Effects of a minimum interval immunization schedule for diphtheria and tetanus toxoids and acellular pertussis vaccination during a pertussis outbreak.

OBJECTIVE: To examine the impact of a minimum interval schedule for administering diphtheria and tetanus toxoids and acellular pertussis vaccine (DTaP) in infants during a statewide pertussis outbreak on receipt of inactivated polio vaccine (IPV) and pneumococcal conjugate vaccine (PCV).

DESIGN: Retrospective cohort study using the state immunization registry.

SETTING: Arizona.

PARTICIPANTS: Arizona children born between February 1 and September 30, 2005, who received their initial DTaP dose during a statewide pertussis outbreak (N = 45 129). Main Exposures Children who received at least 1 dose of DTaP on the minimum interval schedule (minimum interval group) compared with children who received all doses of DTaP on the standard childhood and adolescent immunization schedule (standard group).

OUTCOME MEASURES: Timing and receipt of 3 doses of the DTaP, IPV, and PCV.

RESULTS: Compared with children in the standard group, children in the minimum interval group were more likely to receive 3 doses of DTaP (relative risk, 1.34; 95% confidence interval, 1.32-1.35), 3 doses of IPV (1.27; 1.25-1.29), and 3 doses of PCV (1.37; 1.35-1.39).

CONCLUSION: Recommending a minimum interval DTaP schedule during a statewide pertussis outbreak had a positive association with the receipt of IPV and PCV, 2 vaccines normally administered at the same time as DTaP.