Overdose of booster tetanus toxoid given in error: a clinical study

16 reserve soldiers received an overdose of tetanus toxoid vaccine (5 ml instead of 0.5 ml) in error. We assessed the incidence and severity of adverse reactions and determined tetanus antibody titer immediately and after 5 days, 1 month and 1 year, and compared it with the titers in a control group of 20 soldiers. The incidence and severity of reactions was significantly higher in the overdose group. The mean tetanus antibody titer rose to similar levels in both groups after 1 month (153.75 +/- 82.5 IU/ml and 62.02 +/- 42.15 IU/ml respectively) but decreased sharply after 1 year in the overdose group.