RANDOMIZED CONTROLLED TRIAL OF ACELLULAR DIPHTHERIA, PERTUSSIS AND TETANUS VACCINES IN SOUTHERN GHANA

A randomized controlled trial of acellular diphtheria/pertussis/tetanu s (ADPT) freeze-dried and liquid vaccines in infants was conducted in a peri-urban community (Ashaiman) in southern Ghana. Immunogenicity of the acellular vaccines, persistence of antibodies and adverse reactio ns were compared with those achieved with a whole-cell diphtheria-pert ussis-tetanus (DPT) vaccine. The incidence of pertussis in the vaccine groups and prevalence of pertussis in children under 5 years of age i n the study area were also determined. The acellular vaccines produced significantly fewer local and systemic reactions. Local reactions suc h as swelling and redness were observed in 2% (8/399) to 2.3% (9/385) of the acellular vaccine recipients as against 31% (122/394) in the wh ole-cell vaccine group. Fever (greater than or equal to 37.5 degrees C ) occurred in 7.27% (29/399) to 9.8% (38/385) in the acellular vaccine groups compared with 36.6% (145/394) in the whole-cell vaccine group. Geometric mean titres (GMTs), measured by ELISA, to pertussis toxin ( PT) and filamentous haemagglutinin (FHA) were significantly higher in the acellular vaccine groups than in the whole-cell DPT (WCDPT) group. There were no significant differences in the GMTs of tetanus and diph theria antitoxins between the two groups after each vaccination. Twelv e months after primary vaccination, GMTs to PT in the freeze-dried, li quid ADPT groups and the WCDPT group have fallen from 56.23, 62.63 and 44.97 ELISA U/ml to 6.08, 6.18 and 11.30 ELISA U/ml, respectively. GM Ts to FHA in all the vaccine groups also dropped during the same perio d from 49.94, 41.73 and 20.74 ELISA U/ml to 7.26, 7.72 and 5.91 ELISA U/ml, respectively. In this comparative controlled trial, the ADPT vac cines were more immunogenic, with less local and systemic reactions, t han the WCDPT vaccine but there was a considerable drop in antibody ti tres in all the vaccine groups 12 months after primary vaccination. Ho wever, the levels of titres of anti-PT and anti-FHA antibodies in all the three vaccines that confer protection are not known. Further studi es are necessary to provide this information in order to assess the ne ed for subsequent booster doses after primary immunization with both A DPT and WCDPT vaccines.