Conducting a Statewide Population-Based Immunization Study: Lessons Learned

Background: Annually, since 1997, the Georgia Immunization Office has conducted the Georgia Immunization Study, a non-experimental retrospective cohort study, which determines the statewide and regional immunization coverage rates for two year old children born in the state of Georgia.  Prior to 2010, the study published both state and local aggregate coverage rates; however, the 2010 Final Report also presents odds ratios of adequate immunization coverage based on demographic factors.

Setting: The state of Georgia

Population: Two-year old children born in Georgia.  The annual study sample consists of a stratified random selection of approximately 2500 children.

Project Description: Immunization history data for the sample population were initially obtained from the Georgia Registry of Immunization Transactions and Services (GRITS).  For children found to be inadequately immunized (4:3:1:3:3:1:4 level), local health department staff contacted parents/guardians and private providers for additional information.  Once collected, immunization data were analyzed in conjunction with demographic variables obtained from the State Office of Vital Records.  The effect of socio-demographic characteristics on immunization coverage rates was assessed using multivariate logistic regression.

Results/Lessons Learned: Since the sample is population-based and the data collection process involves direct communication between public health staff, private providers, and parents, the immunization history data collected offer a reliable estimate of immunization coverage levels among the target population of two-year olds in Georgia.  While the National Immunization Study is a good source of interstate immunization data, this study reflects statewide and district immunization data that can be used by the Georgia Immunization Office to plan risk-based outreach campaigns on a state, district, or county level. In addition to coverage levels, these data provide an estimate of how complete GRITS data are relative to provider documentation.  [Data collection was concluded on October 29, 2010.  Final results will be available by January 1, 2011.]