ANTIBODY-RESPONSE TO ACCELERATED IMMUNIZATION WITH DIPHTHERIA, TETANUS, PERTUSSIS-VACCINE

From May, 1990, a new schedule of immunisation against diphtheria, tet anus, and pertussis (at 2, 3, and 4 months) replaced the previous more widely spaced schedule. A report that children had lower concentratio ns of diphtheria and tetanus antibodies a month after an accelerated s chedule led us to undertake a controlled study to assess antibody resp onse and the persistence of antibodies a year after immunisation in ch ildren receiving vaccine according to widely spaced and accelerated sc hedules. Concentrations of antibodies to diphtheria and tetanus toxoid s and to Bordetella pertussis filamentous haemagglutinin (FHA) were me asured by solid-phase radioimmunoassay (SP-RIA). We studied 57 childre n who received accelerated immunisation at median ages of 11, 16, and 21 weeks and two control cohorts (total n = 82) who received vaccine a t median ages of 15, 21, and 45 weeks. 6-8 weeks after the third dose the accelerated-schedule group had lower (p<0.0001) geometric mean con centrations of antibody to tetanus (0.522 [95% CI 0.383-0.710] vs 3.43 [2.45-4.81] IU/mL), diphtheria (0.266 [0.179-0.396] vs 2.39 [0.616-3. 53] IU/mL), and FHA (0.044 10.030-0.063] vs 0.270 [0.196-0.374] units/ mL) than the longer-schedule group. 12 months after the third dose the differences between the groups had narrowed (tetanus 0.197 vs 0.341 I U/mL, p=0.29; diphtheria 0.100 vs 0.131 IU/mL, p=0.64; FHA 0.014 vs 0. 016 units/mL, p=0.72). At that time all children had tetanus antibody concentrations above protective levels (0.01 IU/mL); only 2 of 31 in t he accelerated-schedule group and 3 of 31 in the longer-schedule group had diphtheria antibody concentrations below the protective level. Th e use of an accelerated schedule of diphtheria, tetanus, and pertussis vaccination is unlikely to lead to an increase in the proportion of c hildren unprotected against these diseases before the preschool booste r.