文本框: DTPa combinations: Challenges and solutions Dagan R Soroka University Medical Center, Beer Sheva, Israel The use of multivalent pediatric combination vaccines is providing an effective means of decreasing the number of injections necessary to protect children from multiple diseases. The lower reactogenicity of acellular pertussis (Pa) vaccines combined with diphtheria (D) and tetanus (T) toxoids make them the cornerstones of current pediatric combination vaccines, together with hepatitis B virus (HBV), inactivated poliomyelitis virus (IPV) and Haemophilus influenzae type b (Hib). While enormous benefits are associated with the ability to combine a range of antigens in one vaccine, there are also difficulties relating to the increasing formulation complexity. These include potentially unacceptable increases in reactogenicity, problems such as reduced formulation stability because of interactions between vaccine constituents, and immunological interference. Special attention has been focused on the antibody responses to all antigens in combinations, particularly the reduction in anti-polyribosylribitol phosphate (PRP) antibody concentration in Hib-containing formulations, in comparison to responses to the separate vaccines. While PRP antibody concentrations have been found to be lower following administration of DTPa-based Hib combinations, they still remain largely within the broad range published for licensed monovalent Hib conjugates and retain their quality and induction of immune memory. More elaborate combinations are still being considered but, today, the advent of a six-in-one vaccine represents a major milestone in efforts to achieve multiple protection against diseases in a more child-friendly way.