Timing of DTaP Doses and Predictors for Missing the Fourth Dose, National Immunization Survey, 2007

Background:
Vaccination coverage of 4+ doses of DTaP has not reached 90%, but coverage of 3+DTaP has exceeded 90%. The fourth dose of DTaP is often missed.

Objectives:
To estimate the cumulative proportion receiving the 1st – 4th doses of DTaP among children aged 19-35 months, compare the cumulative proportions, and determine the significant predictors for not receiving the 4th DTaP dose.

Methods:
Kaplan-Meier estimation method was used to estimate the cumulative proportion receiving the 1st – 4th dose of DTaP through 35 months of age. The multivariable logistic regression method was adopted to find significant predictors for missing DTaP dose 4 for children aged 19-35 months. Data analyses were performed with SUDAAN Kapmeier and Multilog procedures.

Results:
By 24 months of age, the estimated cumulative proportion receiving the 1st dose of DTaP was 98%, the 2nd dose was 97%, the 3rd dose was 95%, and the 4th dose was 84%.
Missing dose 4 was more prevalent among children who received dose 1, dose 2, or dose 3 late than among children who received dose 1, dose 2, or dose 3 on time (38% vs. 10%; 27% vs. 8%; 20% vs. 6%; all P-value < 0.01). Receipt of dose 1 and/or dose 3 late, having more than one provider, and being a younger mother were the significant predictors for missing the 4th dose of DTaP (P-value < 0.01).

Conclusions:
Measures such as targeted parent remind/recall efforts to parents of children with late doses of DTaP, encouraging parents to follow or accelerate the vaccination schedule, and using every office visit by the ‘late' children as an opportunity to vaccinate may help to ensure at-risk children receive their 4th dose of DTaP.