Improving immunization rates at 18 months of age: implications for individual practices

We sought to model the effect that a targeted immunization visit at 18 months of age could have on immunization rates of preschool-aged children in a sample of pediatric practices.

We conducted retrospective chart reviews in six practices of all active patients aged 18-30 months. Up-to-date (UTD) status was defined as receipt of four diphtheria-tetanus-acellular pertussis, three polio, one measles-mumps-rubella, three hepatitis B, and one varicella vaccines. Haemophilus influenza tybe b vaccine was not included due to a shortage in vaccine supply during the time of the study. Practice vaccination rates were determined at 17 months, 18 months, and the age at assessment. Of those not UTD at 17 months, the percentage of children who could be brought UTD with one visit was calculated for each practice. This calculated rate was compared with the measured rate at 18 months of age and at the age of assessment.

At each practice, we reviewed 183-616 charts (median = 382). Observed UTD immunization rates at 17 months ranged from 26% to 64% (median = 38%) and increased 3 to 27 percentage points (median = 6) from age 17 months to 18 months and 9 to 39 percentage points (median = 17) from age 17 months to the age at assessment. A simulated vaccination visit at 18 months of age could improve the UTD rates from 27 to 61 percentage points (median = 44).

Practice-based interventions aimed at encouraging an 18-month well-child visit that emphasizes delivery of vaccines have the potential to substantially increase timely vaccination rates among individual practices.