Measles resurgence in southern Africa: challenges to measles elimination

Abstract

Introduction: In seven southern African countries (Botswana, Lesotho, Malawi, Namibia, South Africa, Swaziland and Zimbabwe), following implementation of a measles mortality reduction strategy starting in 1996, the number of annually reported measles cases decreased sharply to less than one per million population during 2006-2008. However, during 2009-2010, large outbreaks occurred in these countries. In 2011, a goal for measles elimination by 2020 was set in the World Health Organization (WHO) African Region (AFR). We reviewed the implementation of the measles control strategy and measles epidemiology during the resurgence in the seven southern African countries.

Methods: Estimated coverage with routine measles vaccination, supplemental immunization activities (SIA), annually reported measles cases by country, and measles surveillance and laboratory data were analyzed using descriptive analysis.

Results: In the seven countries, coverage with the routine first dose of measles-containing vaccine (MCV1) decreased from 80% to 65% during 1996-2004, then increased to 84% in 2011; during 1996-2011, 79,696,523 people were reached with measles vaccination during 45 SIAs. Annually reported measles cases decreased from 61,160 cases to 60 cases and measles incidence decreased to <1 case per million during 1996-2008. During 2009-2010, large outbreaks that included cases among older children and adults were reported in all seven countries, starting in South Africa and Namibia in mid-2009 and in the other five countries by early 2010. The measles virus genotype detected was predominantly genotype B3.

Conclusion: The measles resurgence highlighted challenges to achieving measles elimination in AFR by 2020. To achieve this goal, high two-dose measles vaccine coverage by strengthening routine immunization systems and conducting timely SIAs targeting expanded age groups, potentially including young adults, and maintaining outbreak preparedness to rapidly respond to outbreaks will be needed.

Keywords: Africa; Elimination; Immunization; Measles; Vaccination.

Fig. 1.

Reported measles cases*, estimated coverage** with the routine first dose of measles-containing vaccine (MCV1), and measles supplemental immunization activities*** (SIAs), seven southern African countries, 1996–2011. *Measles cases reported annually to WHO by member states through the WHO/UNICEF Joint Reporting Form. **Population-weighted average using United Nations Development Programme population estimates and annual national WHO/UNICEF MCV1 coverage estimates for children aged 1 year for 1996–2011 ***In each country, measles SIAs started with an initial catch-up SIA targeting all children aged 9 months to 14 years and then periodic follow-up SIAs, generally targeting all children born since the last SIA, conducted nationwide every 2–4 years targeting children aged 9–59 months, in some cases, expanded age groups were used in follow-up SIAs.

Fig. 2.

Confirmed* measles cases by epidemiological week, seven southern African countries, 2009 (N = 9546), 2010 (N = 111,186), and 2011 (N = 267). *Confirmed measles cases were defined by laboratory confirmation, epidemiological link, or classified as clinically compatible. Note: In 2009, 33 cases in Namibia had missing date data. In 2010, 23,548 cases in Malawi had missing date data. M: months, Y: years, ORI: Outbreak response immunization campaign, SIA: supplemental immunization activity. ^aSub-national ORI campaign in response to the outbreak conducted in September–November 2009, target age 5–19Y, 77% coverage achieved. ^bSub-national ORI campaign in response to the outbreak conducted in October–November 2009, target age 5–19Y, 88% coverage achieved. ^cNational planned SIA with expanded age group in response to the outbreak conducted in May–July 2010, target age 6M–15Y, 98% coverage achieved. ^dSub-national ORI campaigns in response to the outbreak conducted September–December 2009 in 6 districts, target age 6–59M, coverage achieved NA. ^eSub-national ORI campaigns in response to the outbreak conducted in February–March 2010 in 4 districts, target age 6–59M in 3 districts, >6M in 1 district, irrespective of previous vaccination status, coverage range by district 88–115%. ^fNational ORI campaign in response to the outbreak conducted in May 2010, target age 6M-14Y, 97% coverage achieved. ^gNational campaign conducted in November 2009, target age 9–59M, 115% coverage achieved. ^hNational planned SIA with expanded age group in response to the outbreak conducted in September 2010, target age 6M–15Y, 91% coverage achieved. ⁱNational planned SIA with expanded age group in response to the outbreak conducted in August 2010, target age 9M–15Y, 107% coverage achieved. ^jNational campaign conducted in October–November 2010, target age 9–59M, 90% coverage achieved.

Fig. 3.

Annualized reported confirmed measles incidence* and measles virus genotypes detected by district, seven southern African countries, 2009–2011. *Annualized reported measles incidence was calculated by dividing the number of reported confirmed measles cases from national measles case-based surveillance data by annual population estimates from national census projections. Note: Each genotype symbol on the map indicates between 1 and 37 specimens of that genotype in a district.