the WHO-recommended dosage (2) is provided to all persons with
measles to prevent complications and as a prophylaxis to all children aged
<12 years. Monetary incentives are provided to EPI staff for reporting an
outbreak and to national, provincial, district, and health center staff for
conducting the investigation.
Serologic confirmation of outbreaks began in three of the 24 provinces in
early 2000 and is now standard in eight provinces. Samples are collected
from the first five cases of each outbreak. Testing for measles IgM
antibodies is conducted by the National Reference Laboratory in Phnom Penh.
Measles Incidence
The peak of measles transmission in Cambodia occurs during the hot dry
season (November--April). In 1999, when the surveillance system covered six
of 24 provinces, NIP received reports of 13,827 measles cases. In 2000,
following expansion of measles surveillance nationwide, Cambodia reported
11,940 cases with case reports from 21 provinces. In 2001, the number of
reported cases decreased to 3,696 distributed among 19 provinces. Measles
incidence continued to decline in 2002, with 1,234 cases reported from 11
provinces as of October 18 (Figure).
During January 2000--October 2002, a total of 94%--99% of reported
measles cases occurred among persons aged <15 years. The proportion of cases
among children aged <5 years decreased from 47% in 2000 to 36% in 2001 and
35% in 2002 (Table). Among patients aged <10 years, the
proportion with a history of previous measles vaccination has remained
steady, ranging from 23% in 2000 to 27% in 2002.
Reported by: SC Soeung, MD, S Sarath, MD, C Morn, MD, Y Nareth,
MD, National Immunization Program, Ministry of Health; K Feldon, MPH, World
Health Organization, Cambodia. J McFarland, MD, World Health Organization
Regional Office for the Western Pacific, Manila, Philippines. RT Perry, MD,
P Strebel, MBChB, Global Immunization Div, National Immunization Program; R
Nandy, MBBS, EIS Officer, CDC.
Editorial Note:
The marked decrease in the annual number of reported measles cases in
Cambodia during 2000--2002 is attributable in part to increases in routine
vaccination coverage and to SIAs conducted during the previous 3 years. In
addition, the decrease might reflect the natural decline in incidence
following an epidemic. Consistent with the low measles vaccination coverage
in Cambodia, the majority of cases continue to occur among children aged <10
years and among unvaccinated persons.
Providing routine vaccinations through outreach visits to villages has
improved vaccination coverage in a country whose public health
infrastructure was destroyed by civil unrest and is being rebuilt. Although
vaccination activities began in 1986 with the formation of EPI, insecurity
in the countryside restricted the program to the capital and the surrounding
provinces. Large areas of the country remained inaccessible until 1996, and
only in 1998, when hostilities ceased, was travel possible throughout the
country.
Outreach visits also are a major component of the enhanced measles
surveillance system that was established in 1999 and helped overcome the
lack of information available in health-care facilities. The majority of
Cambodian children with measles are not brought to health-care facilities
because of a traditional belief that children should be kept at home during
the period of rash; as a result, health-care facility records are not useful
for measles surveillance. In addition, health-care workers do not inquire
routinely about a history of measles when evaluating a child with possible
measles complications (e.g., otitis media, pneumonia, diarrhea,
encephalitis, or corneal ulceration or scarring) (S. Sarath, M.D., NIP,
Cambodia, personal communication, 2002).
In addition, the strategy of implementing "rolling" SIAs effectively
reaches children who missed routine vaccination in infancy. SIAs have been
conducted in phases because of the limited health staff trained in
administering injections and inadequate cold chain facilities in Cambodia.
With this approach, a district is covered thoroughly, ensuring a
high-quality campaign and a high rate of vaccination coverage.
The findings in this report are subject to at least four limitations.
First, because the quality of surveillance and vaccine-coverage data has
improved substantially since 1999, comparisons with pre-1999 data are
difficult. Second, current surveillance systems might underreport the number
of cases in younger children and in persons from remote areas. Third, as
measles incidence (and the positive predictive value of clinical diagnosis)
decreases, the lack of capacity for laboratory confirmation might lead to
overreporting of true measles cases. Finally, estimating vaccination
coverage with the administrative method depends on accurate population
estimates and might overestimate the true coverage.
For measles control to be achieved, Cambodia will need to 1) increase
routine vaccination coverage further by using a combination of fixed
vaccination sites and outreach services, 2) continue periodic SIAs to reach
children missed by routine services, and 3) further strengthen measles
surveillance by enhancing data management and laboratory capacity. As the
number of measles cases decreases, laboratory confirmation of all reported
outbreaks will be necessary, requiring extension of laboratory confirmation
to all provinces. Lessons learned in Cambodia might be useful in planning
measles-control strategies in other postconflict settings, especially in
areas with few trained health staff and limited transportation and cold
chain facilities.
References
- Gollogly L. The dilemmas of aid: Cambodia 1992--2002. Lancet
2002;360:793--8.
- Expanded Programme on Immunization. Joint WHO/UNICEF statement on
vitamin A for measles. Wkly Epidemiol Rec 1987;62:133--4.
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