The immune response to booster vaccination against diphtheria toxin at age 18-21 years

The purpose of this study was to evaluate the immunity of young Israeli adults against the diphtheria toxin and to assess the immune response to a 2 Lf booster vaccination of diphtheria. The antibody levels against the toxin were measured in 200 volunteers aged 18-21. Later, a booster vaccination at a dosage of 2 Lf (flocculation units) was given and the immune response measured. We found that prior to the booster vaccination 174 (87%) of the study group had an antibody level ≥0.1 IU/ml, 16 (8%) had an antibody level of ≥0.06 IU/ml and ≤0.09 IU/ml, and 10 (5%) had an antibody level of ≤0.05 IU/ml. At the 10th day after the booster vaccination 185 (99%) acquired antibody level 20.1 IU/ml, and at the 28th day all the vaccinees had antibody level above 0.1 IU/ml. When comparing the anamnestic and the delayed reaction to the booster vaccination, no significant difference was found between the group that prior to the vaccination had antibody level ≤0.05 IU/ml and the group with antibody level ≥0.06IU/ml and ≤0.09 IU/ml. Side effects were mainly local: 76 (38%) of the vaccinees had moderate local pain at the site of the injection and 40 (20%) had severe local pain. Abduction limitation of the injected arm was reported by 17 (8%) of the subjects. Weakness was reported by 67 (33%), headache by 18 (9%) and fever by 2 (1%) subjects. We conclude that antibody levels 20.1 IU/ml are protective and booster vaccination at a dosage of 2 Lf raises the antibody levels to protective levels in all the vaccines.