Large outbreak of pertussis among young children in Chicago, 1993: investigation of potential contributing factors and estimation of vaccine effectiveness

Pediatr Infect Dis J. 1996 Aug;15(8):655-61. doi: 10.1097/00006454-199608000-00004.


Background: An outbreak of pertussis from July, 1993, to April, 1994, in Chicago was investigated to identify potential contributing factors.

Methods: Surveillance was enhanced to identify cases. Information from a vaccination coverage survey was used to define a retrospective cohort to estimate vaccine effectiveness of three or more doses of pertussis vaccine.

Results: The median age of 218 reported cases was 8 months, 46% had Hispanic surnames and cases were clustered geographically. Vaccination status was known for 173 of 191 (91%) children younger than 6 years of age. Of these 173, 90 (52%) were younger than 7 months, and 35 (20%) children at least 7 months of age had received fewer than 3 doses of pertussis vaccine. Pertussis vaccine effectiveness was 76% (95% confidence interval, 29 to 92).

Conclusions: The limited ability of the current pertussis vaccination schedule to protect young infants accounted for 52% of cases, primary vaccine failure accounted for 28% of cases and failure to vaccinate children on time accounted for 20% of cases in young children. Low vaccine effectiveness did not appear to be a contributing factor.

MeSH terms

  • Causality
  • Chicago / epidemiology
  • Child, Preschool
  • Diphtheria-Tetanus-Pertussis Vaccine / administration & dosage*
  • Diphtheria-Tetanus-Pertussis Vaccine / immunology
  • Disease Outbreaks*
  • Humans
  • Infant
  • Pertussis Vaccine / administration & dosage
  • Pertussis Vaccine / immunology
  • Vaccination / statistics & numerical data*
  • Whooping Cough / epidemiology*
  • Whooping Cough / prevention & control


  • Diphtheria-Tetanus-Pertussis Vaccine
  • Pertussis Vaccine