Abstract
BackgroundChildhood 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.MethodsThe 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 during these clinic visits.ResultsVaccination data in matched children in the DSS was based on the vaccination card in about two-thirds of the cases and on maternal recall in about one-third. The sensitivity of the vaccination variables in the surveillance was high for all vaccines based on either information from a South African Road-to-Health (RTH) card (0.94-0.97) or maternal recall (0.94-0.98). Addition of maternal recall to the RTH card information had little effect on the sensitivity of the surveillance variable (0.95-0.97). The estimates of sensitivity did not vary significantly, when we stratified the analyses by maternal antenatal HIV status. Addition of maternal recall of vaccination status of the child to the RTH card information significantly increased the proportion of children known to be vaccinated across all vaccines in the DSS.ConclusionMaternal recall performs well in identifying vaccinated children aged 12-23 months (both in HIV-infected and HIV-uninfected mothers), with sensitivity similar to information extracted from vaccination cards. Information based on both maternal recall and vaccination cards should be used if the aim is to use surveillance data to identify children who received a vaccination.
Highlights
Childhood vaccination coverage can be estimated from a range of sources
Maternal antenatal HIV status was available for 819 children, of whom 405 (50%) were HIV infected
The proportion of all children in the Vertical Transmission cohort Study (VTS) who received vaccinations on the scheduled study visit date was highest for Polio1 (86%, 95% confidence interval (CI) 84-88) and lowest for Hepatitis B3 vaccine (48%, 95% CI 45-52)
Summary
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. Between 2000 and 2007, child deaths from measles declined by an estimated 74% globally and 89% in Africa; polio, a major cause of disability and morbidity among children, is close to eradication [4]. This success is largely due to the Expanded Programme of Immunization (EPI) which. Two methods to estimate vaccination coverage in young children are commonly used: administrative data, which are unreliable if the target population is poorly enumerated, and may overestimate coverage [7]; and cross-sectional population-based surveys which determine the percentage of children vaccinated within a certain geographic area, such as the demographic and health surveys (DHSs) [8]. Vaccination data, collected from the mother (or another household member, if the mother is absent), on all children aged 12-23 months at the time of the interview are used in calculating coverage
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