Learning Objectives for this Presentation:
By the end of this presentation participants will be able to understand how administration of the 4th DTaP prior to 15 months has a significant impact on immunization rates at 24 months of age.

Background:
Data indicate that the completion of the DTaP series, especially the 4th dose, lags behind the completion of other childhood immunizations in the 4:3:1:3:3 series, both in Oregon and nationally. Knowing more about the reasons for these lower rates of completion for the DTaP series is important in creating effective strategies for improving overall up-to-date rates among two-year olds.

Objectives:
To quantify how the timing of the administration of the fourth dose of DTaP affects overall 4:3:1:3:3 series coverage rates at 24 months of age.

Methods:
The data in this study were obtained from assessments of private clinics done by the Oregon Immunization Program's routine AFIX process. Data were exported from CASA into Excel where patient-level data were merged and deduplicated. The resulting 23,719 individual patients and their immunization histories were then imported into SPSS for analysis. Time to immunization and up-to-date status at 24 months of age were assessed using Pearson Chi-square test.

Results:
Of patients who received their 4th DTaP those who did so before the end of their 14th month (426 days of age) were statistically significantly more likely to have their full 4:3:1:3:3 compliment of immunizations by 24 months of age than those who received their shot after 14 months of age.

Conclusions:
The preliminary results of this study highlight the importance of giving the fourth dose of DTaP as early as possible, and suggest that a practice of administering the 4th dose of DTaP earlier than 15-18 months can improve the 4:3:1:3:3 series rate for two-year olds.