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.
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.
Department of Pediatrics, University of Ottawa, Ottawa, Ontario, Canada. lesaux@cheo.on.ca
Nicole
N
Le Saux
Nicholas J
NJ
Barrowman
Dorothy L
DL
Moore
Sharon
S
Whiting
David
D
Scheifele
Scott
S
Halperin
D016907:Adverse Drug Reaction Reporting Systems / Q000706:statistics & numerical data; D002170:Canada; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000009:adverse effects; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines / Q000008:administration & dosage / Q000009:adverse effects*; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D005260:Female; D018073:Haemophilus Vaccines / Q000008:administration & dosage / Q000009:adverse effects; D006760:Hospitalization / Q000639:trends*; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D022542:Measles-Mumps-Rubella Vaccine / Q000009:adverse effects; D009123:Muscle Hypotonia / Q000453:epidemiology* / Q000209:etiology; D011054:Poliovirus Vaccine, Inactivated / Q000008:administration & dosage / Q000009:adverse effects; D012449:Safety; D003294:Seizures, Febrile / Q000453:epidemiology* / Q000209:etiology; D022282:Vaccines, Acellular / Q000009:adverse effects
D015721:Diphtheria-Tetanus-Pertussis Vaccine; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines; D018073:Haemophilus Vaccines; D022542:Measles-Mumps-Rubella Vaccine; D011054:Poliovirus Vaccine, Inactivated; D022282:Vaccines, Acellular