Safety and immunogenicity of combined or associated administration of PRP-T vaccine with diphtheria, tetanus and pertussis vaccine in Thai children.

To assess whether the combination of a diphtheria, tetanus and pertussis vaccine with a Haemophilus influenzae type b conjugate vaccine (PRP-T) had any effect on immunogenicity or safety compared with separate administration of the vaccines, 158 infants were randomized to receive the vaccines either in association or as a combination at 2, 4, and 6 months of age. A total of 126 infants (59 associated, 67 combination) completed the three-dose regimen and were analysed for immunogenicity and safety. With respect to safety, there were no significant differences between the two groups. The combination vaccine was well tolerated with adverse reactions consisting mainly of transient pain, redness, induration and some low-grade fever. With respect to immunogenicity, response to PRP-T vaccine was good. Following just two doses, all infants achieved anti-PRP titers >0.15 microg/ml, regardless of whether the vaccine was given in combination or association. Following three doses, 98.5 per cent of infants in the combination group and 98.3 per cent in the association group had titers higher than 1.0 microg/ml.