Decrease in hospital admissions for febrile seizures and reports of hypotonic-hyporesponsive episodes presenting to hospital emergency departments since switching to acellular pertussis vaccine in Canada: a report from IMPACT

Pediatrics. 2003 Nov;112(5):e348. doi: 10.1542/peds.112.5.e348.


Objective: Acellular pertussis vaccines were introduced with the promise of an improved safety profile compared with whole-cell vaccines. In 1997-1998, Canada adopted 1 combination acellular pertussis vaccine, having previously used 1 particular combination whole-cell pertussis vaccine. We hypothesized that the change would result in a decrease in hospitalization rates for seizures and reports of hypotonic-hyporesponsive episodes (HHEs) temporally related to pertussis vaccination.

Methods: Active surveillance was performed between 1995 and 2001 by the Immunization Monitoring Program-Active monitors at 12 hospitals using standard case definitions. Seizures had to occur within 72 hours after immunization with a pertussis-containing vaccine or 5 to 30 days after immunization with measles-mumps-rubella vaccine. HHE episodes had to occur within 48 hours of receipt of a pertussis-containing vaccine. Poisson regression models were used to compare the average number of monthly admissions for seizures and HHEs before and after introduction of the acellular pertussis vaccine.

Results: We found a 79% decrease in febrile seizures associated with receipt of pertussis vaccine but no significant decrease in febrile seizures temporally related to measles-mumps-rubella between 1995-1996 and 1998-2001. There was a 60% to 67% reduction in HHEs associated with pertussis-containing vaccines between the same time periods, depending on case definition.

Conclusions: The risks of febrile seizures and HHEs after pertussis-containing vaccine declined significantly with the introduction of acellular pertussis vaccine in Canada. Active surveillance systems are important for detecting trends in uncommon adverse events after routine immunizations.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adverse Drug Reaction Reporting Systems / statistics & numerical data
  • Canada
  • Child
  • Child, Preschool
  • Comorbidity
  • Diphtheria-Tetanus-Pertussis Vaccine / adverse effects
  • Diphtheria-Tetanus-acellular Pertussis Vaccines / administration & dosage
  • Diphtheria-Tetanus-acellular Pertussis Vaccines / adverse effects*
  • Emergency Service, Hospital / statistics & numerical data*
  • Female
  • Haemophilus Vaccines / administration & dosage
  • Haemophilus Vaccines / adverse effects
  • Hospitalization / trends*
  • Humans
  • Incidence
  • Infant
  • Male
  • Measles-Mumps-Rubella Vaccine / adverse effects
  • Muscle Hypotonia / epidemiology*
  • Muscle Hypotonia / etiology
  • Poliovirus Vaccine, Inactivated / administration & dosage
  • Poliovirus Vaccine, Inactivated / adverse effects
  • Safety
  • Seizures, Febrile / epidemiology*
  • Seizures, Febrile / etiology
  • Vaccines, Acellular / adverse effects


  • Diphtheria-Tetanus-Pertussis Vaccine
  • Diphtheria-Tetanus-acellular Pertussis Vaccines
  • Haemophilus Vaccines
  • Measles-Mumps-Rubella Vaccine
  • Poliovirus Vaccine, Inactivated
  • Vaccines, Acellular