Learning Objectives for this Presentation:
By the end of the presentation participants will be able to:
- Discuss effects of recommending minimum interval vaccination schedules.
- Discuss strengths and limitations of registry data.

Background:
Arizona experienced a statewide pertussis outbreak from May 2005 through October 2005. In response to this outbreak, state and local health officials recommended use of the minimum intervals for DTaP vaccination. Concerns were raised during this time that this recommendation might disrupt vaccination schedules.

Objectives:
We evaluated the effects of this recommendation on the three-dose DTaP completion rates and on age at third DTaP dose.

Methods:
Immunization records for children born between February and September 2005 and who received their first valid dose of DTaP during the statewide outbreak were pulled from Arizona's immunization registry. Children who received a second or third recorded dose after one year of age were excluded. Children who were included (N = 44,074) were categorized based on the number of valid DTaP doses they received on the minimum interval schedule.

Results:
A significantly higher percentage of children with at least one dose of DTaP on the minimum interval schedule received three doses prior to one year of age (87%) compared to children who were not vaccinated using the minimum interval schedule (68%, p-value < 0.001). The mean age at the third dose was lower among children with at least one dose on the minimum interval schedule (24.1 weeks) compared to children who were not vaccinated using the minimum interval schedule (29.9 weeks).

Conclusions:
Children receiving at least one dose of DTaP on the minimum interval schedule were more likely to receive a third dose of DTaP before one year of age, and to receive their third dose earlier, when compared to children who were not vaccinated using the minimum interval schedule.