Interaction of Socioeconomic Status and Provider Practices as Predictors of Immunization Coverage in Virginia Children

Objective. To describe the pattern of immunization in the cohort of children who entered public schools in Virginia in 1992. Design. This was a historic cohort study using stratified cluster sampling. Three strata were created based on the socioeconomic status (SES) of the children in the catchment area of each public school in Virginia. Setting. The random sample included public elementary schools throughout Virginia. Participants. Immunization records were obtained for a randomly selected cohort of 2519 first-grade children in Virginia. Outcome Measures. Age at completion of recommended childhood vaccines was determined from birth to school entry by SES, race, and population density. Provider practices were assessed by ascertaining missed opportunities for simultaneous administration of vaccinations according to recommended schedules. Results. Although immunization completion rates were high at school entry, low levels of immunization coverage were found in all areas of Virginia at 24 months of age regardless of SES (as measured by per capita income), population density, or race. However, under-immunization was more severe for poor children in urban areas (42.3% of children in low-SES urban areas were age-appropriately immunized at 24 months of age versus 64.0% in children in high-SES rural areas). By multivariate logistic regression, race and gender were not predictors of which children were appropriately immunized at 2 years of age after adjusting for the following: SES, population density, receiving the first DTP (diphtheria, tetanus, and pertussis) or OPV (oral polio) vaccination after 3 months of age, and failure to have the first DTP administered simultaneously with the first OPV or the second DTP administered simultaneously with the second OPV. Receiving the first DTP or OPV vaccination after 3 months of age and failure to have the first and second DTP and OPV administered simultaneously were the strongest predictors of not being age-appropriately immunized at 2 years of age. The effect of failure to vaccinate simultaneously on predicting vaccination coverage at 2 years of age was strongly modified by SES. Children who attended schools located in census tracts with per capita incomes less than $10 600 and who did not have the first and second doses of DTP and OPV administered simultaneously were 33.19 times more likely not to be age-appropriately immunized at 2 years of age compared with children who attended schools located in census tracts with per capita incomes greater than $18 800 and who received the first and second doses of DTP and OPV simultaneously (95% confidence interval: 18.29 to 60.22). Conclusions. Although beginning the immunization schedule at the recommended age was crucial to appropriate vaccination later in life, provider practices were important predictors of under-immunization. Failure to administer vaccinations simultaneously strongly influenced poorer children in Virginia. Serious delays in vaccine administration were observed not only for poor children in urban areas, but also in all areas of Virginia before school entry.