Clinical Trial Evaluating Efficacy and Safety of One Dose Versus Two Doses of Influenza Vaccination

The purposes of this study are: 1. Evaluate the efficacy and safety of a double dose of seasonal flu vaccine compared to a single dose. 2. Determine the specific cellular immune response produced after the first and second vaccine doses of seasonal flu vaccine by in vitro stimulation of specific memory cells (A and B flu viruses). 3. Evaluate the humoral immune response produced after one dose vs two doses of seasonal flu vaccine by the measure of serum antibody levels. 4. Evaluate clinical efficacy of stationary flu vaccine in solid organ transplant recipients. 5. Evaluate a long term cellular and humoral response(1 year) of seasonal flu vaccine. 6. Characterize the genetic expression profile of immune response after the flu vaccine in solid organ transplant recipients by means of a genetic sub-study. 7. Characterize the flu vaccine effect (one dose and two doses) through the antibody anti-HLA(human leukocyte antigen), and its influence on the rejection rate in solid organ transplant recipients, by means of immunologic sub-study.