The impact of inactive infants on clinic-based immunization rates

Clinic-based immunization rates are used to evaluate clinic performance and immunization interventions, but they typically exclude so-called inactive patients (ie, those who no longer receive care at the clinic). We assessed the effect of enhanced ascertainment of inactive patients on clinic-based immunization rates and on the conclusions of a randomized controlled trial.

The study was a post hoc analysis of a cluster-randomized controlled trial. Infant randomization to the immunization intervention (4 clinics) or control group (4 clinics) was based on the site of their 2-week well-child care visit. The study was conducted at an integrated inner-city health care system serving a low-income population. A total of 2190 infants born between July 1, 1998, and June 30, 1999, who attended at least 1 postnatal visit, participated. In control sites, clinic staff documented inactive infants in the immunization registry and medical charts. The research staff undertook additional patient tracking efforts in the intervention clinics.

Control clinics identified 155 (13.4%) of 1160 children as inactive within 1 year of birth, whereas 284 (27.6%) of 1030 intervention infants were documented as inactive (P < .001). In bivariate analyses from the randomized trial, immunization rates differed between intervention and control branches. In multivariate models, immunization rates were significantly higher in the intervention branch when inactive infants were removed (adjusted relative risk 1.58; 95% confidence interval, 1.28-1.89), but not when they were included (adjusted relative risk 1.09; 95% confidence interval, 0.97-1.21).

Additional patient tracking efforts can dramatically influence inactive patient documentation and clinic-based immunization rates used for various purposes.