Acellular pertussis vaccines: the rationale for an efficacy trial in Germany.

After concern about the safety of diphtheria-tetanus toxoid-whole cell pertussis vaccines (DTPw), the recommendation to vaccinate children with DTPw was withdrawn in 1974 in the former West Germany. This led pertussis cases to increase to an estimated 100,000 annually. Despite renewal of the vaccination recommendation in 1991, vaccine use remained low. The German health care structure assures regular contact between most children and pediatricians. This enabled the conduct of a large efficacy trial with a diphtheria-tetanus toxoid-acellular pertussis (DTPa) vaccine. Because a placebo-controlled trial was not ethically possible, a prospective household contact study with a blinded clinical follow-up was done. Possible study participants were screened by their pediatrician, who also initiated diagnostic procedures. Clinical follow-up was done by another locally based but independent and blinded physician. Vaccine efficacy was calculated to be 89% (95% confidence interval, 76.6%-94.6%). None of the identified confounding factors biased results in favor of the DTPa vaccine.