Similarities Between the Pathogenesis of and Immunity to Diphtheria and Pertussis: The Complex Nature of Serum Antitoxin‐Induced Immunity to These Two Diseases

Despite data from animal studies, seroepidemiological surveys, and controlled clinical trials, skepticism persists about immunity to pertussis conferred by serum IgG neutralizing antibodies (antitoxin). This is largely prompted by the absence of a "protective" level of antitoxin. Examination of the similarities between the pathogenesis and immunity to pertussis and diphtheria provides an explanation for this dilemma. As with pertussis, diphtheria toxoid vaccination confers only approximately 70% immunity on an individual basis, individuals with protective levels of antitoxin may contract diphtheria, and about 50% of the entire population, especially adults, have less than protective levels of antitoxin. The virtual disappearance of diphtheria followed vaccination of the entire population with diphtheria toxoid, which blocked transmission of toxigenic Corynebacterium diphtheriae and thus reduced the pathogen to almost undetectable levels. The individual and community-based immunity induced by diphtheria toxoid, we hypothesize, is similar to that of pertussis and pertussis toxoid.