Prevalence and predictors of immunization among inner-city infants: A birth cohort study

Context. Although the proportion of US children who are appropriately immun ized increased dramatically in the past decade, rates remain suboptimal amo ng low-income, inner-city youth. Timely initiation of immunization is an im portant predictor of immunization status later in childhood; however, prosp ective studies identifying predictors of initiation are lacking. Objectives. The objectives of this study were to: 1) describe immunization patterns in a cohort of infants born to predominantly low-income, inner-cit y mothers; 2) identify determinants, as measured at birth, of immunization status at 3 and 7 months of age; and 3) identify determinants of continuati on of immunization among those who initiate immunization by 3 months of age . Design. Prospective, birth cohort study. Methods. Maternal/infant dyads were systematically selected from 3 District of Columbia hospitals between August 1995 and September 1996. Three hundre d sixty-nine mothers were interviewed shortly after delivery, at 3 to 7 mon ths postpartum, and at 7 to 12 months postpartum. Medical records were revi ewed at all reported sites of care for 324 (88%) infants. Vaccinations asse ssed included diphtheria, tetanus, and pertussis; polio; and Haemophilus in fluenzae type B. Multivariate logistic regression analyses were used to det ermine factors associated with immunization status of infants at 3 and 7 mo nths of age. Results. At 3 months of age, 75% of infants were up-to-date (UTD) versus on ly 41% at 7 months. In adjusted analyses, baseline factors associated with being UTD at 3 months included enrollment in the Special Supplemental Nutri tion Program for Women, Infants, and Children (WIC) during pregnancy, inten tion to breastfeed, and presence of the infant's grandmother in the househo ld. Infants were less likely to be UTD if their mothers perceived higher ba rriers to immunization. Baseline factors associated with being UTD at 7 mon ths included lower birth order and maternal employment. Among the subset of infants who were UTD at 3 months, only 53% remained UTD at 7 months. Facto rs measured at the first follow-up interview that were associated with cont inuation of immunization at 7 months included maternal employment and lower perceived barriers. Conclusions. Immunization rates during the first 7 months of life were low in this inner-city population. Factors associated with immunization status that are potentially amenable to change included perceived barriers to immu nization and enrollment in WIC during pregnancy.