Measuring coverage in MNCH: design- implementation- and interpretation challenges associated with tracking vaccination coverage using household surveys.


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 child's 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 guardian's recall of vaccination for children without a written record. There has been substantial reliance on the guardian's 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.