Validating child vaccination status in a demographic surveillance system using data from a clinical cohort study: evidence from rural South Africa.

BACKGROUND: Childhood vaccination coverage can be estimated from a range of sources. This study aims to validate vaccination data from a longitudinal population-based demographic surveillance system (DSS) against data from a clinical cohort study. METHODS: The sample includes 821 children in the Vertical Transmission cohort Study (VTS)- who were born between December 2001 and April 2005- and were matched to the Africa Centre DSS- in northern KwaZulu-Natal. Vaccination information in the surveillance was collected retrospectively- using standardized questionnaires during bi-annual household visits- when the child was 12 to 23 months of age. DSS vaccination information was based on extraction from a vaccination card or- if the card was not available- on maternal recall. In the VTS- vaccination data was collected at scheduled maternal and child clinic visits when a study nurse administered child vaccinations. We estimated the sensitivity of the surveillance in detecting vaccinations conducted as part of the VTS