Estimating vaccination coverage: Routine information or sample survey?

The manager of a district immunization programme needs to regularly assess vaccination coverage. This case study from Zimbabwe describes how routine information can be used for this purpose. The number of children and their location in the district was estimated from several sources using a variety of methods. This suggested that under-enumeration at the 1982 census was probably as high as a third and was a particular problem among children aged under 1 year. Routinely collected figures of the number of vaccinations were then used to calculate coverage levels for different health unit catchment areas within the district. These levels varied considerably and were lowest in areas with significant numbers of Apostolics, a group who often reject immunization on religious grounds. Comparisons between estimates of coverage obtained from routine information and a sample cluster survey raised several issues. These included accuracy of routine information, precision of sample surveys, estimating differential coverage in the district, management uses of estimates and the cost of data collection.