Who Missed the Fourth Dose of DTaP? A Birth Year Cohort Risk Study, National Immunization Survey 2007-2009

Background: The Advisory Committee on Immunization Practices (ACIP) recommends four doses of DTaP vaccine by 2 years of age. The 4^th DTaP is often missed. However the risk factors associated with children missing the 4^th DTaP have not been fully investigated.

Objectives: To estimate risk ratio of late versus on-time vaccination for missing the 4^th DTaP by the 1^st through the 3^rd DTaP; evaluate the adjusted risk ratio for missing the 4^th DTaP between the strata of significant risk factors identified.

Methods: Data collected from the 2006 birth year cohort obtained from the 2007 through 2009 NIS datasets were analyzed. Vaccinations administered before 24 months among children at least 24 months old were examined. Weighted categorical data analyses were conducted to estimate the risk ratio. The step-wise multivariable logistic regression was applied to identify significant risk factors and evaluate adjusted risk ratios for missing the 4^th DTaP.

Results: The bivariate analysis showed that risk for missing the 4^th DTaP among children who received the 1^st, 2^nd, 3^rd DTaP late were 317%, 282%, 229% higher than children who received the 1^st, 2^nd, 3^rd DTaP on time respectively. The adjusted risks for missing the 4^th DTaP were 58%, 54%, 100% higher for children who received the 1^st, 2^nd, 3^rd DTaP late than on time respectively; 26% higher for children whose mother was ≤ 29 years old; 38% higher for children who were not first born; 43% higher for children whose family moved from a different state. All adjusted risk ratios are significantly higher than ‘1’ at level P-value < 0.05.

Conclusions: Providers should consider the use of remind-recall systems especially for children known to be at high risk of missing the 4^th DTaP, such as those children late receiving earlier dose.