Why do pertussis vaccines fail?

The first reason, and perhaps the most important one, is that our estimates of vaccine efficacy have been inflated because of case definition.3–11 At the time of the pediatric diphtheria and tetanus toxoids and acellular pertussis (DTaP) vaccine efficacy trials in the early 1990s, it was hoped that a universal case definition could be developed so that the results of the various trials could be compared. To this end, the World Health Organization (WHO) case definition was developed.3 The primary case definition required laboratory confirmation and$21 days of paroxysmal cough. I was a member of the WHO committee and disagreed with the primary case definition because it was clear at that time that this definition would eliminate a substantial number of cases and therefore inflate reported efficacy values.4–11 Nevertheless, the Center for Biologics Evaluation and Research of the Food and Drug Administration accepted this definition, and package inserts of the US-licensed DTaP vaccines reflect this. For example, Infanrix (containing 25mg pertussis toxin [PT], 25mg filamentous hemagglutinin [FHA], and 8 mg pertactin [PRN]) and Daptacel (containing 10 mg PT, 5 mg FHA, 5 mg fimbriae [FIM]-2/3, and 3 mg PRN) have stated efficacies of 84% and 85% respectively. When less severe cough illness is included, however, the efficacies of these 2 vaccines decrease to 71% and 78% respectively.10,11