Acellular pertussis vaccines provide protection against pertussis with few adverse effects. Differences in the reactogenicity and immunogenicity of available pertussis vaccines may be influenced by the immunisation schedule employed. We assessed responses to an acellular pertussis, diphtheria, tetanus vaccine mixed with Haemophilus influenzae type b (Hib) vaccine, (PRP-T) given at age 2, 3 and 4 months. Parents kept a symptom diary for 3 days after each immunisation. Antibodies to diphtheria, tetanus, pertussis toxin and filamentous haemagglutinin were measured by enzyme immunoassay at 2 and 5 months. Results were compared with historical controls who received a combination whole-cell pertussis, diphtheria, tetanus/PRP-T vaccine in the same schedule. A total of 262 infants were recruited, of whom 251 were fully evaluated after three doses of vaccine. Systemic and most local reactions were less frequent following the acellular combination. Fever > or = 38 degrees C was reported after only 0.6% of doses. Redness or swelling > or = 2.5 cm were unusual after the first two doses (2-5%), but rates rose to 13% after the third dose. Antibody responses to diphtheria and tetanus toxoids were lower, while those to pertussis antigens were higher, more uniform and less attenuated by pre-immunisation antibody than in infants who received the whole-cell combination. All infants achieved protective antibody titres of at least 0.1 IU/ml for diphtheria and 0.01 IU/ml for tetanus.
Conclusion: The acellular combination vaccine was immunogenic for diphtheria, tetanus and pertussis components and was associated with low rates of fever following immunisation.