Diphtheria booster vaccination: one or two injections?

In a prospective, controlled, randomized, multicenter study the immunogenic ity and tolerance of a single vaccination (day 0) and two (day 0, 28) boost er vaccinations against diphtheria were compared in subjects who had receiv ed their last diphtheria vaccination more than 10 years ago. 415 subjects r eceived the first booster vaccination, and 203 were vaccinated twice. The g eometric mean diphtheria antitoxin concentration after the first booster (d ay 28) was 2.354 I.U./ml, and after the second booster (day 56) 2.238 I.U./ ml. Prior to the first vaccination 48.9% of the subjects had a diphtheria a ntitoxin level below 0.1 I.U./m; after the first and second boosters 95.4% and 97.5% of subjects, respectively, showed a level of at least 0.1 I.U./ml . A clear serological effect of a second booster 4 weeks after the first on e could not be demonstrated. (C) 1999 Elsevier Science Ltd. All rights rese rved.