Progress Toward Global Measles Control and Elimination, 1990-1996

In 1989, the World Health Assembly resolved to reduce measles morbidity by 90% and measles mortality by 95% by 1995, compared with disease burden during the prevaccine era (1). By 1996, the estimated incidence and death rates for measles worldwide were reduced by 78% and 88%, respectively (2). In 1990, the World Summit for Children adopted a goal of vaccinating 90% of children against measles by 2000. However, routine measles vaccination coverage has remained relatively stable since 1990, and an estimated 1 million children continue to die from this preventable disease each year. During the 1990s, the widespread use of innovative measles-control strategies in the Region of the Americas and countries such as Mongolia, South Africa, and the United Kingdom demonstrated that high-level measles control and even interruption of transmission is feasible over large geographic areas. This report updates the status of measles control and elimination worldwide and includes disease surveillance and vaccination coverage data received by the World Health Organization (WHO) headquarters in Geneva, Switzerland, as of August 29, 1997. These findings indicate that, in some regions, substantial progress has been made to control and interrupt measles transmission; in others, measles continues to cause high morbidity and mortality because of failure to implement measles-control strategies. STAGES OF MEASLES CONTROL

Based on implementation of a combination of vaccination and surveillance strategies, countries are considered to be in one of three stages: control *, outbreak prevention, or elimination **. Measles Control

In the control stage, the objective is to achieve high routine coverage with one dose of measles vaccine among infants to reduce measles morbidity and mortality. To accelerate measles control in large urban and other high-risk areas with a substantial proportion of a country's unvaccinated children and measles deaths, mass vaccination campaigns targeting children aged 9 months to 3-5 years have been recommended (3). Measles Outbreak Prevention

Since the mid-1990s, an increasing number of countries where measles incidence has been persistently reduced have adopted aggressive vaccination strategies to prevent forecasted measles outbreaks or interrupt transmission completely. Administration of supplemental doses of measles vaccine through mass vaccination campaigns has resulted in high levels of population immunity and has interrupted transmission. In some countries, after the initial mass campaign, an additional dose of measles vaccine is recommended at school entry. Measles Elimination

In the Region of the Americas, the Pan American Sanitary Conference resolved in 1994 to eliminate measles from the Western Hemisphere by 2000 (4) using the following strategies: 1) conducting a one-time "catch-up" vaccination campaign targeting all children aged 9 months-14 years; 2) achieving and maintaining high routine measles vaccination coverage among children aged 12-23 months; 3) conducting periodic "follow-up" campaigns targeting all children aged 1-4 years; and 4) conducting enhanced surveillance with laboratory investigation of suspected cases (4). Other regions and countries have implemented or are considering implementation of strategies aimed at interrupting measles virus transmission. PROGRESS TOWARD IMPLEMENTING STRATEGIES Routine Vaccination Coverage

From 1977 (when the Expanded Program on Immunization began monitoring coverage) to 1990, global reported coverage with one dose of measles vaccine administered through routine services increased from approximately 5% in 1977 to 16% in 1983 and to 76% in 1990. Since 1990, routine measles vaccination coverage has remained relatively stable (Table_1), with reported coverage at 81% in 1996 (Figure_1). Comparing 1990 and 1996 data, reported routine vaccination coverage increased 3%-11% in the six WHO regions. In 1996, a total of 73 countries achieved coverage of greater than 90%. Nineteen countries reported coverage of less than 50%; of these, 16 were in Africa. To achieve global coverage of 90%, at least 14.3 million additional children need to be vaccinated each year, nearly 60% of whom reside in seven countries (Brazil, China, Ethiopia, India, Kenya, Nigeria, and Pakistan). Urban Vaccination Campaigns

During 1993-1996, several countries in Asia (Bangladesh, India, Myanmar, Nepal, and the Philippines) conducted urban vaccination campaigns targeting high-risk areas to reduce measles morbidity and mortality. However, surveillance data are insufficient to accurately assess the impact of these campaigns. Outbreak Prevention or Elimination Campaigns

During 1990-1996, a total of 49 countries conducted a catch-up vaccination campaign to interrupt measles transmission, administering measles vaccine to approximately 166 million children aged less than 18 years (93% of the population targeted). Approximately 142 million of these doses were administered in the Americas. In addition, 29 countries in the Americas conducted at least one follow-up campaign. Measles Surveillance

Establishment of measles surveillance remains a major challenge in both industrialized and developing countries. For example, measles is not a notifiable disease in Austria, France, Germany, and Japan. Even in countries where measles is notifiable, there is substantial underreporting of cases, and information about age and vaccination status of cases often is not collected.

In the Region of the Americas, measles surveillance has been strengthened substantially since 1990. A total of 43 (91%) countries have reported weekly to the regional office, and standardized case-based reporting of measles cases, including laboratory confirmation, has been established.

The reliability of clinical diagnosis of measles declines as the incidence of the disease decreases to very low levels. The current laboratory-confirmation strategy is based on a measles-specific immunoglobulin M (IgM) enzyme immunoassay (EIA) at national laboratories with confirmatory testing by IgM capture EIA at reference laboratories. In addition, a measles virus reference data bank is being established (5). Eight genotypes of measles virus have been identified worldwide. Additional measles isolates are needed to compile a global genotype map to facilitate tracking of virus transmission worldwide. IMPACT OF STRATEGY IMPLEMENTATION ON MEASLES INCIDENCE

During 1980-1996, the number of reported measles cases worldwide declined from 4.4 million in 1980 to 1.3 million in 1990 and to approximately 0.8 million in 1996. However, measles reporting is incomplete; the actual burden from measles in 1996 is an estimated 36.5 million cases and 1 million deaths (6). A total of 40 countries (representing 1% of the global population) reported zero measles cases in 1996, compared with 12 countries in 1990. These 40 countries primarily are small island nations in the Region of the Americas (23), the Western Pacific Region (nine), and the African Region (four).

In 1996, most (445,949 {62%}) of the measles cases worldwide were reported from the African Region (Table_1). Of the six WHO regions, disease burden in 1996 was lowest in the Americas (2109 cases); 488 (23%) cases were reported from the United States. This represented a 99% decline in number of cases in the region compared with 1990 and the lowest number ever reported by this region.

Reported by: Expanded Program on Immunization, Global Program for Vaccines and Immunization, World Health Organization, Geneva, Switzerland. Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Measles Activity, Epidemiology and Surveillance Div; Polio Eradication Activity, National Immunization Program, CDC.

Editorial Note

Editorial Note: Despite the widespread availability of safe and effective measles vaccines since 1963, measles still accounts for 10% of global mortality from all causes among children aged less than 5 years (6); it is the eighth leading cause of death worldwide, representing 2.7% of disability-adjusted life-years in 1990 (6). Failure to deliver at least one dose of measles vaccine to all infants continues to be the primary reason for this preventable morbidity and mortality.

As a result of ongoing progress toward global poliomyelitis eradication ***, increasing attention has been focused on improving measles control worldwide. In the Region of the Americas, the combination of conducting catch-up and follow-up vaccination campaigns and increasing routine vaccination coverage has demonstrated that measles transmission can be interrupted over large geographic areas (4). Although measles eradication is technically feasible (7), several programmatic, political, and financial obstacles must be overcome before such an eradication goal could be achieved. Polio eradication has stimulated acceleration of measles control worldwide and, in the European Region and the Eastern Mediterranean Region of WHO, has resulted in efforts to establish regional measles-elimination goals. Evaluation of elimination strategies in these regions and countries will provide valuable information for developing a global measles-eradication strategy.

Three immediate measures are necessary to attain disease-reduction and coverage goals and to decrease the number of deaths attributable to measles. First, countries should increase coverage with at least one dose of measles vaccine among infants, especially in countries in Sub-Saharan Africa, where a substantial number of measles deaths continue to occur each year. Second, more aggressive measles vaccination efforts are needed, including the use of mass campaigns in large urban and other high-risk areas (8). However, experience from countries such as Philippines (9) indicates that unvaccinated children frequently are missed by these campaigns unless special efforts are made to accurately identify the areas unreached by routine vaccination services. This experience emphasizes the need to develop the infrastructure necessary to provide routine vaccination services to these hard-to-reach communities. Third, surveillance must be strengthened as a critical component of accelerated measles control. Improved surveillance is necessary to evaluate the impact of strategies and to monitor the prevalence of susceptible persons in a population. When countries progress from measles-control to measles-elimination activities, surveillance must be sufficiently sensitive to rapidly detect importations of virus. As measles control accelerates and measles-elimination efforts are implemented, the diagnosis of measles will increasingly rely on laboratory confirmation. The establishment of a global measles laboratory network is essential for countries in the outbreak-prevention or measles-elimination stage.

Activities are ongoing to better estimate the global disease burden of measles, the cost and effectiveness of different control and elimination strategies, the interaction between measles elimination and polio eradication, and the benefits of measles eradication for development of health systems. However, these activities should not delay more immediate efforts to reduce the substantial disease burden caused by measles.

References

1. World Health Assembly. Executive summary. Geneva, Switzerland: World Health Organization, 1989; resolution no. WHA 42.32.

2. Global Program for Vaccines and Immunization. Progress toward 1995 measles control goals and implications for the future. Geneva, Switzerland: World Health Organization, 1996; publication no. WHO/GPV/SAGE 96.04.

3. Aylward BR, Clements J, Olive JM. The impact of immunization control activities on measles outbreaks in middle and low income countries. Intern J Epidemiol 1997;26:662-9.

4. de Quadros CA, Olive JM, Hersh BS, et al. Measles elimination in the Americas: evolving strategies. JAMA 1996;275:224-9.

5. Rota JS, Heath JL, Rota PA, et al. Molecular epidemiology of measles virus: identification of pathways of transmission and implications for measles elimination. J Infect Dis 1996;173:32-7.

6. Christopher JL, Lopez AD, ed. The global burden of disease: a comprehensive assessment of mortality and disability from diseases, injuries, and risk factors in 1990 and projected to 2020 -- summary. Geneva, Switzerland: World Health Organization, 1996:17-26.

7. CDC. Measles eradication: recommendations from a meeting cosponsored by the World Health Organization, the Pan American Health Organization, and CDC. MMWR 1997;46(no. RR-11).

8. Anonymous. Expanded programme on immunization -- accelerated measles strategies. Wkly Epidemiol Rec 1994;69:229-34.

9. Tangermann RH, Costales M, Flavier J. Poliomyelitis eradication and its impact on primary health care in the Philippines. J Infect Dis 1997;175(suppl 1):S272-S276.

* Reduction of disease incidence and/or prevalence to an acceptable level as a result of deliberate efforts, requiring continued control measures. 

** Reduction of the incidence of a disease to zero as a result of deliberate efforts, requiring continued control measures. 

*** Permanent reduction of the worldwide incidence of a disease to zero as a result of deliberate efforts, obviating the need for further control measures.

TABLE 1. Reported number of measles cases and reported measles vaccination coverage, by World Health Organization (WHO) region, 1990 and 1996 *
=================================================================================================================================================
                                           No. cases                                             Vaccination coverage
                         --------------------------------------------------          -------------------------------------------------------
Region                         1990       1996  % Change from 1990 to 1996           1990           1996   % Point change from 1990 to 1996
-------------------------------------------------------------------------------------------------------------------------------------------------
African                     481,294    445,949             - 7%                       53              56                  3%
American                    246,607      2,109             -99%                       77              85                  8%
Eastern Mediterranean        59,502     20,361             -66%                       76              85                  9%
European                    188,306    162,967             -13%                       80              86                  6%
Southeast Asian             225,144     81,477             -64%                       71              82                 11%
Western Pacific             156,139     84,459             -46%                       93              96                  3%

Total                     1,356,992    797,322             -41%                       76              81                  5%
-------------------------------------------------------------------------------------------------------------------------------------------------
* As reported to the WHO headquarters in Geneva, Switzerland, by August 29, 1997.
=================================================================================================================================================

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