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Progress in Global Measles Control and Mortality Reduction, 2000--2006
The World Health Organization (WHO) and United Nations Children's Fund (UNICEF) comprehensive strategy for measles mortality reduction is focused on 47 priority countries.* Components include 1) achieving and maintaining high coverage (>90%) with the first dose of measles vaccine by age 12 months in every district of each priority country through routine immunization services; 2) ensuring that all children receive a second opportunity for measles vaccination; 3) maintaining effective case-based surveillance and monitoring of vaccination coverage; and 4) providing appropriate clinical management, including vitamin A supplementation (1). In 2005, the World Health Assembly set a goal for global measles control as part of the Global Immunization Vision and Strategy (GIVS) (2): a 90% reduction in measles mortality by 2010, compared with 2000 levels. In January 2007, WHO/UNICEF reported that implementation of measles mortality reduction strategies had reduced measles mortality by 60%, from an estimated 873,000 deaths in 1999 to 345,000 deaths in 2005 (3). This reduction exceeded the goal of 50% measles mortality reduction by 2005 (compared with 1999 levels) that had been set in 2002 (1,4). This report updates previous reports (5,6) by detailing 1) measles mortality reduction activities implemented during 2006 and 2) the impact of activities since 2000 on the global burden of measles and progress toward the GIVS mortality reduction goal for 2010.
WHO/UNICEF produces estimates of routine coverage with a single dose of measles vaccine on the basis of data from administrative records and surveys (7). Measles vaccination coverage levels achieved during supplementary immunization activities (SIAs) are estimated from the reported number of doses administered divided by the target population.
According to WHO/UNICEF estimates, global routine first-dose measles vaccination coverage reached 80% for the first time in 2006, increasing from 72% in 2000. Coverage varied substantially by WHO region (Table 1). From 2000 to 2006, the greatest improvements in routine coverage were observed in the WHO Africa Region (from 56% to 73%), the Eastern Mediterranean Region (73% to 83%), and the Western Pacific Region (86% to 93%). Despite this progress, in 2006, an estimated 26.2 million (20%) infants worldwide missed receiving their first dose of measles vaccine through routine immunization services by age 12 months (or by the time of vaccination if first dose was scheduled after 12 months). Of these, 12.8 million (49%) resided in the WHO South-East Asia Region, 7.5 million (29%) in the Africa Region, 2.3 million (9%) in the Eastern Mediterranean Region, and 1.8 million (7%) in the Western Pacific Region.
During 2000--2006, approximately 478 million children aged 9 months--14 years received measles vaccine through SIAs in 46 of the 47 priority countries. In 2006, a total of 25 (53%) of these 47 countries conducted SIAs, reaching approximately 136 million children (Table 2). Of the total SIA doses administered in 2006, 67% were administered in catch-up campaigns, and 33% were administered in follow-up campaigns. Of the 25 countries conducting SIAs in 2006, a total of 20 (80%) countries integrated at least one other child-survival intervention (e.g., administration of oral polio vaccine or distribution of insecticide-treated bednets) with measles vaccination (Table 2).
All WHO member countries are requested to report their annual measles case counts to WHO/UNICEF by means of a common form. Annual reporting of measles surveillance data increased from 169 (88%) member countries in 2000 to 180 (93%) in 2006. Effective surveillance for measles includes establishing case-based surveillance§ with laboratory testing of all suspected cases (8). In 2006, of 193 WHO member countries, 146 (76%) had implemented case-based surveillance, compared with 120 (62%) countries in 2004.
Countries report clinically, epidemiologically, or laboratory-confirmed measles cases. A 56% decrease was observed in the number of reported measles cases worldwide in 2006 (373,421), compared with 2000 (852,937). However, the number of reported cases in the European Region increased from 37,421 in 2000 to 53,344 in 2006, primarily because of large measles outbreaks in Ukraine and Romania. In addition, the number of reported cases in the South-East Asia Region increased from 78,574 in 2000 to 94,562 in 2006, primarily because of improved measles surveillance in India and Indonesia.¶
In settings with high measles vaccination coverage (i.e., where the majority of clinically suspected measles cases are likely to be attributed to nonmeasles causes of rash illness), laboratory confirmation is essential. In 1998, the WHO measles and rubella laboratory network (MRLN) consisted of fewer than 40 measles laboratories. By the end of 2006, this network had expanded to 678 national and subnational laboratories serving 164 countries. These laboratories perform enzyme-linked immunosorbent assays for measles immunoglobulin M (IgM) antibody on serum samples collected from persons with suspected measles during their first contact with a health facility. Testing of specimens for rubella IgM antibody also is performed in many countries on specimens testing negative for measles IgM antibody. Approximately 180,000 serum samples were tested worldwide in 2006, an increase from approximately 119,000 tested in 2005. Approximately 80% of laboratories met the timeliness performance target of reporting at least 80% of results within 7 days of receipt of the sample. Annual MRLN proficiency testing has been conducted since 2001. Of the 163 national laboratories that participated in the 2006 assessment, 160 (97.5%) met the proficiency requirement. A similar proficiency testing program has been established for subnational laboratories.
Mortality Estimates for 2006
Despite the global progress in measles surveillance and reporting, complete and reliable data on the number of measles deaths is lacking in many countries, particularly those with the highest disease burden. To estimate measles mortality, WHO updated a natural history model using 1) the most recent population data through 2006, 2) WHO/UNICEF routine vaccination coverage estimates and reported vaccination coverage from SIAs, and 3) country-specific measles incidence as reported to WHO for selected countries based on assessed quality of surveillance (3).
From 2000 to 2006, estimated measles deaths worldwide declined 68%, from 757,000 deaths (uncertainty bounds**: 551,000--990,000 deaths) in 2000 to 242,000 deaths (uncertainty bounds: 173,000--325,000 deaths) in 2006 (Table 1 and Figure). The largest percentage reduction in estimated measles mortality during this period was in the Africa Region (91%), accounting for 70% of the global reduction in measles mortality.
Reported by: A Dabbagh, PhD, M Gacic-Dobo, L Wolfson, PhD, D Featherstone, PhD, P Strebel, MBChB, JM Okwo-Bele, MD, Dept of Immunization, Vaccines, and Biologicals, World Health Organization, Geneva, Switzerland. E Hoekstra, MD, P Salama, MD, United Nations Children's Fund, New York, New York. S Wassilak, MD, A Uzicanin, MD, Global Immunization Div, National Center for Immunization and Respiratory Diseases, CDC.
In 2006, WHO/UNICEF estimates of global coverage with the first dose of measles vaccine reached the highest level ever reported, in large part because of increased routine measles vaccination coverage in countries of the Africa, Eastern Mediterranean, and Western Pacific regions. Increased routine measles vaccination coverage, combined with the estimated 478 million children vaccinated through SIAs in the 47 priority countries during 2000--2006 (327 million [68%] of whom resided in the Africa Region), has resulted in a 68% decrease in the estimated number of global measles deaths. The largest decrease in estimated measles deaths was observed in the Africa Region, which had already met the 2010 GIVS goal of 90% reduction in global measles mortality. The reduction in the South-East Asia region was substantially smaller (26%) because certain countries with large populations (e.g., India and Pakistan) had not yet begun large-scale measles SIAs and because little improvement in routine vaccination coverage had occurred. Pakistan initiated phased SIAs in 2007.
A key factor contributing to progress in reducing measles mortality in Africa has been support from the Measles Initiative, which was launched in 2001. With additional resources from the Global Alliance for Vaccines and Immunization§§ and the International Finance Facility for Immunization,¶¶ the Measles Initiative is expanding its support to countries with high measles burdens in other WHO regions, especially South-East Asia.
Measles vaccination campaigns are an opportunity to provide other interventions aimed at improving child survival, such as distribution of vitamin A supplements, delivery of insecticide-treated bednets to prevent malaria, and delivery of deworming medication. The majority of measles SIAs conducted in priority countries in 2006 were integrated with other child-survival interventions. Experience with combining essential health interventions with measles vaccination campaigns increases high-level political support, allows for resources to be pooled, and increases community participation (9). However, these interventions should be integrated in such a way as not to cause delays or reduce the quality of the SIAs (9).
Substantial improvements in measles surveillance, including improvements in reporting and timeliness of laboratory testing of specimens, have occurred since 2000. Nonetheless, reported measles case data should be interpreted with caution because of incomplete reporting of data to WHO, incomplete case detection and reporting in many countries, and the lack of case-based surveillance systems in nearly one fourth of countries.
Ongoing assessment is critical for guiding future measures for global measles mortality reduction. Because surveillance data do not allow direct measurement of global measles mortality, models must continue to be used for this purpose. Global measles mortality estimates based on a static natural history model (3) are expected to become less robust with further declines in measles incidence. To improve the estimation of global measles disease burden as measles incidence declines and to allow country-specific evaluations that can be used to modify measles mortality reduction strategies, WHO has developed a quasi-dynamic model, the measles strategic planning (MSP) tool. The MSP tool recently was reviewed by a WHO technical advisory group and was determined to be superior to the static model for estimating trends in measles mortality because the MSP tool uses 1-year instead of 5-year age groups and approximates the effect of herd immunity. After appropriate validation and adjustments have been made, the MSP tool will be used to generate annual estimates of global measles mortality beginning in 2008.
Although the WHO/UNICEF measles mortality reduction goal for 2005 was surpassed, major challenges exist to achieving the 2010 GIVS goal of 90% reduction in global measles mortality, and substantial work is required to sustain the gains already made. First, measles mortality reduction activities need to be implemented successfully in several countries with large populations and high measles burdens (e.g., India and Pakistan). Second, to sustain the gains in reduced measles deaths in the 47 priority countries, particularly in the Africa Region, vaccination programs need to be improved to ensure that >90% of infants are vaccinated against measles through routine health services before their first birthday. Third, all priority countries need to conduct follow-up SIAs every 2--4 years until their routine vaccination programs are capable of providing two opportunities for measles vaccination to >90% of all birth cohorts before age 5 years. Fourth, disease surveillance systems need to be strengthened at all levels to enable case-based surveillance with testing of clinical specimens from all suspected measles cases by laboratories participating in the global MRLN. Finally, measles case management, including appropriate vitamin A supplementation for all children with diagnosed measles cases (10), should be strengthened.
* Priority countries were selected on the basis of their contribution to the global measles disease burden: Afghanistan, Angola, Bangladesh, Benin, Burkina Faso, Burundi, Cambodia, Cameroon, Central African Republic, Chad, Congo, Côte d'Ivoire, Democratic Republic of the Congo, Djibouti, Equatorial Guinea, Eritrea, Ethiopia, Gabon, Ghana, Guinea, Guinea-Bissau, India, Indonesia, Kenya, Lao People's Democratic Republic, Liberia, Madagascar, Mali, Mozambique, Myanmar, Nepal, Niger, Nigeria, Pakistan, Papua New Guinea, Rwanda, Senegal, Sierra Leone, Somalia, Sudan, Timor-Leste, Togo, Uganda, United Republic of Tanzania, Vietnam, Yemen, and Zambia.
Any immunization activity implemented in addition to the routine immunization schedule. Measles SIAs are usually implemented as "catch-up" or "follow-up" mass immunization campaigns. A catch-up campaign includes a one-time initial vaccination conducted to achieve high population immunity rapidly and thereby interrupt chains of measles virus transmission. In countries aiming to reduce measles-associated mortality, an initial nationwide catch-up SIA usually targets all children aged 9 months--14 years. Follow-up campaigns generally are conducted nationwide every 2--4 years and target all children born since the previous campaign, usually those aged 9--59 months. Follow-up campaigns aim to eliminate any measles susceptibility that has built up in recent birth cohorts because of 1) suboptimal routine coverage with the first dose of measles vaccine and 2) a failure to develop an immune response after the first measles vaccination, which is expected in up to 15% of infants vaccinated at age 9 months.
§ Case-based surveillance includes investigation of every suspected measles case and routine reporting of detailed epidemiologic and laboratory data for each confirmed measles case.
¶ Additional information available at http://www.who.int/vaccines/globalsummary/immunization/countryprofileselect.cfm.
** Based on Monte Carlo simulations (3) that account for uncertainty in key input variables (e.g., vaccination coverage and case-fatality ratio).
Additional information available at http://www.measlesinitiative.org/index3.asp.
§§ Additional information available at http://www.gavialliance.org.
¶¶ Additional information available at http://www.iff-immunisation.org.
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Date last reviewed: 11/28/2007