Changing epidemiology of measles in Africa

Abstract

Background: In Africa before the introduction of measles vaccination, measles primarily affected young children. To describe measles epidemiology in Africa since the start of accelerated measles control activities in 2001, we analyzed regional measles case-based surveillance data for 2002-2009.

Methods: Country-years were grouped by 10-year moving average of routine measles vaccination coverage (aMCV1). Age was log transformed, and pair-wise comparisons of means were made. A χ(2) test was used to assess association between coverage and age groups. Cumulative percent curves and percentiles of age, dot plots with Loess curve, and Spearman rank correlation coefficient were calculated.

Results: Of 180,284 suspected cases, 73,009 (41%) were confirmed as measles. Of these, the mean age was 79 months (median, 36 months; interquartile range, 16-96 months) and significantly younger in country-years with <50% aMCV1 than those with 50%-74% aMCV1 (P=.03) and ≥75% (P=.02). With increasing coverage, there was a slight decrease in age in the 10th and 25th and moderate increase in age in the 50th, 75th, and 90th percentiles.

Conclusions: During 2002-2009, the median age of confirmed measles was 36 months. In countries with ≥50% aMCV1 coverage compared with low-coverage countries, age shifted to older children and young adults; for infants, age decreased slightly with higher coverage.