Progress Toward Measles Control --- African Region, 2001--2008

Progress Toward Measles Control --- African Region, 2001--2008

In 2001, the countries of the World Health Organization (WHO) African Region (AFR) became part of a global initiative with a goal of reducing the number of measles deaths by 50% by 2005, compared with 1999. Recommended strategies for measles mortality reduction included 1) increasing routine coverage for the first dose of measles-containing vaccine (MCV1) for all children, 2) providing a second opportunity for measles vaccination through supplemental immunization activities (SIAs), 3) improving measles case management, and 4) establishing case-based surveillance with laboratory confirmation of all suspected measles cases (1). Before introduction of MCV throughout AFR, approximately 1 million measles cases had been reported each year in the early 1980s (2). After strengthening measles-control activities, annual reported cases declined to an estimated 300,000--580,000 during the 1990s. This report summarizes the progress made during 2001--2008 toward improving measles control in AFR. During 2001--2008 estimated MCV1 coverage increased from 57% to 73%, SIAs vaccinated approximately 398 million children, and reported measles cases decreased by 93%, from 492,116 in 2001 to 32,278 in 2008. By 2005, global measles deaths had decreased by 60%, and the AFR goal had been achieved (3); AFR adopted a new goal to reduce deaths by 90%, compared with 2000, and that goal was achieved in 2006 (3,4). However, inaccuracies in reported vaccination coverage exist, surveillance is suboptimal, and measles outbreaks continue to occur in AFR countries. Further progress in measles control will require full implementation of recommended strategies, including validation of vaccination coverage.

Since the 1980s, AFR countries have reported measles vaccination coverage and the number of measles cases each year to the WHO African Regional Office (AFRO), using the WHO and United Nations Children's Fund (UNICEF) Joint Reporting Form. These data are collected through administrative reports from routine vaccination programs and SIAs and routine surveillance systems that provide aggregated case counts based on clinical diagnosis. Estimates of routine coverage with MCV1 are based on review of coverage data from administrative records, surveys, national reports, and consultation with local and regional experts. Coverage achieved during nationwide SIAs against measles are reported on the basis of the reported number of doses administered, divided by the target population.

In 1999, as part of the measles mortality reduction strategy, case-based surveillance with laboratory testing for all suspected measles cases was introduced with support from WHO AFRO. A suspected measles case is defined as 1) any person with generalized maculo-papular rash and fever plus cough or coryza or conjunctivitis or 2) any person in whom a clinician suspects measles. Each suspected measles case should be reported using an individual case-investigation form, and a blood specimen should be collected and sent to the laboratory for measles-specific immunoglobulin M testing. Laboratory confirmation of individual cases is discontinued after an outbreak has been confirmed as measles. An outbreak is confirmed when three or more measles laboratory-confirmed cases are detected in a health facility or district in 1 month; subsequent cases are confirmed by epidemiologic link. An epidemiologic link is defined as a suspected measles case that did not have a specimen collected for laboratory testing and is linked in person, place, and time to a laboratory-confirmed case (i.e., in a patient living in the same district or an adjacent district with a patient with laboratory-confirmed measles where a likelihood of transmission and onset of rash in the two patients within 30 days of each other exists) (5). Case-based surveillance data from AFR countries are shared regularly with WHO AFRO. Data quality is monitored using annualized performance indicators that include the 1) percentage of districts reporting one or more suspected case with a blood specimen (target: >80%) and 2) nonmeasles febrile rash illness rate (target: >2 cases per 100,000).

Routine Vaccination Activities

In AFR, MCV1 is administered through routine services to children at age 9 months. According to WHO and UNICEF estimates, AFR MCV1 coverage increased from 57% in 2001 to 73% in 2008 (Figure). In 2008, among the 46 AFR countries,* three (7%) had MCV1 coverage of <60%, 13 (28%) had coverage of 60%--69%, 11 (24%) had coverage of 70--79%, 10 (22%) had coverage of 80--89%, and nine (20%) had coverage of ≥90% (Table 1). As of 2008, five (10%) countries provided a second dose of MCV (MCV2) through routine services: South Africa and Swaziland reported MCV2 coverage of 70%, Lesotho reported MCV2 coverage of 80%, and Algeria and Seychelles reported MCV2 coverage of >95% in 2008.

SIA Results

SIAs provide a second opportunity for measles immunization to all children, including those not vaccinated with MCV1 and those previously vaccinated; approximately 15% of children vaccinated with a single dose at age 9 months will not develop immunity to measles. The SIA strategy generally consists of a one-time catch-up SIA, targeted to a wide age range, which aims to reduce susceptibility to measles in the population. This is followed by periodic follow-up SIAs targeting children born since the last SIA, thus reducing the accumulation of susceptible children in new birth cohorts.

Before 2000, seven (15%) AFR countries (Botswana, Lesotho, Malawi, Namibia, South Africa, Swaziland, and Zimbabwe) had completed a catch-up SIA, and Namibia and South Africa had completed a follow-up SIA (6). By the end of 2008, 43 AFR countries (all except Algeria, Mauritius, and Seychelles) had completed a catch-up SIA, and all but Comoros and Guinea-Bissau had completed at least one follow-up SIA (Table 2). During 2001--2008, approximately 398 million children were vaccinated during measles SIAs in AFR: 237 million (60%) during catch-up SIAs in 34 countries, and 161 million (40%) during follow-up SIAs in 39 countries (Table 2). Nine countries (Benin, Cameroon, Chad, the Democratic Republic of Congo, Ethiopia, Ghana, Niger, Nigeria, and Tanzania) conducted nationwide SIAs in phases covering different geographic areas implemented over ≥2 years.

Measles Surveillance

By December 2008, all AFR countries except Algeria, Comoros, Guinea Bissau, Mauritius, Sao Tome & Principe, and Seychelles had established measles case-based surveillance in accordance with the WHO AFRO measles surveillance guidelines (5). In 2008, of the 40 countries with case-based surveillance, 21 (53%) met the target of >80% of districts reporting one or more suspected cases; 24 (60%) had a nonmeasles febrile rash illness rate of >2 cases per 100,000 population; and 16 (40%) met both targets.

Monitoring Measles Incidence

Following implementation of the measles mortality reduction strategies during 2001--2008, including introduction of case-based measles surveillance, the number of reported measles cases decreased 93%, from 492,116 in 2001 to 32,278 in 2008 (Figure). Average annual measles incidence in AFR decreased 66%, from 50.2 per 100,000 population during 2001--2004 to 17.2 during 2005--2008 (Table 1). Despite this decrease, during 2005--2008, 14 countries† reported outbreaks. Outbreak field investigations conducted during 2003--2007 in South Africa (1,676 cases, 2003--2005) (7), Kenya (2,544 cases, 2005--2007) (8), and Tanzania (1,533 cases, 2006--2007) (9) found that failure to vaccinate was the primary cause. In 2008, outbreaks also contributed to annual case counts in Burkina Faso (395), Cameroon (495), the Democratic Republic of Congo (12,461), Ethiopia (3,511), Niger (1,317), and Nigeria (9,960) (2).

Reported by: Countries in the World Health Organization African Region; Immunization and Vaccine Development, World Health Organization Regional Office for Africa. Dept of Immunization, Vaccines, and Biologicals, World Health Organization, Geneva, Switzerland. Global Immunization Div, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note:
In 2008, after implementation of the measles mortality reduction strategy, routine measles vaccination coverage in AFR reached 73%, SIAs were conducted in nearly all AFR countries, and reported measles cases decreased to a historic low of 32,278. According to previously published WHO estimates, by 2006 AFR had achieved approximately 90% reduction in measles deaths, compared with 2000 (3). However, despite this progress, vaccination coverage reports remain imprecise, disease surveillance remains suboptimal, and outbreaks continue to occur, even in countries that reported implementation of all recommended components of the measles strategy. Available mathematical models likely overestimate the disease burden and underreporting of measles cases is common, even with high-performing surveillance systems; therefore, caution is recommended when drawing comparisons between reported incidence of measles and estimates of measles deaths generated from models.

SIAs are recommended to provide a second opportunity for immunization and increase the likelihood of vaccinating hard-to-reach children. SIA coverage usually is estimated by an administrative method relying on the reported number of vaccine doses administered and available target population denominator data, both of which often are imprecise. For example, during 2001--2008, several countries reported vaccinating >100% of children targets in SIAs. Improved methods for determining the actual target population size for SIAs are needed; reported coverage also should be routinely validated by independent surveys. In addition, detailed field investigations of outbreaks should be undertaken to identify post-SIA risk factors for measles, and help refine vaccination strategies.

The findings in this report are subject to at least two limitations. First, a change in measles surveillance methods might result in underestimates or overestimates of the disease burden over time. For example, in 1999, AFR countries routinely reported an aggregated number of clinically diagnosed measles cases; however, after implementation of measles case-based surveillance, by 2005, most countries had changed to reporting laboratory-confirmed measles cases (6). Second, although the case definition for suspected measles remained the same, the change in measles reporting practices might have led to either underreporting, because of the additional resources needed to complete individual case investigations and collect blood samples, or overreporting because of overall efforts to strengthen measles surveillance.

In light of progress made toward reducing measles deaths, a more advanced goal was proposed recently for the region with several recommendations to improve vaccination coverage and surveillance performance. The AFR measles technical advisory group met in May 2008 and recommended that AFR countries aim to meet the following targets by 2012: 1) reducing estimated measles deaths by 98%, compared with 2000 estimates; 2) reducing measles incidence to < 5 cases per 1 million population per year; 3) achieving ≥90% routine MCV1 coverage nationwide and >80% in all districts; 4) achieving >95% SIA coverage in all districts; and 5) attaining two primary measles surveillance performance indicator targets (a nonmeasles febrile rash illness rate of >2 cases per 100,000 population per year and one or more suspected measles case investigated with blood specimen in >80% of districts per year); and 6) routine reporting from all districts (10). The group also recommended that AFR countries consider introduction of MCV2 in the routine vaccination schedule if MCV1 coverage of >80% has been achieved and maintained for ≥3 consecutive years and at least one of the two primary measles surveillance indicator targets has been achieved and maintained for at least 2 years. For countries adopting a 2-dose routine measles vaccination schedule, continued follow-up SIAs were recommended for all new birth cohorts every 3--5 years until national MCV2 coverage of ≥90% is sustained for at least 2 years (10).

References
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World Health Organization, Regional Office for Africa. Regional strategic plan for the expanded programme on immunization, 2006--2009. Available at http://www.afro.who.int/cah/documents/epi/afro_rc56_epi_sep_2006.pdf.
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* Algeria, Angola, Benin, Botswana, Burkina Faso, Burundi, Cameroon, Cape Verde, Central African Republic, Chad, Comoros, Congo, Côte d'Ivoire, Democratic Republic of Congo, Equatorial Guinea, Eritrea, Ethiopia, Gabon, Gambia, Ghana, Guinea, Guinea-Bissau, Kenya, Lesotho, Liberia, Madagascar, Malawi, Mali, Mauritania, Mauritius, Mozambique, Namibia, Niger, Nigeria, Rwanda, Sao Tome and Principe, Senegal, Seychelles, Sierra Leone, South Africa, Swaziland, Togo, Uganda, United Republic of Tanzania, Zambia, and Zimbabwe.

† Angola, Benin, Burkina Faso, Cameroon, Democratic Republic of Congo, Equatorial Guinea, Ethiopia, Kenya, Mali, Niger, Nigeria, South Africa, Tanzania, and Uganda.

FIGURE. Number of reported measles cases* and coverage with the first dose of measles-containing vaccine (MCV1) among children aged <1 year† --- World Health Organization (WHO) African Region, 2001--2008 (ver acceso debajo/please see below)

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Progress Toward Measles Control --- African Region, 2001--2008