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Global Measles Control and Regional Elimination, 1998-1999
In 1989, the World Health Assembly adopted the goal of reducing measles morbidity and mortality by 90% and 95%, respectively, by 1995, compared with estimates of the disease burden in the prevaccine era (1). In 1990, the World Summit for Children adopted a goal of vaccinating 90% of children against measles by 2000. Three regions of the World Health Organization (WHO) have targeted elimination: in 1994, the American Region (AMR) targeted elimination by 2000; in 1997, the Eastern Mediterranean Region (EMR) targeted elimination by 2010; and in 1998, the European Region (EUR) targeted elimination by 2007. This report updates progress since 1997 (2) toward global measles control and regional elimination of measles, and includes vaccination coverage and disease surveillance data received by WHO as of August 14, 1999. Data for 1998 suggest that routine measles vaccination coverage has declined in some regions, the number of countries reporting cases and coverage to WHO has decreased, and measles continues to be an important cause of morbidity and mortality.
Reported Routine Measles Vaccination Coverage
Global reported coverage with one dose of measles vaccine declined from 79% in 1997 to 72% in 1998 (Table 1). In 1998, 14 countries reported measles coverage below 50%: 10 in the African Region (AFR) (Burundi, Cameroon, Central African Republic, Chad, Democratic Republic of Congo, Ethiopia, Liberia, Nigeria, Togo, and Uganda), one in AMR (Haiti), two in EMR (Afghanistan and Somalia), and one in the South-East Asia Region (SEAR) (Democratic People's Republic of Korea).
Among regions focusing on measles control, AFR and SEAR reported the lowest routine vaccination coverage rates, 49% and 67%, respectively (Table 1). These regions reported the greatest decrease in coverage during 1997-1998. The Western Pacific Region (WPR) continued to report the highest routine vaccination coverage (93%).
Among regions with an elimination target, AMR reported the highest coverage rate (86%) (Table 1). In EMR, regional measles vaccination coverage was 78%, and 14 polio-free countries that began implementing measles elimination strategies reported routine coverage rates greater than 85% (3). EUR reported a routine first dose coverage rate of 71% in 1998; 21 (41%) of 51 EUR countries* did not report vaccination coverage data to WHO.
Supplementary Vaccination Campaigns
Supplemental vaccination campaigns have been conducted in several countries targeting either measles morbidity and mortality reduction or elimination. In 1998 and 1999, 31 countries in AFR** and three countries in EMR (Djibouti, Egypt, and Sudan) conducted mass vaccination campaigns in high-risk areas to reduce morbidity and mortality among those children who were not vaccinated through routine vaccination services. During 1998-1999, two countries (Marshall Islands and Palau) in WPR conducted vaccination campaigns targeting children who had not been vaccinated through routine vaccination services, two countries (Lao People's Democratic Republic and Viet Nam) delivered measles vaccination to remote populations during polio subnational immunization days, and one country (Viet Nam) conducted a pilot campaign in one province.
WHO's measles elimination strategy comprises a three-part vaccination strategy (i.e., "catch-up," "keep-up," and "follow-up"***); two parts are supplemental vaccination (4). All countries in AMR, except the United States and the French and Dutch Antilles, completed catch-up campaigns by 1996. Since then, most countries in AMR have been conducting follow-up campaigns.
In nine of 15 EMR countries where measles elimination activities are ongoing, 13 million children have been vaccinated during catch-up measles vaccination campaigns conducted since 1994 (3). In EUR, Romania implemented a catch-up campaign during 1998-1999 targeting all children aged 7-18 years (girls aged 15-18 years received measles and rubella vaccine). Approximately 2 million children were vaccinated and 93% coverage was reported (WHO, unpublished data, 1999). During 1998-1999, staff from 23 (45%) of 51 countries**** in EUR attended workshops at which they evaluated their age-specific susceptibility to measles and determined strategies to reduce susceptibility to less than 15% for ages 0-4 years, less than 10% for ages 5-9 years, and less than 5% for ages greater than or equal to 10 years (5).
Since 1995, 23 million children have been vaccinated during catch-up campaigns in the six southern African nations where measles-elimination initiatives have been launched (6). In addition, United Kingdom (1994), Bhutan (1995), the Maldives (1995), Mongolia (1996), Papua New Guinea (1997), New Zealand (1997), Australia (1998), parts of China (1997-1998), the Philippines (1998), and 13 Pacific island countries and areas (since 1997) conducted catch-up campaigns.
Reported and Estimated Measles Morbidity and Mortality
Among regions with measles elimination goals, the AMR reported the lowest incidence (1.6 per 100,000) in 1998 (Table 2). The measles outbreak that began in Brazil in 1997 affecting unvaccinated adults continued in 1998 and 1999 among unvaccinated young children in Argentina, Bolivia, Colombia, the Dominican Republic, and Paraguay. As of November 27, 1999, 2698 measles cases have been confirmed in the region compared with 10,067 cases for the same period in 1998. During 1997-1998 in EMR, the number of cases reported increased by 58%; outbreaks were reported in Iran, Syria, Morocco, and Saudi Arabia. In EUR, the number of cases reported declined 59%, but the number of countries reporting measles cases declined from 45 in 1997 to 31 in 1998. Among all regions, AFR reported the highest number of measles cases and incidence. Of all the cases reported, more than half were reported from countries in AFR.
Each year, WHO estimates actual measles morbidity and mortality; because measles is not a notifiable disease in some countries, substantial underreporting of measles occurs, and measles deaths are not reported to WHO. For 1998, WHO estimated that approximately 30 million measles cases and 888,000 measles-related deaths occurred worldwide; an estimated 85% of the measles-related deaths occurred in AFR and SEAR (7).
Global Measles Laboratory Network
Efforts are under way to establish a Global Measles Laboratory Network. Measles laboratories of CDC and the Central Public Laboratory Services in the United Kingdom have been selected as the Global Measles Strain Banks. Activities to strengthen laboratory capacity to support measles surveillance include assessment of country laboratory needs, training of laboratory staff, provision of diagnostic kits, and collection of specimens for diagnosis and virus isolation. During 1998-1999, eight measles laboratory workshops were conducted, and 105 laboratory staff from 42 countries in five regions were trained in basic measles diagnostic methods.
Reported by: Vaccines and Biologicals Dept, World Health Organization, Geneva, Switzerland. Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Epidemiology and Surveillance Div; Vaccine Preventable Disease Eradication Div, National Immunization Program; and an EIS Officer, CDC.
With approximately 1 million deaths attributed to measles in 1998, measles remains an important cause of vaccine-preventable illness and death. Failure to deliver at least one dose of measles vaccine to all infants remains the primary reason, despite widespread availability of an effective and safe vaccine. Morbidity and mortality decrease with increasing vaccination coverage levels; those regions with the lowest coverage levels have the highest burden, with AFR continuing to report both the lowest coverage and highest incidence.
Global and regional (except AMR) routine vaccination coverage rates in 1997 and 1998 were calculated using model-based estimates to account for missing data (8). Nationwide surveys indicated that in some countries actual coverage may be lower than reported coverage (9). For this reason, some countries in SEAR (Bangladesh, India, and Indonesia) have begun reporting coverage based on surveys rather than the administrative method. In part, this change in reporting accounts for the decline in reported coverage in SEAR in 1998. Although some regions (e.g., WPR) may have achieved the World Summit for Children goal, coverage in some WPR countries and in the remaining five regions is less than 90%. Reported regional routine vaccination coverage rates in the three regions with measles elimination goals are less than 90%, thus increasing the speed at which susceptible children accumulate and the need for more frequent follow-up campaigns to prevent re-emergence of measles (10). Further improvements in routine vaccination coverage and methods used to monitor it are needed to decrease the morbidity and mortality associated with measles.
During 1997-1998, the number of countries reporting vaccination coverage or measles cases decreased in some regions. EUR had the highest proportion of regional population from which data were not reported. Strengthening of measles surveillance is required in both developed and developing countries to monitor progress toward achieving morbidity and mortality reduction or regional elimination goals. All countries should improve routine reporting of measles cases by month of occurrence and geopolitical unit. Countries should use outbreak investigations to obtain data on age and vaccination status of persons with measles and to estimate population-based case-fatality ratios. Case-based surveillance with laboratory confirmation of suspected measles cases and virus isolation from all outbreaks are needed when incidence of measles decreases to low levels following implementation of measles elimination measures. The global measles laboratory network needs to be strengthened by WHO, especially in those countries with elimination goals, by recruiting additional laboratories and compiling standard procedures for testing of samples.
Reduced measles incidence under conditions of improved surveillance suggests substantial progress in AMR toward achieving the regional measles elimination goal. Recent resurgence of measles in this region emphasizes the importance of full and timely implementation of elimination strategies. In EMR, routine vaccination coverage and surveillance need to be further strengthened throughout the region. Appropriate vaccination strategies for elimination need to be implemented to reduce susceptibility to measles in countries of EUR. Lack of reporting from some of the western European countries impairs assessment of disease burden and coverage in the region and suggests an urgent need to improve measles surveillance and to monitor vaccination coverage.
The priorities for countries pursuing accelerated measles control include improving routine vaccination coverage levels to at least 80% in all districts of every country, achieving at least 90% coverage nationwide, conducting supplementary vaccination campaigns together with administration of vitamin A in high-risk areas, and improving completeness and timeliness of reporting of measles cases at district level. Priorities for countries and regions with a measles elimination goal include improving routine vaccination coverage levels to at least 90% in all districts of every country (resulting in nationwide coverage greater than or equal to 95%); achieving coverage greater than 90% in catch-up and follow-up campaigns or achieving nationwide coverage greater than or equal to 95% with a routine second dose of measles vaccine, and establishing case-based surveillance with laboratory confirmation of suspected cases and virus isolation from all chains of transmission. Adherence to these priorities will ensure that the measles morbidity and mortality burden will decrease and that the measles disease reduction targets can be reached.
* Andorra, Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Luxembourg, Monaco, Norway, Poland, San Marino, Spain, Sweden, Switzerland, the former Yugoslav Republic of Macedonia, Turkey, and Yugoslavia.
** Angola, Benin, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Congo, Côte d'Ivoire, Democratic Republic of Congo, Equatorial Guinea, Eritrea, Ethiopia, Gabon, Ghana, Guinea, Kenya, Liberia, Madagascar, Mali, Mauritania, Mozambique, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, Togo, Uganda, United Republic of Tanzania, and Zambia.
*** "Catch-up" is a one-time, nationwide vaccination campaign targeting usually all children aged 9 months-14 years, regardless of history of measles disease or vaccination status; "keep-up" is routine services aimed at vaccinating 95% of each successive birth cohort; and "follow-up" is subsequent nationwide vaccination campaigns conducted every 2-5 years targeting usually all children born after the catch-up campaign.
**** Andorra, Bulgaria, Croatia, Czech Republic, Denmark, Germany, Greece, Hungary, Italy, Kazakhstan, Kyrgyzstan, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Switzerland, Tajikistan, Turkmenistan, and Uzbekistan.
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TABLE 1. Reported routine measles vaccination* coverage among children aged 1 year, by World Health Organization (WHO) region -- worldwide, 1997 and 1998
* One dose of measles-containing vaccine (MCV).
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TABLE 2. Reported measles cases and a comparison of measles surveillance, by World Health Organization (WHO) region -- worldwide, 1997 and 1998*
* Reported to WHO as of August 14, 1999.
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