Vaccine immunity to diphtheria: a 20-year follow-up study.

A cohort of close to 70 children born in 1967-68 was followed for estimations of serum antitoxin levels against diphtheria. During the first 3-year-period after vaccination the mean level declined from 0.05 international units (IU) to 0.03. From the year before to the year after the booster of 0.5 LF of toxoid was given at the age of 8 years, the mean level raised from 0.01 to 0.06 IU. At 18 years the mean was again down to 0.01. Between 18 and 23 years of age a difference between the sexes was seen (higher levels in men). The explanation of this phenomenon must be the extra booster given to those young men who have done their compulsory military service.