Mixing of diphtheria, tetanus, and acellular pertussis (DTaP) vaccines in a population of children in managed care

The Advisory Committee on Immunization Practices recommends administering diphtheria, tetanus and acellular pertussis (DTaP) vaccines to children at 2, 4, 6, 15-18 months, and 4-6 y of age; preferably with the same-brand vaccine for the whole series. We estimated age-appropriate DTaP dose completion and the proportion of children receiving a "mixed" DTaP vaccination series (ie, including DTaP vaccines from ≥ 2 brands) across the 3 milestones. Commercially-insured children born between 01/01/2003 and 04/30/2011 were identified from United States health insurance claims data and assigned to ≥ 1 of 3 study cohorts based on the duration of continuous health plan enrollment: 1) birth to <8 months; 2) birth to <20 months; 3) birth to <7 years. Dose completion and brand mixing of the first 3, first 4 or all 5 doses were measured in the respective cohorts. Administered DTaP vaccinations were identified in claims data and classified by brand (based on vaccine components and manufacturer). The analysis included children who received ≥ 2 DTaP vaccinations and had known brand information for all doses. Age-appropriate dose completion was 77% with 3 doses (<8 months cohort), 71% with 4 doses (<20 months cohort), and 85% with 5 doses (<7 years cohort). Mixed DTaP series were received by 4.7% (95% confidence interval [CI]: 4.6%-4.7%) in the <8 months cohort, 29.0% (95% CI: 28.6%-29.4%) in the <20 months cohort, and 39.0% (95% CI: 34.5, 43.6) in the <7 years cohort. DTaP mixing was just 4.7% for the first 3 doses but subsequently increased with the number of administered doses.