Comparison of two survey methodologies to assess vaccination coverage.

Vaccination coverage surveys - Publication

abstract: BACKGROUND: Measuring vaccination coverage permits

evaluation and appropriate targeting of vaccination services. The

cluster survey methodology developed by the World Health

Organization, known as the \'Expanded Program on Immunization (EPI)

methodology\', has been used worldwide to assess vaccination

coverage; however, the manner in which households are selected has

been criticized by survey statisticians as lacking methodological

rigor and introducing bias. METHODS: Thirty clusters were selected

from an urban (Ambo) and a rural (Yaya-Gulelena D/Libanos) district

of Ethiopia; vaccination coverage surveys were conducted using both

EPI sampling and systematic random sampling (SystRS) of households.

Chi-square tests were used to compare results from the two

methodologies; relative feasibility of the sampling methodologies

was assessed. RESULTS: Vaccination coverage from a recent measles

campaign among children aged 6 months through 14 years was high:

95% in Ambo (both methodologies), 91 and 94% (SystRS and EPI

sampling, respectively, P-value = 0.05) in Yaya-Gulelena D/Libanos.

Coverage with routine vaccinations among children aged 12-23 months

was <20% in both districts; in Ambo, EPI sampling produced

consistently higher estimates of routine coverage than SystRS.

Differences between the two methods were found in demographic

characteristics and recent health histories. Average time required

to complete a cluster was 16h for EPI sampling and 17 h for SystRS;

total cost was equivalent. Interviewers reported slightly more

difficulty conducting SystRS. CONCLUSIONS: Because of the

methodological advantages and demonstrated feasibility, SystRS

would be preferred to EPI sampling in most situations. Validating

results in additional settings is recommended.