Neutralizing antibodies in 6-year-old children after five doses of tetanus toxoid.

It has recently been suggested that multiple boosters of tetanus toxoid may enhance serum antitoxin titres but may not necessarily lead to an effective immune response. Tetanus antitoxin titres by haemagglutination inhibition and mouse toxin neutralization tests were determined in sera of 64 children, 5 and 6 years old. Primary vaccination against tetanus was given as four doses of diphtheria-pertussis-tetanus (DPT) vaccine beginning in the second or third month of life, and a booster dose given to schoolchildren at 6 years of age. In our area more than 90% of children receive five doses of tetanus toxoid before their seventh birthday. The children were given 0.5 ml of DPT or DT containing 10 Lf ml-1 tetanus toxoid at each injection. The haemagglutination titres and the toxin neutralization titres were much higher in 6-year-old than in 5-year-old children. We concluded that the fifth dose is an effective booster in 6-year-old children.