Performance of small cluster surveys and the clustered LQAS design to estimate local-level vaccination coverage in Mali

We explored (i) the efficiency of cluster surveys of decreasing sample size through bootstrapping analysis and (ii) the performance of CLQAS under three alternative sampling plans to classify local VC, using data from a survey carried out in Mali after mass vaccination against meningococcal meningitis group A.VC estimates provided by a 10 × 15 cluster survey design were reasonably robust. We used them to classify health areas in three categories and guide mop-up activities: i) health areas not requiring supplemental activities; ii) health areas requiring additional vaccination; iii) health areas requiring further evaluation. As sample size decreased (from 10 × 15 to 10 × 3), standard error of VC and ICC estimates were increasingly unstable. Results of CLQAS simulations were not accurate for most health areas, with an overall risk of misclassification greater than 0.25 in one health area out of three. It was greater than 0.50 in one health area out of two under two of the three sampling plans.Small sample cluster surveys (10 × 15) are acceptably robust for classification of VC at local level. We do not recommend the CLQAS method as currently formulated for evaluating vaccination programmes.Vaccination coverage (VC) estimates are essential to monitor the performance of immunisation programmes and take action to improve them. In resource-poor settings, administrative estimates of VC, reached by dividing the number of people vaccinated by the population in the target age group, are often biased due to inaccurate population figures and pressure on programmes to report favourable indicators. Sample surveys are thus frequently employed to establish more accurate estimates.A specific challenge in these settings is estimation of VC at the local level (e.g. district, sub-district or health catchment area), so as to identify communities that may require additional support (e.g. supplementary campaigns, strengthening of routine vaccination) and allocate limited resources effici