A PLACEBO-CONTROLLED TRIAL OF A PERTUSSIS-TOXOID VACCINE

Background. Although many whole-cell vaccines have been effective in p reventing pertussis, these vaccines are difficult to standardize and c an produce side effects. In Sweden, pertussis became endemic during th e 1970s despite vaccination. Because of its limited efficacy, the Swed ish-made whole-cell vaccine was withdrawn in 1979. Methods. To evaluat e the efficacy of an acellular vaccine consisting of pertussis toxin i nactivated by hydrogen peroxide (pertussis toroid), we conducted a ran domized, double-blind, placebo-controlled trial in Sweden. Infants wer e vaccinated with either diphtheria and tetanus toxoids atone (DT toxo ids, 1726 infants) or diphtheria, tetanus, and pertussis toxoids (DTP toxoids, 1724 infants) at 3, 5, and 12 months of age. Results. There w ere no serious reactions. With the pertussis vaccine there were slight ly more local reactions than with the DT toxoids alone, but the rates of postvaccination fever were the same. The main period of surveillanc e, which began 30 days after the third vaccination, continued for a me dian of 17.5 months. There were 312 cases of pertussis (72 in the DTP- toxoids group and 240 in the DT-toxoids group) that met the clinical c riterion (paroxysmal cough lasting greater than or equal to 21 days) a nd laboratory criteria for pertussis as defined by the World Health Or ganization. The efficacy of this acellular vaccine was 71 percent (95 percent confidence interval, 63 to 78 percent). The recipients of DTP toxoids who had pertussis had cough of shorter duration than the recip ients of DT toxoids, and fewer had whooping and vomiting. The vaccine efficacy after two doses was 55 percent (95 percent confidence interva l, 12 to 78 percent), on the basis of 14 cases in the DTP-toxoids grou p and 31 in the DT-toxoids group that met the definition of the World Health Organization. Conclusions. A pharmacologically inert, acellular pertussis-toxoid vaccine that is easily standardized is safe and conf ers substantial protection against pertussis.