Safety and immunogenicity of different formulations administered as a 2-dose schedule in children 6-35 months of age will be evaluated. In addition, the quality of the 2-dose priming will be assessed through the anamnestic response elicited by an antigen challenge (unadjuvanted H5N1) administered 12 months later. The persistence of the immune response approximately 12 months (Day 385) after dose 2 will also be evaluated.