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Measles Mortality Reduction --- West Africa, 1996--2002
The World Health Organization (WHO) estimates that, during 2000, measles accounted for approximately 777,000 deaths worldwide, of which 452,000 (58%) occurred in Africa (1). In response, in 2000, WHO's African Regional Office (AFRO) adopted a plan to reduce measles mortality >50% by 2005 (2). The plan recommended 1) increasing measles vaccination by strengthening routine health services; 2) providing a second opportunity for measles vaccination for all children, primarily through wide--age-range supplemental immunization activities (SIAs); 3) enhancing measles surveillance; and 4) improving management of measles cases. The initial wide--age-range SIA targets all children aged 9 months--14 years, regardless of history of measles disease or vaccination. Follow-up SIAs are needed 3--5 years after the initial SIA to provide a second opportunity for vaccination to children born since the previous SIA (i.e., those aged 9 months--4 years). During the 1990s, the countries of the Americas and seven countries in southern Africa used this strategy to reduce the number of measles deaths to near zero (3--5). This report describes the recent implementation of this strategy in three West African countries, where reported measles cases declined 83%--97% during the first year after SIAs. Successful implementation of this strategy by other African countries should result in achieving the goal of >50% reduction in measles mortality by 2005.
Routine and Supplemental Immunizations
In 2001, before use of wide--age-range SIAs, routine measles vaccination coverage was estimated to be 69% by the administrative method* in Burkina Faso, 37% by survey in Mali, and 33% by survey in Togo (WHO/United Nations Children's Fund [UNICEF], unpublished data, 2002). During December 2001--January 2002, nationwide SIAs among children aged 9 months--14 years were conducted to give a second opportunity for measles vaccination in these three countries.
A total of 12.7 million children were targeted in the three countries. National SIA coverage was estimated to be 95%--99% by survey method and 99%--104% by administrative method (Table 1). The number of reported measles cases and deaths has decreased 91% and 84%, respectively, compared with the annual averages for 1996--2001 (Table 1). The number of deaths averted was estimated by applying the observed percentage reduction in reported measles deaths in 2002, compared with the average annual number of deaths reported during 1996--2001, to the estimated number of measles deaths in 1998 (6) (Tables 1 and 2). WHO estimated the number of measles deaths in 1998 (before SIAs) by using the size of the surviving birth cohort, the reported vaccine coverage, vaccine efficacy, and a measles case-fatality ratio (CFR) of 6.0 (6).§ The estimated number of deaths averted in the three countries during 2002 was 26,365 (Table 2).
In 2002, surveillance for measles was enhanced by starting measles case-based surveillance with laboratory confirmation and intensifying supervision of all districts by provincial surveillance supervisors. According to regional guidelines, any clinician diagnosis of measles or illnesses consistent with the case definition of rash, fever, and cough, coryza, or conjunctivitis should be reported as suspected measles. In addition, all patients in whom measles is suspected should have blood collected for serologic confirmation.
In 2002, in Burkina Faso, blood specimens were taken for 1,060 (62%) of the 1,712 suspected cases. Of the 1,029 cases with laboratory results, 709 (69%) were measles-IgM positive. Of these, 255 (36%) cases were in persons aged >15 years. A total of 319 (45%) laboratory-confirmed cases occurred in the target age group for the SIAs (i.e., ages 9 months--14 years). In Mali, specimens were collected for 63 (12%) of 533 suspected measles cases; 22 (35%) tested measles-IgM positive. Laboratory-confirmed measles outbreaks were detected in one northern district among a nomadic population (n = 39) and in one district along the Guinea border (n = 36). During January 2001--December 2002, in Togo, specimens were collected from 250 (75%) of 333 suspected measles cases; 23 (9%) tested measles-IgM positive. Of these, 14 (61%) were in the northeastern province of Savane, and 11 (78%) were in the Tone district bordering Burkina Faso.
Reported by: Ministries of Health, Burkina Faso, Mali, and Togo; Country Offices for Burkina Faso, Mali, and Togo, World Health Organization. Measles Programme, Regional Office for Africa, World Health Organization, Harare, Zimbabwe. Global Immunization Div, National Immunization Program, CDC.
The measles mortality reduction strategies implemented in Burkina Faso, Mali, and Togo reduced the annual numbers of measles cases and deaths by 91% and 84%, respectively, during the first year after implementation of SIAs, compared with 6 years preceding SIAs. In 2002, an estimated 26,365 measles deaths were prevented. The Ministries of Health in Burkina Faso, Mali, and Togo were responsible for planning and conducting SIAs. Financial and technical support for implementing this strategy is being provided by a coalition of partners (The Measles Initiative) led by the American Red Cross; other partners include the United Nations Foundation, UNICEF, WHO, and CDC.
Although the reductions in cases and deaths in Burkina Faso were substantial compared with levels during 1996--2001, widespread measles transmission continued after the campaign. Widespread transmission after successful wide--age-range SIAs has not been reported in 13 other African countries (5; WHO, unpublished data, 2003). An outbreak investigation is under way to determine why the decline in cases in Burkina Faso was not as marked as in the other countries.
Remaining subjects of concern for the measles mortality reduction program include 1) the duration of effect of the wide--age-range SIAs, 2) the appropriate interval between the initial wide--age-range and subsequent SIAs, and 3) the best methods for increasing routine vaccination. On the basis of experience in the Americas and southern Africa, a 4-year interval between SIAs will maintain measles mortality at near zero if the routine measles coverage remains at >80% and the SIAs achieve coverage of >90% (3--6). However, attaining routine coverage of >80% will be challenging for these countries. From 1998--2000 to 2002, the reported routine coverage with the third dose of combined diphtheria-pertussis-tetanus vaccine (DPT3) increased in Mali, from 32%--53% to 74%; in Burkina Faso, from 34%--57% to 75%; and in Togo, from 36%--50% to 59% (WHO, unpublished data, 2003). The low routine measles vaccination coverage in these countries will result in accumulation of susceptible children born since the 2001 SIAs. This might result in small- to moderate-sized measles outbreaks before the scheduled follow-up SIAs planned for the fall of 2004.
The findings in this report are subject to at least two limitations. First, the decline in reported measles cases and deaths might be underestimated; <50% of serologic specimens, compared with >70% in countries with widespread measles transmission, drawn from patients with measles-compatible illnesses after SIAs in Mali and Togo were confirmed as measles on the basis of positive-IgM results. These findings are consistent with those observed in southern Africa after nationwide wide--age-range SIAs (5). Second, the estimated number of measles deaths before implementation of SIAs assumed no herd immunity and relied on available CFRs for measles (6). In the absence of recent population-based studies, these CFR estimates might have changed as a result of improvements in case management and a shift in the age distribution of patients. During 1989--1991, a population-based study in rural Ghana found a measles CFR of 15%, even in an area with vitamin A supplementation (7); this figure is substantially higher than the 6% CFR used to estimate the number of measles deaths averted.
During the next few years, improved surveillance for measles will be important to determine the effectiveness of the measles mortality reduction strategy. An increase in population immunity to measles decreases the positive predictive value of the clinical case definition (3,5), thereby necessitating laboratory confirmation of suspected cases. The implementation of case-based surveillance with serologic confirmation of suspected cases will require capacity for specimen collection, transportation, testing, and reporting of results. Previous experience with case-based surveillance, specimen collection, and testing for acute flaccid paralysis cases will guide this process.
* Calculated by dividing the number of doses of vaccine administered through routine health services by the birth cohort of the previous year.
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