Development of a vaccine tracking system to improve the rate of age-appropriate primary immunization in children of lower socioeconomic status.

We conducted a randomized, controlled trial to determine the effectiveness of an immunization tracking system designed to increase the number of infants of lower socioeconomic status who receive their primary series of vaccinations at age-appropriate times. By 7 months of age, 91% (274/301) of the infants in the intervention group were up-to-date on their primary series of vaccinations versus 72% (214/296) of the infants in the control group (p < 0.0001). The estimated cost of follow-up for each infant in the intervention group was $18.05.