Bibliographical noteFunding Information:
All of the acellular pertussis vaccines currently licensed in the United States have been evaluated for efficacy in clinical trials, but it can be extremely difficult to draw comparisons across the various trials. For facilitation of comparison across studies, most efficacy trials use the World Health Organization (WHO) definition of pertussis, which is 21 days of paroxysmal cough, plus laboratory confirmation that the illness is due to pertussis. 89 Even this apparently rigorous definition may be difficult to compare across trials, because of differences in choice and sensitivity of confirmatory assays. In spite of these limitations, some insights into the relative efficacy of acellular vaccines have been gleaned. Of particular importance are the efficacy studies of acellular pertussis vaccines sponsored by the National Institutes of Allergy and Infectious Diseases (NIAID) in Italy and Sweden. 9°,91 These studies were randomized, double-blinded, rigorously controlled trials. Infants were immunized at 2, 4, and 6 months of age, and each study contained both a placebo group and a whole-cell control group. The Italian study compared 2 different 3-component vaccines (containing PT, FHA, and PRN) with whole-cell vaccine, and found an 84% efficacy for both 3-component vaccines, but only a 36% efficacy for whole-cell vaccine. The Swedish study revealed an efficacy for a 5-component acellular pertussis vaccine of 85.2%, compared with efficacy for a 2-component vaccine of 58.9% and for a whole-cell vaccine of 48.3%.
We acknowledge the assistance of Toni Cunningham in preparation of the manuscript. The Division of Infectious Diseases at Children's Hospital, Cincinnati, Ohio, is supported as a Vaccine Treatment and Evaluation Unit (VTEU) site through the National Institutes of Health (NIH AI-45252).