Immunity against tetanus and effect of revaccination 25-30 years after primary vaccination.

Fall off in tetanus immunity and the effect of late revaccination were investigated in a randomly selected group of Danes aged 25-30. Routine reinforcing doses of tetanus toxoid are not customary in Denmark except at injury and when there are certain occupational risks. 11% of the total group of 418 had antitoxin titres below that required for protection (ie, less than 0.01 IU/ml, determined by neutralisation technique). In those who had received only primary vaccination an exponential fall off in immunity was seen, and 25-30 years after primary vaccination, 28% had serum antitoxin concentrations below the level of protection. Up to 30 years after primary vaccination, one reinforcing dose of tetanus toxoid adsorbed by aluminium hydroxide was sufficient to induce protective titres of antitoxin. There were no serious side-effects and it was concluded that routine reinforcing doses of tetanus toxoid should be given before the age of 20 in Denmark and other countries where primary vaccination is given in the first years of life.