Persistence of antibody after accelerated immunisation with diphtheria/tetanus/pertussis vaccine.

OBJECTIVE To determine the persistence of antibody to diphtheria, tetanus, and pertussis in children receiving an accelerated schedule of primary immunisation. DESIGN Controlled study of antibody testing of blood samples from children immunised according to various schedules: three doses of triple vaccine completed at 8-13 calendar months, 6-7 calendar months, before 6 calendar months, or three doses followed by diphtheria/tetanus before age 2. SETTING Plymouth Health Authority. SUBJECTS 129 children aged 4 years who had received three doses of diphtheria/tetanus/pertussis vaccine with or without a diphtheria/tetanus booster. MAIN OUTCOME MEASURES Diphtheria and tetanus antitoxin concentrations and antibody titres to pertussis toxin, filamentous haemagglutinin, and agglutinogens 2 and 3. RESULTS All children had protective concentrations of antitoxin to diphtheria and tetanus (greater than or equal to 0.01 IU/ml). There was no evidence of a significant difference in diphtheria or tetanus antitoxin concentrations and pertussis antibody titres in children immunised with an accelerated course (third dose of triple vaccine before 6 months) compared with those who received a longer course (third dose at 8-13 months) with no booster (geometric mean antitoxin concentration 0.411 (95% confidence interval 0.273 to 0.618) v 0.426 (0.294 to 0.616) for diphtheria and 0.358 (0.231 to 0.556) v 0.299 (0.197 to 0.453) for tetanus; geometric mean antibody titres 903 (500 to 1631) v 1386 (848 to 2266) for pertussis filamentous haemagglutinin, 179 (130 to 248) v 232 (167 to 322) for pertussis toxin, and 2002 (1276 to 3142) v 3591 (2220 to 5809) for agglutinogens 2 and 3). CONCLUSION Immunisation with three doses of triple vaccine at monthly intervals completed before 6 months of age probably provides adequate protection against diphtheria, tetanus, and whooping cough which will persist until the age of the preschool booster.