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Prevalence and predictors of immunization among inner-city infants: a birth cohort study
R A Brenner1, B G Simons-Morton, B Bhaskar
1National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA. brennerr@nih.gov
Insights
Immunization rates for infants in low-income, inner-city areas remain low, with only 41% up-to-date by 7 months. Perceived barriers and WIC enrollment are key factors influencing childhood immunization status.
Area of Science:
- Pediatrics
- Public Health
- Epidemiology
Background:
- Childhood immunization rates have improved but remain suboptimal in low-income, inner-city populations.
- Timely immunization initiation is a critical predictor of later childhood immunization status.
- Prospective studies on predictors of immunization initiation are lacking.
Purpose of the Study:
- To describe immunization patterns in a cohort of predominantly low-income, inner-city infants.
- To identify birth-measured determinants of infant immunization status at 3 and 7 months.
- To identify determinants of immunization continuation by 7 months among those initiating by 3 months.
Main Methods:
- Prospective birth cohort study involving 369 mothers and 324 infants in Washington D.C. (1995-1996).
- Data collected via maternal interviews and medical record reviews.
- Multivariate logistic regression analyzed factors associated with immunization status at 3 and 7 months.
Main Results:
- Only 41% of infants were up-to-date (UTD) on immunizations by 7 months.
- At 3 months, UTD status was associated with WIC enrollment, intention to breastfeed, and grandmother's presence; higher perceived barriers were associated with lower UTD rates.
- At 7 months, UTD status was linked to lower birth order and maternal employment; only 53% of infants UTD at 3 months remained UTD at 7 months.
Conclusions:
- Low immunization rates were observed in this inner-city population during the first 7 months of life.
- Potentially modifiable factors influencing immunization status include perceived barriers and WIC enrollment during pregnancy.
Context:
Although the proportion of US children who are appropriately immunized increased dramatically in the past decade, rates remain suboptimal among low-income, inner-city youth. Timely initiation of immunization is an important predictor of immunization status later in childhood; however, prospective 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-city mothers; 2) identify determinants, as measured at birth, of immunization status at 3 and 7 months of age; and 3) identify determinants of continuation 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 hundred sixty-nine mothers were interviewed shortly after delivery, at 3 to 7 months postpartum, and at 7 to 12 months postpartum. Medical records were reviewed at all reported sites of care for 324 (88%) infants. Vaccinations assessed included diphtheria, tetanus, and pertussis; polio; and Haemophilus influenzae type B. Multivariate logistic regression analyses were used to determine factors associated with immunization status of infants at 3 and 7 months of age.
Results:
At 3 months of age, 75% of infants were up-to-date (UTD) versus only 41% at 7 months. In adjusted analyses, baseline factors associated with being UTD at 3 months included enrollment in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) during pregnancy, intention to breastfeed, and presence of the infant's grandmother in the household. Infants were less likely to be UTD if their mothers perceived higher barriers to immunization. Baseline factors associated with being UTD at 7 months 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. Factors measured at the first follow-up interview that were associated with continuation 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 immunization and enrollment in WIC during pregnancy.