Text Box: SAFETY, TOLERABILITY AND IMMUNOGENICITY OF AN EXTEMPORANEOUSLY COMBINED DTwPHIB (DIPHTHERIA, TETANUS, wPERTUSSIS, HAEMOPHILUS INFLUENZAE TYPE B-CRM197 CONJUGATE) VACCINE Kanra G1, Marchetti E2, Viviani S2, Nacci P2, Yalçin S1, Demiralp O3, Bilgili N3, Kara A1, Mutlu B4, Yurdakök K1 and Podda A2 1Department of Pediatric Infectious Diseases, Medical Faculty, Hacettepe University, Ankara, Turkey 2Clinical Research, Chiron Vaccines, Siena, Italy 3Gülveren Health Centre, Ankara, Turkey 4Chiron Vaccines, Berk Ilac Ith, Ankara, Turkey Objective: To compare separate but concomitant administration of Chiron DTwP vaccine and Chiron Hib-CRM197 conjugate vaccine with a combined Chiron DTwPHib vaccine obtained by extemporaneously mixing of Hib lyophilized conjugated (Vaxem Hib®) and Chiron Behring DTP® liquid vaccines. Methods: A total of 320 infants were enrolled at Gülveren Health Centre, Ankara, Turkey, and randomised in a 1:1 ratio to receive at 2, 3 and 4 months of age either separate administration of DTwP and Hib vaccines or the combined DTwPHib vaccine. Results: Local and systemic reactions were mild and similar in both vaccine groups. No serious adverse events were reported. In the combined DTwPHib recipient group 100% of subjects had anti-PRP antibodies ≥0.15 mg/mL while in the separate DTwP and Hib vaccine group this percentage is 98%. A higher proportion of subjects who received the combined DTwPHib vaccine were protected in the long term compared with subjects who received separate vaccines (anti-PRP ≥1 mg/mL 98%vs93%). Similarly, Geometric Mean Titres (GMTs) were significantly higher in recipients of the DTwPHib vaccine than in recipients of separate vaccines (23 mg/mL vs 8.78 mg/mL). The proportion of subjects who seroconverted to Agg2 and 3 was higher in recipients of separate vaccines than in recipients of the combined DTwPHib vaccine (85%vs79%). All subjects were protected against diphtheria and tetanus. Conclusions: The extemporaneously combined DTwPHib vaccine was safe and immunogenic as primary vaccination in infants. In addition immunoresponse to Hib vaccine was particularly enhanced in subjects immunised with the combined vaccine compared with separate administration. 2414