Predictors of age-appropriate receipt of DTaP Dose 4

In the United States, the national childhood immunization schedule calls for children to receive four doses of DTaP (diphtheria and tetanus toxoids and acellular pertussis) vaccine administered at 2, 4, 6, and 15 to 18 months. Dose 4 of DTaP is among the most frequently missed vaccines for children who are not adequately immunized. Using the 2001 National Immunization Survey, the effect of the timeliness of the first three DTaP doses was assessed on completion of the four-dose series by age 24 months and on time by age 12 to 18 months. Missing Dose 4 was more prevalent among children who received Dose 3 late (but