[Immunogenicity and safety of a tetanus-diphtheria vaccine (adult type): clinical trial in adults].
BACKGROUND: The administration of tetanus-diphtheria vaccine (Td, "adult" type) as booster dose every ten years, instead of tetanus toxoid, is a usual practice in the U.S., and its is being envisaged by the Spanish health authorities. In the present trial, the immunogenic capacity and the safety profile of the administration of one dose of Td vaccine to healthy adults, previously immunized to tetanus and diphtheria, was evaluated. METHODS: Healthy adults, who received one i.m. (deltoid) dose of Td vaccine containing 1.5 Lf and 10 Lf of adsorbed diphtheria and tetanus toxoids, respectively, participated in the study. Just before vaccination (baseline), and 4 weeks later, tetanus and diphtheria antibodies titres were determined by Elisa. The cut-off of these tests is 0.1 IU/ml. In this study, antitoxin titres > or = 0.1 IU/ml were considered as protective. Titres < 0.1 IU/ml were arbitrarily given the value of 0.05 IU/ml. Participating subjects recorded during the 3 days post-vaccination any local and systemic adverse events. RESULTS: One hundred and thirty nine medical students and health care workers (age +/- SD: 26 +/- 6 years) participated in this trial. At baseline and 4 weeks, the seroprotective levels were 70% and 100% for tetanus, and 31% and 90% for diphtheria, respectively. The geometric mean titres for tetanus and diphtheria antibodies at baseline and 4 weeks were: 0.59 and 8.54 IU/ml and 0.09 and 1.63 IU/ml, respectively. 82% of the subjects recorded some kind of adverse events, most of them local and mild. 66% referred local pain 24 h after the administration of the vaccine. Only 12% reported any kind of systemic adverse event: malaise (5%) and headache (4%) were the most commonly reported. All the adverse events were transient and did not require any medical attention or therapy. CONCLUSIONS: The Td vaccine tested in this study, when administered as booster dose to previously immunized adults, is highly immunogenic and shows an acceptable safety profile.