ABSTRACT
We performed a double-blind clinical study to evaluate the safety and immunogenicity of four formulations of a DTwPHib full liquid vaccine, three of which contained fractional doses of the 10 microg-dose of CRM197-Hib conjugate vaccine. A total of 261 infants were enrolled and randomised to receive at 3, 4 and 5 months of age, in a double-blind fashion, one of the four DTwPHib vaccine formulations containing 10, 5, 2.5 or 1.25 microg of CRM197-Hib conjugate. Post-immunization reactions were similar in the four vaccine groups, they were mild, transient and resolved without sequelae. The seroconversion rates to anti-PRP titres > or = 0.15 microg/mL were 100%, 98%, 97% and 98% in the groups 10, 5, 2.5 and 1.25 microg, respectively. The seroconversion rates to anti-PRP titres > or =1 microg/mL were 95%, 97%, 88% and 90%, again respectively. Anti-PRP GMTs were 18, 17, 7.82 and 6.94 microg/mL, respectively. All subjects were protected against tetanus and diphtheria, and >80% seroconverted to pertussis. High, and similar, levels of anti-PRP GMTs were elicited by the formulations with 10 and 5 microg of CRM197-Hib conjugate. Although the formulations with 2.5 and 1.25 microg of CRM197-Hib elicited lower levels of anti-PRP GMTs, they were immunogenic and are possible candidates for further development.
