Counting the Shots: A Model for Immunization Screening and Referral in Nonmedical Settings

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Abstract
Background. Clinics of the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) have become important partners in efforts to improve vaccination coverage in low income children. However, the time required to assess all antigens in each child’s vaccination record may exceed the capacity of many of these clinics. Seeking a solution, experts recommended assessing up-to-date (UTD) status only for the diphtheria-tetanus-acellular-pertussis (DTaP) vaccine and treating this as a proxy measure for all vaccines in the childhood schedule. Whether this single vaccine screening method represents an acceptable alternative to the traditional multiple-vaccine method as a basis for improving overall immunization coverage levels in this vulnerable population has not been demonstrated. Objective. To evaluate the validity of the proposed simplified method for assessing immunization status in a nationally representative population of infants and children who had ever been enrolled in WIC before 35 months old. Methods. This was a cross-sectional analysis of the 2000 National Immunization Survey representing children ages 3 to 24 months who had ever been enrolled in WIC. For the 6277 children in the study population, we compared personal records of completion status for DTaP with personal records of completion status for all immunizations appropriate for age in the combination 4:3:1:3 schedule to see which of the 2 (single vs multiple screening) methods would better predict the child’s true (provider-reported) status for the 4:3:1:3 series. The main outcome measures were the comparative sensitivity, specificity, and overall test efficiency of the 2 methods in correctly identifying underimmunized WIC children. Results. Completion status for DTaP was less sensitive than completion status for all vaccinations in correctly identifying truly underimmunized children (sensitivity = 70% and 77%, respectively). However, it was more specific in correctly identifying children who were truly UTD for age (specificity = 86% and 82%, respectively). The 2 methods were essentially identical with respect to overall test efficiency (82% and 81% for DTaP assessment and assessment of all vaccines, respectively). Conclusions. Given limited resources to do immunization screening and referral in nonmedical settings such as WIC, simplifying the process by using DTaP from the personal vaccination record as a proxy for the 4:3:1:3 series is a viable option. Loss in sensitivity may well be offset by gains in the capacity of WIC clinics to screen more children.