Experience in Global Measles Control, 1990–2001

Ana-Maria Henao-Restrepo 2 Peter Strebel 4 Edward John Hoekstra 3 Maureen Birmingham 1 2 Julian Bilous 0 2 0 Expanded Programme on Immunizations, World Health Organization , Geneva , Switzerland 1 Vaccine Assessment and Monitoring 2 Department of Vaccines and Biologicals 3 Global Measles Programme, Health Section, Programme Division, United Nations Children's Fund , New York , New York 4 Global Measles Branch, Global Immunization Division, National Immunization Program, Centers for Disease Control and Prevention , Atlanta , Georgia Worldwide during the 1980s remarkable progress was made in controlling measles through increasing routine measles vaccination to nearly 80%. In 2000, an estimated 777,000 measles deaths occurred, of which 452,000 were in the African Region of the World Health Organization (WHO). In 2001, WHO and the United Nations Children's Fund published a 5-year strategic plan to reduce measles mortality by half by 2005. Strategies include providing a second opportunity for measles immunization to all children through nationwide supplementary immunization activities, increasing routine vaccination coverage, and improving surveillance with laboratory confirmation of suspected measles cases. In 2000, over 100 million children received a dose of measles vaccine through supplementary immunization activities, a number projected to increase during 2002-2005. Current systems for monitoring measles vaccination coverage and disease burden must be improved to accurately assess progress toward measles control goals. - WHO regions. The 214 countries and territories of the world, of which 191 are WHO member states, are divided into six WHO regions (figure 1). The global population in 2000 was 6.0 billion; the WHO regions in declining order of population are the Western Pacific (1.7 billion population), Southeast Asian (1.5 billion), European (0.9 billion), American (0.8 billion), African (0.6 billion), and Eastern Mediterranean (0.5 billion). Each country or territory is expected to report key health statistics annually to WHO. For measles vacci Geographic distribution of countries by WHO region, 2000 nation coverage and disease incidence, this is done through the WHO/United Nations Childrens Fund (UNICEF) joint reporting form. These reports are sent from each countrys ministry of health to the regional WHO office and then to WHO headquarters. Vaccination coverage. Measles vaccination coverage reported by countries and territories on the WHO/UNICEF joint reporting form reflects the first dose of vaccine given (mainly through routine immunization services) [5]. This is usually estimated by the administrative method, which is calculated as the number of doses of measles vaccine administered to infants through routine services during a year, divided by the birth cohort of the previous year. When coverage figures have not been reported to WHO headquarters, the WHO Vaccine Assessment and Monitoring group uses a statistical method to estimate the most likely coverage based on previous reports from the country or similar countries that have continued to report [5]. The method calculates a certainty range that reflects the influence of incomplete reporting on global and regional coverage. Because of problems determining the numerator and denominator for routine coverage by the administrative method, some countries conduct periodic national immunization coverage surveys and report these results to WHO. Many countries now provide a second opportunity for measles immunization through mass vaccination campaigns or have a routine second dose in the immunization schedule. WHO maintains a database S16 JID 2003:187 (Suppl 1) Henao-Restrepo et al. that includes information on measles mass campaigns conducted or planned. However, the coverage achieved at the second opportunity is often not reported to WHO. Morbidity. The annual total number of measles cases reported to WHO by countries and territories is usually a product of the routine communicable disease reporting system in each country. These numbers may be augmented by cases detected through outbreak investigations. In some countries measles is not a reportable disease and only data from sentinel surveillance systems are available; these countries often do not report national measles incidence to WHO [5]. Countries with a measles elimination goal, and several countries with mortality reduction goals, that have conducted mass measles campaigns have surveillance systems for rash and fever illness with laboratory confirmation of measles cases. These include all countries in the WHO Region of the Americas, seven southern African countries (South Africa, Botswana, Namibia, Zimbabwe, Malawi, Lesotho, and Swaziland), and selected countries in Asia, Europe, the Middle East, and Oceania [6]. Deaths occurring and prevented. The number of measles deaths in the prevaccine era were obtained from WHO estimates made in the early 1990s [3, 7]. Numbers of measles deaths by WHO region in 2000 were taken from a recent publication on the global burden of disease [4]. The number of measles deaths prevented in 2000 was estimated in two ways: first, by comparison with the prevaccine era (i.e., the number of deaths in the prevaccine era less the number of deaths in 2000 with the existing vaccination program) and second, by comparing an estimate of the number of deaths that would have occurred in the absence of a vaccination program in 2000 (i.e., the number of deaths that would occur in the absence of a vaccination program in 2000 less the number of deaths in 2000 with the existing vaccination program). To estimate the number of deaths that would have occurred in the absence of a vaccination program in 2000, we assumed that the age distribution of measles cases in 2000 in the absence of a vaccination program was the same as that observed in countries with low vaccination coverage (!80%) and that the measles case-fatality ratios by region in 2000 in the absence of a vaccination program were the same as those now occurring (i.e., those used by WHO to calculate the burden of measles disease in 2000 in the presence of the vaccination program) [8]. Routine coverage with one dose of measles vaccine. By 1982 virtually all countries had incorporated measles vaccine into their immunization programs. During the 1980s, there were widespread increases in routine coverage supported by the initiative for universal childhood immunization. Between 1990 and 2000, reported global routine vaccination coverage with one dose of measles vaccine among infants remained at about 80% (figure 2). However, coverage varied widely between regions and between countries within regions. The African Region reported the lowest coverage both in 1995 and in 2000 (table 1). Compared with 1995, the American, Eastern Mediterranean, and European regions reported increased measles vaccination coverage in 2000; the remaining three regions reported slight decreases (table 1). For each (...truncated)