Measuring the performance of vaccination programs using cross-sectional surveys: a likelihood framework and retrospective analysis.

Background: The performance of routine and supplemental immunization activities is usually measured by the

administrative method: dividing the number of doses distributed by the size of the target population. This method leads to

coverage estimates that are sometimes impossible (e.g., vaccination of 102% of the target population), and are generally

inconsistent with the proportion found to be vaccinated in Demographic and Health Surveys (DHS). We describe a method

that estimates the fraction of the population accessible to vaccination activities, as well as within-campaign inefficiencies,

thus providing a consistent estimate of vaccination coverage.

Methods and Findings: We developed a likelihood framework for estimating the effective coverage of vaccination

programs using cross-sectional surveys of vaccine coverage combined with administrative data. We applied our method to

measles vaccination in three African countries: Ghana, Madagascar, and Sierra Leone, using data from each country’s most

recent DHS survey and administrative coverage data reported to the World Health Organization. We estimate that 93% (95%

CI: 91, 94) of the population in Ghana was ever covered by any measles vaccination activity, 77% (95% CI: 78, 81) in

Madagascar, and 69% (95% CI: 67, 70) in Sierra Leone. ‘‘Within-activity’’ inefficiencies were estimated to be low in Ghana,

and higher in Sierra Leone and Madagascar. Our model successfully fits age-specific vaccination coverage levels seen in DHS

data, which differ markedly from those predicted by naı¨ve extrapolation from country-reported and World Health

Organization–adjusted vaccination coverage.

Conclusions: Combining administrative data with survey data substantially improves estimates of vaccination coverage.

Estimates of the inefficiency of past vaccination activities and the proportion not covered by any activity allow us to more

accurately predict the results of future activities and provide insight into the ways in which vaccination programs are failing

to meet their goals.