DTaP Is Not Associated with Seizures

Summary and Comment |
August 25, 2010

DTaP Is Not Associated with Seizures

  1. Cornelius W. Van Niel, MD

This large postlicensure study shows convincingly that no association exists between DTaP and seizure.

  1. Cornelius W. Van Niel, MD

Diphtheria, tetanus, whole-cell pertussis vaccine (DTP) is associated with increased risk for seizure during the immediate postvaccination period. In 1997, diphtheria-tetanus-acellular pertussis vaccine (DTaP) was licensed and recommended for routine vaccination in children. Postlicensure studies showed fewer seizures after vaccination with DTaP than with DTP. But is risk for seizure after DTaP zero? To find out, researchers examined data for more than 400,000 children (age range, 6 weeks to 23 months) who were enrolled in managed care organizations that participated in the Vaccine Safety Datalink Project from 1997 to 2006. Seizure was defined by inpatient and emergency department diagnostic codes (including febrile and nonfebrile seizures).

Two analyses were performed. In a risk-interval cohort analysis, the seizure rate during the 3 days after DTaP vaccination was compared with the background seizure rate for all children during all other time periods outside the 3-day window. In a self-controlled case series analysis, children who had seizures during the 3-day window served as their own controls during the time outside the window. After adjustment for year, season, age, sex, and concurrent measles-mumps-rubella vaccination, no statistically significant association was found between DTaP vaccination and risk for seizure within 3 days in either analysis (relative risks, 0.87 for the cohort analysis and 0.91 for the cases series analysis).

Comment

This is the largest postlicensure study of DTaP and seizure, and it shows convincingly that no association between the two exists. The seizure rate was highest during the 3 days after the fourth dose of DTaP, but the background seizure rate also peaked around the age at which the dose is administered, and the association disappeared after adjustment for age. The strength of the cohort analysis is its calculation of the background seizure rate. The strength of the case series is that it can avoid a false-negative association caused by children with seizures who do not receive DTaP vaccines. How this study prompts changes in the recommended contraindications to and precautions for the DTaP vaccine will be interesting to see.

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