A RANDOMIZED DOUBLE-BLIND TRIAL COMPARING A 2-COMPONENT ACELLULAR TO A WHOLE-CELL PERTUSSIS-VACCINE IN SENEGAL

A randomized, double-blind trial comparing a diphtheria-tetanus-acellu lar pertussis vaccine (DTaP) (pertussis toxoid and filamentous hemaggl utinin) with a whole-cell vaccine (DTwF) was conducted. A case-contact study was nested in the trial to estimate absolute efficacy. From 199 0 through 1994, 4181 children were randomized to receive one of the va ccines at 2, 4, and 6 months. Severe adverse events were monitored wee kly during two visits after vaccination. Fewer serious adverse events were observed after DTaP. Surveillance for cough illnesses persisting more than 7 days, in children under 15 years of age, was made by weekl y home visits. Examining physicians, blind to vaccination status, took samples for culture and serologic testing. Pertussis was defined as 2 1 or more days of cough confirmed by culture, serology, or contact wit h a culture-confirmed person. Beginning 28 days after the third vaccin e dose, the overall ratio of pertussis incidence in the DTaP group rel ative to the DTwP group (RRac/wc) was 1.54 (95% CI, 1.23-1.93). In chi ldren younger than 18 months of age, RRac/wc was 1.16 (95% CI, 0.77-1. 73) and 1.76 (95% CI, 1.33-2.33) in children older than 18 months, whi ch suggests a shorter duration of protection with the acellular vaccin e (P = 0.090). Absolute efficacy estimates derived from the case-conta ct study confirmed the lower protection afforded by the acellular vacc ine compared with the whole-cell vaccine: 31% (95% CI, 7-49) versus 55 % against the protocol case definition, and 85% (95% CI, 66-93) versus 96% for the more severe WHO case definition. Although vaccination wit h DTaP provided a lower degree of protection than the highly effective DTwP, this difference was less prominent before 18 months of age, the customary age for a fourth dose. The safer DTaP vaccine may prove a v aluable substitute for whole-cell vaccines when used in a schedule tha t includes a booster dose. (C) 1997 Elsevier Science Ltd.