Background. The goal of the trial was to determine the efficacy of a multicomponent acellular pertussis vaccine against Bordetella illnesses in comparison with a whole-cell product and DT.
Design. In a randomized, double-blind fashion, 2- to 4-month-old infants received 4 doses of either DTP or DTaP vaccine at 3, 4.5, 6, and 15 to 18 months of age. The controls received 3 doses (3, 4.5, 15 to 18 months of age) of DT vaccine. The DTP vaccine was Lederle adsorbed vaccine (licensed in the United States) and DTaP was Lederle/Takeda adsorbed vaccine. Follow-up for vaccine efficacy started 2 weeks after the third dose (DTP/DTaP) and at the same age (6.5 months) in DT recipients. Reactogenicity of all doses of all three vaccines was documented by standardized parent diary cards. In addition, all subjects were monitored for respiratory illnesses and serious adverse events by biweekly phone calls.
Results. From May 1991 to January 1993, a total of 10 271 infants were enrolled: 8532 received either DTP or DTaP and 1739 received DT. Specific efficacy against B pertussisinfections with cough ≥7 days duration was 83% (95% confidence interval [CI]: 76–88) and 72% (95% CI: 62–79) for DTP and DTaP, respectively; results for DTP and DTaP based on ≥21 days of cough with either paroxysms, whoop or posttussive vomiting (PWV) were 93% (95% CI: 89–96) and 83% (95% CI: 76–88), respectively. For DTaP vaccine, efficacy was higher after the fourth dose as compared with its efficacy after the third dose (78% vs 62% for cough ≥7 days and 85% vs 76% for cough ≥21 days with PWV). For DTP vaccine, efficacy was less varied after the third and fourth dose (78% vs 85% for cough ≥7 days and 93% vs 93% for cough ≥21 days with PWV). In contrast with DTP, the DTaP vaccine had some efficacy against B parapertussisinfection (point estimate for cough ≥7 days: 31% [95% CI: −10–56]). All vaccines were generally well-tolerated. However, side reactions were significantly less after DTaP compared with DTP.
Conclusions. Like other multicomponent acellular pertussis vaccines, the Lederle/Takeda DTaP vaccine demonstrated good efficacy against mild and typical pertussis due to B pertussisinfections. Interestingly, it also may have some efficacy againstB parapertussis. Based on the results of this trial, the vaccine was licensed in the United States in December 1996 for all 5 doses of the currently recommended immunization schedule in this country.