In a randomized, double-blind fashion, 8532 infants (2-4 mo. old) received 4 doses of either DTP or DTaP; 1739 infants (controls) received DT vaccine. All subjects were monitored for illnesses by biweekly phone calls. Cough illnesses ≥ 7d duration were studied (culture + serology). All cough illnesses ≥ 14d duration were also evaluated by 1 of 3 central investigators (SS, MÜ, UH). Efficacy for DTaP and DTP against lab confirmed B. pertussis (Bp) infection increased with severity of illness: 72% (95% CI:62-79) and 83% (76-88) for cough ≥ 7d and 83% and 93% (cough ≥ 21d + paroxysms, whoop or posttussive vomiting), respectively. Efficacy rates based on central investigators' clinical dx of probable or definite pertussis were 82% (DTaP) and 85% (DTP). Illness due to B. parapertussis (Bpp) infection was frequent with a rate 0.9 per 100 person years in DT recipients. Although Bpp has two similar antigens (FHA and pertactin) as Bp which are contained in both DTP and DTaP, neither vaccine was efficacious [VE DTaP = 31% (95% CI: -10-56); DTP = -6% (95% CI: -64-31]. In conclusion, both DTP and DTaP protected against mild and severe Bp infections. The lack of efficacy against illness due to Bpp raises the possibility of considering Bpp antigens as well as Bp antigens in future pertussis vaccines.

This study was supported by Wyeth-Lederle Vaccines and Pediatrics.