Volume 28-10
15 May 2002

[Table of Contents]

INTERNATIONAL NOTE

GLOBAL MEASLES MORTALITY REDUCTION AND REGIONAL ELIMINATION, 2000-2001

Despite the widespread availability of measles vaccine for nearly 40 years, measles remains a major cause of childhood mortality. There were an estimated 30 to 40 million cases of measles in 2000, causing some 777,000 deaths. Measles thus accounts for nearly one-half of the 1.7 million annual deaths due to childhood vaccine- preventable diseases (Figure 1). Measles remains a leading cause of childhood mortality worldwide, accounting for 5% of all deaths among children < 5 years of age.

In 2001, World Health Organization (WHO) and United Nations Children's Fund (UNICEF) developed a Global Measles Strategic Plan 2001-2005, together with the United States Centers for Disease Control and Prevention (CDC) and numerous experts worldwide, and in coordination with several other partners. The objectives of the plan include: (i) halving the annual number of measles deaths by 2005; (ii) achieving and maintaining interruption of indigenous measles transmission in large geographic areas with established elimination goals (the Region of the Americas by 2000 [nearly achieved], the European Region by 2007, and the Eastern Mediterranean Region by 2010); and (iii) convening a global consultation in 2005, in collaboration with other major partners, to review progress and assess the feasibility of global measles eradication.

Figure 1: Causes of vaccine-preventable deaths among children < 15 years, 2000*
* Total: 1,756,350

Four complementary strategies are required to achieve sustainable measles mortality reduction:

1) Provide the first dose of measles vaccine to successive groups of all children at 9 months of age or shortly thereafter.

2) Guarantee a "second opportunity" for measles vaccination to all children, either through campaigns or routine immunization. The second opportunity is needed both to increase the chance that every child receives at least one dose of measles vaccine, and to increase the proportion of the population that is fully immunized. When the first dose is given at 9 months of age, not all children will develop a protective response. The second dose, given later, will increase the protective response and the likelihood of immunity. Countries with high vaccination coverage and a system to follow defaulters are able to implement a two-dose measles vaccination schedule. Countries unable to develop a two-dose schedule with high coverage should conduct supplementary campaigns aimed at children in the highest mortality group (i.e., < 5 years of age), but can extend to older age groups with a high proportion of susceptibles (e.g., 5 to 10 or 5 to 15 years of age) if they are important sources of infection for young children. Ideally, campaigns should target large populations (entire nations or large regions) and achieve coverage of > 90% with safe and high-quality services.

3) Establish an effective system to monitor coverage and conduct measles surveillance with integration of epidemiologic and laboratory information.

4) Improve management of every measles case, including vitamin A supplementation. In addition, the plan includes a recommendation to integrate vitamin A supplementation, and rubella vaccine and surveillance, with measles vaccination and surveillance activities, where appropriate.

This article updates data from 1999-2001 on measles mortality reduction and regional elimination, and includes vaccination coverage and disease surveillance data received by WHO as of October 2001.

Reported routine measles vaccination coverage

Between 1990 and 2000, reported global routine vaccination coverage with one dose of measles vaccine among infants remained at approximately 80%. The number of countries providing data on measles coverage and incidence has dropped in the past 3 years, particularly in the European Region and in the Americas. In 2000, only 128 (approximately 70% of the population) out of the 214 Member countries and territories reported to WHO. In 2000, an estimated 115 million doses of measles vaccine were administered through routine immunization services.

Among regions focusing on measles mortality reduction, the African and South-East Asia regions reported the lowest routine vaccination coverage rates, 55% (47% to 59%) and 83% (83% to 84%), respectively. The Western Pacific Region continued to report the highest routine vaccination coverage, 86% (24% to 97%).

Among regions with an elimination goal, the Americas reported a measles coverage rate of 91% (83% to 92%). In the Eastern Mediterranean, regional measles vaccination coverage was 79% (73% to 82%), and 18 countries implementing measles elimination strategies reported routine coverage rates above 80%. Europe reported a routine first-dose coverage rate of 92% (59% to 96%) in 2000.

In 2000, 16 countries (Afghanistan, Central African Republic, Chad, Congo, Democratic Republic of the Congo, Equatorial Guinea, Ethiopia, Gabon, Kenya, Lao People's Democratic Republic, Nauru, Niger, Nigeria, Senegal, Sierra Leone, Togo) reported routine measles vaccination coverage of < 50%. No measles coverage data were received for 2000 from Angola, Cameroon, Guinea-Bissau and Somalia; all reported measles coverage < 50% in 1999. Only 74 countries (35%) reported measles coverage levels > 90%.

Second opportunity for measles immunization

By 2000, only 52 of 214 (24%) countries or territories had a routine measles vaccination schedule consisting of a single dose at 9 months of age. All remaining countries had either provided a second opportunity for measles vaccination through supplementary nationwide campaigns during the preceding 3 years, or a routine two-dose schedule. In general, countries with a single-dose policy are the poorest and least developed countries, report the lowest routine vaccination coverage, and experience the highest measles disease burden.

Supplementary vaccination campaigns have been conducted in several countries targeting either mortality reduction or measles elimination. In 2001, seven countries in Africa*, one country in the Eastern Mediterranean (Yemen), one country in South-East Asia (Bangladesh) and three countries in the Western Pacific (Cambodia, Lao People's Democratic Republic, Viet Nam) conducted mass vaccination campaigns to reduce mortality, reaching children who were not vaccinated through routine immunization services. During these campaigns, approximately 25 million children were immunized.

In 1999-2000, 90 million children in 35 African countries were reached with vitamin A supplementation during campaigns (polio or measles). In addition, countries have adopted strategies for improving measles case management through the integrated management of childhood illness (IMCI) approach.

In 1994, the ministers of health of all Member countries in the Americas set the goal of regionwide measles elimination by 2000. Under the leadership of the Pan American Health Organization (PAHO), aggressive vaccination activities have been undertaken in all countries of the region. All countries, except the United States (U.S.), French Guiana and several Caribbean islands, had completed catch-up campaigns by 1996. Since then, all countries in the region have conducted follow-up campaigns**.

Selected countries in southern Africa, Asia, Europe, the Middle East and Oceania have adopted immunization strategies aimed at measles elimination. Substantial progress in interrupting measles transmission has been achieved in these countries.

Since 1994, catch-up measles vaccination campaigns have been conducted in 11^† out of 18 countries of the Eastern Mediterranean where measles elimination activities are ongoing. In recent years, supplementary mass national campaigns have been undertaken in four European countries: the United Kingdom (1994), Romania (1999), Albania (2000) and most recently Kyrgyzstan (2001).

Since 1995, nearly 25 million children have been vaccinated during catch-up campaigns in the seven*** southern African nations where measles-elimination initiatives have been launched. Between 1998 and 2001, catch-up campaigns have been conducted in Australia, China (Hong Kong Special Administrative Region), New Zealand, the Philippines and other Pacific island nations. Mongolia conducted a follow-up campaign in 2000.

Reported and estimated measles morbidity and mortality

Globally, 817,161 measles cases were reported in 2000; however, substantial underreporting exists and disease surveillance remains weak and underfunded in many countries. Regional and country variations in reported incidence can be explained by changes in surveillance performance, reporting artifacts and measles outbreaks.

In the Americas, countries that have adequately implemented all of the PAHO/WHO recommended strategies have successfully interrupted measles transmission. As of December 2001, 469 cases of measles have been confirmed in the region compared with 1,764 cases for the same period in 1999; 72% of cases occurred in three countries (Dominican Republic, Haiti and Venezuela). Similarly, importation of measles cases from Latin America into the U.S. decreased from 242 in 1990 to zero in 2000.

In countries of southern Africa, the number of reported measles cases has dropped dramatically, from > 50,000 per year before the catch-up campaigns to 100 cases in 1999. Measles deaths have decreased, from an estimated 3,700 deaths before the catch-up campaigns to two in 1999 and zero deaths in 2000.

In the Eastern Mediterranean, 50% of the 34,971 measles cases reported in 2000 occurred in countries in the measles elimination stage, most of them from countries that have not yet conducted the initial catch-up campaign (Islamic Republic of Iran, Libyan Arab Jamahiriya and Morocco).

During the past decade, the reported number of measles cases in the European Region has fallen from approximately 300,000 in 1991 to 36,306 in 2000, although outbreaks have been reported from a number of countries. However, the sensitivity of the national surveillance systems ranges from sentinel to national case-based reporting systems. Furthermore, laboratory confirmation practice varies across the region. This high variability is partly related to the different levels of measles control across the region.

Reduction in the number of cases and measles deaths has been documented in countries implementing high-quality mass campaigns for measles mortality reduction in the African, Eastern Mediterranean and Western Pacific regions, and elsewhere.

Each year, WHO estimates actual measles morbidity and mortality, because: 1) measles is not a notifiable disease in some countries; 2) substantial underreporting of measles occurs in some regions; and 3) measles deaths are not reported to WHO. Remarkable progress has been made in controlling measles through vaccination. Worldwide, measles vaccine prevents an estimated 80 million measles cases and 4.5 million measles deaths annually. For 2000, WHO estimated that approximately 30 to 40 million measles cases and 777,000 measles-related deaths occurred worldwide. The majority (> 90%) of the measles-related deaths are estimated to occur in Africa and South-East Asia.

Measles surveillance and laboratory network

Currently, most countries with a measles elimination goal that have conducted the initial catch-up campaign are implementing measles case-based surveillance with laboratory confirmation. These include all countries in the Region of the Americas, seven in countries of southern Africa, and selected countries in Asia, Europe, the Middle East and Oceania.

In addition, countries in the measles mortality reduction stage have enhanced efforts to improve their understanding of measles epidemiology (age and vaccination status of cases) through routine reports, hospital record reviews and outbreak investigations. At the end of 2001, countries in Africa that have achieved low measles incidence (e.g., Benin, Burkina Faso, Mali and Togo) switched to case-based measles surveillance; six other African countries will initiate case-based measles surveillance between January and June 2002 as part of an integrated disease surveillance approach.

Integrated acute flaccid paralysis, measles and neonatal tetanus surveillance has been successfully implemented in a number of countries in the Eastern Mediterranean. In recent years, countries in the Western Pacific (e.g., Cambodia, China, Philippines, Lao People's Democratic Republic, Viet Nam and some Pacific island countries) have implemented activities designed to enhance existing measles surveillance systems. Plans are under way to improve the quality of surveillance systems in South-East Asia using experience with acute flaccid paralysis surveillance.

Efforts are ongoing to establish a global measles laboratory network, using the experience of the global polio laboratory network. Measles laboratories of the CDC and the central public laboratory services in the United Kingdom have been selected as the global measles strain banks. Regional and national measles laboratories have been identified in most regions and a number of countries. Since 1998, measles laboratory workshops have been conducted and staff from > 50 countries in all regions were trained in basic measles diagnostic methods.

WER Editorial note

The major reason for the ongoing measles disease burden is underutilization of measles vaccine, both low coverage with the first dose and lack of a second opportunity for measles vaccination. Most measles deaths can be prevented by using existing vaccine and immunization strategies, and by ensuring more efficient use of available immunization services. The priority for the next 4 years is to achieve sustainable measles mortality reduction.

Those regions with the lowest coverage levels with the first dose and lack of a second opportunity for measles immunization experience the highest burden, with Africa continuing to report both the lowest coverage rates and the highest incidence.

Nationwide surveys indicate that in some countries actual coverage may be lower than reported coverage. Further improvements in routine vaccination coverage and methods used to monitor it are needed to achieve and sustain a reduction in the disease and death burden associated with measles.

The broader benefits of measles mortality reduction need to be further identified, including the synergies with overall routine immunization, disease surveillance, other health interventions and the strengthening of health systems. Specific activities and indicators should be developed and monitored in each area.

To achieve sustainable measles mortality reduction, countries are encouraged to do the following:

• Assess progress in measles control and review their measles epidemiology.
• Develop a 3- to 5-year plan for measles mortality reduction. Countries should develop plans together with the national inter-agency coordinating committees. Measles plans should be part of a comprehensive plan for strengthening immunization services.
• Identify the reasons for low routine coverage. Special attention should be given to districts with the lowest levels of coverage. A further argument for improving routine coverage is that if conducted, supplementary measles campaigns will then be effective in preventing measles deaths over a longer period of time.
• Take advantage of the priority given to measles to improve immunization safety. The safety of immunization is based on ensuring that the following elements are addressed: behavioural change, the provision of safe injection equipment (e.g., auto-disable syringes and safety boxes) and the adequate management and disposal of immunization waste.
• Plan and integrate measles activities with other health initiatives as appropriate. This will widen the scope and improve the impact of the public health care system.
• Use advocacy for measles mortality reduction to promote the further development of routine immunization services.

The strengthening of measles surveillance is required in both developed and developing countries to monitor progress towards achieving 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 measles cases and estimate population-based case-fatality ratios. Case-based epidemiologic and virologic data are needed when the incidence of measles decreases to low levels following the implementation of intensive measles immunization strategies. The global measles laboratory network needs to be further strengthened, especially in those countries with elimination goals, by recruiting additional laboratories and compiling standard procedures for testing samples.

Recent surveillance data indicate that in some countries an increasingly important proportion of the cases occur in children > 5 years of age, highlighting the need to obtain reliable information on measles epidemiology in each country, and to adjust immunization strategies accordingly.

In 2002, an additional 17 African countries (Benin, Cameroon, Côte d'Ivoire, Democratic Republic of the Congo, Ghana, Guinea, Kenya, Lesotho, Liberia, Malawi, Rwanda, Senegal, Swaziland, Uganda, United Republic of Tanzania, Zambia, Zimbabwe) are planning measles mass campaigns targeting 75 million children for vaccination. Similar efforts are under way in 30 countries in other regions targeting nearly 260 million children in 2002.

Reduced measles incidence under conditions of improved surveillance suggests substantial progress in the Americas towards achieving the regional measles elimination goal.

Developments in global immunization offer new opportunities to further reduce measles mortality worldwide. New resources have been mobilized for measles mortality reduction in Africa by a partnership facilitated by the American Red Cross. The Global Alliance for Vaccines and Immunization (GAVI) is attracting new financial support (e.g., from the Bill and Melinda Gates Foundation and the United Nations Foundation) and political support for immunization. GAVI support for immunization infrastructure aimed at achieving at least 80% vaccination coverage for the third dose of diphtheria, tetanus and pertussis (DTP3) vaccine will lead to increases in measles vaccination coverage, and in turn, improved measles mortality reduction.

Many experts believe that global eradication is technically feasible. The lessons learned from the regions with measles elimination goals (Americas, Eastern Mediterranean and Europe) will be invaluable for providing information on the feasibility of a future global eradication goal. However, additional information and experience are required before the benefits of a measles eradication goal can be properly assessed. The WHO Steering Committee on Measles Research has developed a measles research agenda. This agenda has helped to direct research into the barriers to effective measles mortality reduction and elimination. Firstly, it will be important to document the incremental costs, cost-effectiveness and opportunity costs of different measles control goals. Political support for different goals should be assessed and reliable information obtained on all operational and technical issues, including immunization safety concerns, effective strategies for interrupting transmission in densely populated urban centres in Africa and Asia, and the need for improved routes of administration of measles vaccine, as well as the impact of the human immunodeficiency virus pandemic on measles control.

Source: WHO Weekly Epidemiological Record, Vol 77, Nos 7 and 8, 2002.

* WHO's measles elimination strategy has three essential immunization components. Firstly, a one-time national "catch-up" campaign targeting all children in age groups where most susceptibles have accumulated, irrespective of previous disease or vaccination history. Secondly, efforts are made to strengthen routine immunization efforts to reach at least 95% of infants in each successive birth cohort ("keep-up"). Thirdly, "follow-up" campaigns (occurring once every 3 to 4 years) aim to vaccinate all children born since the previous campaign. The frequency of the follow-up campaigns depends on the effectiveness of the vaccine and the coverage of the routine program.

** Bahrain, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, Syrian Arab Republic, Tunisia, United Arab Emirates, West Bank and Gaza Strip.

† Botswana, Lesotho, Malawi, Namibia, South Africa, Swaziland and Zimbabwe.

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