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Progress Toward Measles Elimination -- Southern Africa, 1996-1998

Despite routine measles vaccination coverage of greater than 70% in southern Africa during the early 1990s, low-level endemic transmission and periodic epidemics of measles continued. Since 1995, six southern African nations (Botswana, Malawi, Namibia, South Africa, Swaziland, and Zimbabwe) have launched measles-elimination initiatives in accordance with the recommendations of the World Health Organization (WHO) African Regional Office (AFR) (1). Strategies include programs to 1) achieve routine vaccination coverage of greater than or equal to 95% with one dose of measles vaccine administered at age 9 months; 2) implement a one-time national catch-up* measles vaccination campaign to interrupt indigenous transmission of measles; 3) implement periodic national follow-up** measles campaigns to maintain interruption of measles transmission; and 4) establish case-based measles surveillance with laboratory confirmation (2 ). This report presents preliminary data about the progress toward measles elimination in the six southern Africa countries.

Campaigns in each country were planned and implemented by national ministries of health with technical assistance from AFR. The South African government funded its measles campaign. In the other countries, campaigns received primary support from the national governments, the United Kingdom Department for International Development, the United Nations Children's Fund (UNICEF), WHO, and CDC. The campaigns emphasized safe injection practices, safe disposal of used injection equipment, and monitoring for adverse events following vaccination. All countries used disposable syringes and packed used equipment in disposal boxes for incineration or deep burial.

Because the number of qualified vaccinators was limited, particularly in countries where National Immunization Days (NIDs) for poliomyelitis were ongoing, national catch-up measles campaigns were divided into phases by geographic area or target population. The national measles campaign in South Africa was combined with polio NIDs and conducted in 1996 and 1997. Three of nine provinces conducted campaigns in both years, targeting children aged 9 months-4 years during 1996 and children aged 5-14 years during 1997 (Table 1), and the remaining six provinces targeted all children aged 9 months-14 years in a single campaign. Botswana divided the campaign geographically, covering approximately half the districts in 1997 and the remaining districts in 1998. In Swaziland, children aged 9 months-4 years were targeted in the catch-up campaign in 1998 in combination with polio NIDs followed by a second phase for children aged 5-14 years scheduled for May 1999. The remaining three countries--Malawi, Namibia, and Zimbabwe--completed the catch-up campaign in 1 year.

A total of 23 million children were vaccinated during the catch-up campaigns. Overall, reported coverage was 92% in the six countries (range: 85%-114%) (Table 1). Namibia and South Africa conducted additional mopping-up*** vaccination activities in 1997 in districts where initial coverage was less than 70%. No deaths or cases with persisting sequelae associated with vaccination were reported. In Zimbabwe, four children died within 30 days after vaccination; however, independent review of the case histories of these four children determined that none of the deaths were attributable to vaccination (N. Halsey, The Johns Hopkins University, personal communication, 1998).

During 1980-1989, when routine measles vaccination was being introduced in Botswana, South Africa, Swaziland, and Zimbabwe, the average annual number of reported measles deaths was 544 (range: 299-1089). During 1990-1996 in these four countries, when routine coverage was greater than 70%, the average annual number of measles deaths was 118 (range: 59-183). Measles mortality data were not reported routinely during 1980-1989 in Malawi and Namibia. To calculate measles morbidity and mortality reduction after the catch-up campaigns, data from Malawi were excluded because its campaign was conducted in October 1998, after the peak measles season had occurred. Following the implementation of measles catch-up vaccination campaigns in the remaining five countries, the number of reported measles cases decreased by 93% (Figure 1); 56,123 cases were reported by the five countries in 1996, compared with 3672 cases in 1998. Reported measles-associated deaths decreased 99%, from 166 in 1996 to two in 1998.

Since completion of catch-up vaccination campaigns, case-based surveillance of suspected measles cases has been initiated in four of the six countries, using the WHO case definition (i.e., any case with rash and fever and at least one of the following symptoms: cough, coryza, or conjunctivitis). Following training for national laboratory technicians of the six countries in July 1998, laboratory capacity to investigate suspected measles cases using a measles IgM enzyme-linked immunoassay (ELISA) was introduced in four countries. Because of the limited availability of measles IgM ELISA kits, serum was tested from 425 (14%) of the 3035 persons with suspected measles in Botswana, Namibia, South Africa, and Zimbabwe since the catch-up campaigns. Of 425 suspected measles cases tested, 17 (4%) were measles IgM-positive (Table 2). In South Africa, of the 275 measles IgM-negative serum samples that were tested for rubella IgM, 140 (46%) were positive.

Reported by: Ministries of health of Botswana, Namibia, and Swaziland. Ministry of Health and Population, Malawi. Dept of Health, South Africa. Ministry of Health and Child Welfare, Zimbabwe. WHO African Regional Office, Harare, Zimbabwe; Vaccines and Other Biologicals Dept, World Health Organization, Geneva, Switzerland. Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, and Vaccine Preventable Disease Eradication Div, National Immunization Program, CDC.

Editorial Note:

Despite the availability of a safe and effective vaccine since 1963, measles still accounts for nearly 1 million deaths annually (3). In 1990, the World Summit for Children adopted the goal of vaccinating 90% of children against measles by 2000. Regional measles elimination goals have been established in the Americas (by 2000), Europe (by 2007), and the Eastern Mediterranean (by 2010) (3).

The six countries described in this report achieved and sustained routine vaccination coverage of approximately 80% before initiation of measles elimination campaigns. Routine vaccination had a substantial impact on measles epidemiology: measles morbidity declined, the interval between epidemics was lengthened, the average age of patients increased, and measles mortality was reduced to low levels. As a result of these conditions and successful polio eradication strategies, measles elimination campaigns were initiated in the six countries.

High vaccination coverage was achieved during the mass campaigns in the six countries. Reported campaign coverage may overestimate true coverage (e.g., in countries reporting coverage of greater than 100%) because children outside the target age range who were vaccinated in the campaign were included in the numerator or the target population was underestimated.

The catch-up vaccination campaigns have been highly effective in reducing morbidity and mortality resulting from measles in the six countries. Since the campaigns were completed, none of the 70 suspected measles cases tested in Botswana and Zimbabwe was laboratory-confirmed, suggesting that measles transmission in those countries may have been interrupted. Circulation of measles virus has been reduced to very low levels in Namibia and South Africa.

To sustain the elimination initiative, the six southern African countries will need to continue to implement all WHO-recommended strategies. First, to increase routine vaccination coverage to greater than or equal to 95%, these countries should eliminate missed opportunities for vaccination, introduce tracking systems to find children who miss appointments for vaccination, and strengthen outreach services to reach communities not routinely covered. Second, epidemiologic analysis of measles cases and data about district-specific routine and catch-up measles vaccination coverage will help ministries monitor the accumulation of susceptible persons in the population and plan appropriate follow-up vaccination campaigns. Finally, case-based surveillance of suspected measles cases should be strengthened. A serum specimen should be obtained for measles IgM testing from at least five patients in each outbreak and from 80% of persons with sporadic cases; specimens should be obtained at the time the patient first seeks health care. In addition, measles virus for each outbreak should be isolated to distinguish importations of measles virus from ongoing indigenous transmission (4).

Experience from the Americas has highlighted the need to ensure that all WHO-recommended strategies are fully implemented (5). To sustain progress toward measles elimination in southern Africa, continued national commitment to support and implement WHO strategies is needed to prevent the re-establishment of measles transmission, and possibly to avoid large outbreaks, in countries where elimination has been achieved.

References

  1. World Health Organization. Acceleration of measles mortality reduction and measles elimination in the African Region: five-year plan of action, 1999-2003. Harare, Zimbabwe: World Health Organization, Regional Office for Africa, 1998.
  2. De Quadros CA, Olive JM, Hersh BS, et al. Measles elimination in the Americas: evolving strategies. JAMA 1996;275:224-9.
  3. CDC. Progress toward global measles control and regional elimination, 1990-1997. MMWR 1998;47:1049-54.
  4. Pan American Health Organization. Measles eradication field guide. Washington, DC: Pan American Health Organization, Pan American Sanitary Bureau, Regional Office of the World Health Organization, 1998. (Technical paper no. 41).
  5. Pan American Health Organization. Expanded program on immunization in the Americas: good surveillance is key to measles eradication. EPI Newsletter 1999;21:3-4.

* Catch-up is a one-time, nationwide vaccination campaign targeting all children, usually those aged 9 months-14 years, regardless of history of measles or vaccination.

** Follow-up campaigns are subsequent nationwide vaccination campaigns conducted every 2-5 years targeting all children born after the catch-up campaign, usually those aged 9 months-4 years.

*** In this context, "mopping-up" vaccination is intended to increase coverage in pockets of low coverage occurring during "catch-up" or "follow-up" campaigns; vaccination preferably should be conducted house-to-house.



Table 1



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TABLE 1. Routine measles vaccination coverage, 1996, and vaccination coverage
during nationwide measles "catch-up" vaccination campaigns, 1996-1998 -- six
southern African countries
=================================================================================================
                 Routine    Dates of     Target age      Target         No.       Vaccination
Country         coverage    campaign       group       Population   vaccinated     coverage
---------------------------------------------------------------------------------------------
South Africa
  4 provinces      --         8/96      9 mos-14 yrs    3,559,252    3,317,400        93%
  3 provinces      --         8/96      9 mos- 4 yrs    2,173,753    1,786,048        82%
  3 provinces*     --         5/97      5 yrs-14 yrs    4,045,498    3,495,415        86%
  2 provinces      --         5/97      9 mos-14 yrs    4,278,598    3,281,321        77%
  Total           82%+                                 14,057,101   11,880,184        85%

Botswana
  14 districts              7-8/97&     9 mos-14 yrs      344,280      347,265       101%
   8 districts               5/98&      9 mos-14 yrs      234,960      246,420       105%
  Total            82%                                    579,240      593,685       102%

Namibia            61%        6/97      9 mos-14 yrs      737,977      677,538        92%
Zimbabwe           77%        6/98      9 mos-14 yrs    5,279,248    4,929,475        93%
Swaziland          70%        6/98      9 mos-59 mos      147,545      146,626        99%
Malawi             90%       10/98      9 mos-14 yrs    4,179,229    4,747,452       114%

Total                                                  24,980,340   22,974,960        92%
---------------------------------------------------------------------------------------------
* Same three provinces that conducted campaigns in August 1996 for children aged 9 months-
  4 years.
+ Coverage based on a survey in 1998.
& Fourteen of 22 districts conducted the campaign in 1997 and the remaining eight districts in
  1998.
=================================================================================================

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Figure 1

Figure 1
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Table 2



Note: To print large tables and graphs users may have to change their printer settings to landscape and use a small font size.

TABLE 2. Number of reported measles cases, number tested, and number and
percentage positive following catch-up vaccination campaigns -- four southern
African countries, 1997-1998
===============================================================================
                                          IgM-positive
               No. reported               ------------
Country           cases       No. tested    No.   (%)
------------------------------------------------------
Botswana            469            21         0    --
Namibia            1795            48         4   (8)
South Africa        331           307        13   (4)
Zimbabwe            440            49         0    --
Total              3035           425        17   (4)
------------------------------------------------------
===============================================================================


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