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Abstract
Vaccination coverage is an important public health indicator that is measured using administrative reports and/or surveys. The measurement of vaccination coverage in low- and middle-income countries using surveys is susceptible to numerous challenges. These challenges include selection bias and information bias which cannot be solved by increasing the sample size and the precision of the coverage estimate which is determined by the survey sample size and sampling method. Selection bias can result from an inaccurate sampling frame or inappropriate field procedures and since populations likely to be missed in a vaccination coverage survey are also likely to be missed by vaccination teams most often inflates coverage estimates. Importantly the large multi-purpose household surveys that are often used to measure vaccination coverage have invested substantial effort to reduce selection bias. Information bias occurs when a childs vaccination status is misclassified due to mistakes on his or her vaccination record in data transcription in the way survey questions are presented or in the guardians recall of vaccination for children without a written record. There has been substantial reliance on the guardians recall in recent surveys and worryingly information bias may become more likely in the future as immunization schedules become more complex and variable. Finally some surveys assess immunity directly using serological assays. Sero-surveys are important for assessing public health risk but currently are unable to validate coverage estimates directly. To improve vaccination coverage estimates based on surveys we recommend that recording tools and practices should be improved and that surveys should incorporate best practices for design implementation and analysis.