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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 In 2000, before the initiation of SIAs, measles vaccination coverage increased to 69% (Cambodian Ministry of Health, unpublished data, 2001).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.
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.
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.
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