Levels and avidity of antibodies to tetanus toxoid in children aged 1-15 years in Dar es Salaam and Bagamoyo, Tanzania

A study was undertaken to determine the serological response in children (a ged 1-15 years) immunized with diphtheria-pertussis-tetanus vaccine (DPT) a lone or with a tetanus toroid (TT) booster dose under the Expanded Programm e on Immunization in Dar es Salaam and Bagamoyo, Tanzania. Using an ELISA t echnique, serum levels of anti-TT antibody, antibody avidity and anti-TT Ig G subclasses were determined in 138 apparently healthy children. Our findin gs revealed that 94.7% and 98% of children aged 1-5 years in Dar es Salaam and Bagamoyo, respectively, had anti-TT antibody levels above that consider ed protective (greater than or equal to 0.1 IU/ml). Among 6-15-year-old chi ldren, 53.3% in Dar es Salaam and 55% in Bagamoyo had anti-TT antibody leve ls greater than or equal to 0.1 IU/ml. The avidity index of anti-TT antibod ies was high in most of the younger children, 84.2% in Dar es Salaam and 92 % in Bagamoyo. Significantly fewer older children in Dar es Salaam and Baga moyo (53.3% and 50%, respectively) had high avidity index antibodies. The p redominant anti-TT IgG subclasses were IgG(1) and IgG(3). It is concluded t hat the current DPT immunization schedule provides adequate tetanus immunit y for children under 5. However, about half of the older children had no pr otection against tetanus.