This study will compare the different immune responses to Influenza A (H5N1) Virus Monovalent Vaccine with and without the AS03 adjuvant. The Influenza A (H5N1) Virus Monovalent Vaccine with AS03 adjuvant vaccine is approved for use for adults to protect against flu caused by the A/H5N1 "bird flu" virus in Europe but none of the vaccines to be used in the study are approved for use in the United States. The results of this study will help researchers learn about better ways to vaccinate people against the H5N1 flu.