Study of Immune Responses After Vaccination Against Seasonal Influenza Virus and Against Influenza H1N1-v Pandemic Virus in a Medical Staff.

This project may help to answer several fundamental questions related to public health regarding vaccination against influenza viruses and regarding the influenza A(H1N1)v pandemy: What is the immunologic efficacy in terms of antibodies response of the vaccination against the seasonal (2009-2010) influenza virus and against the A(H1N1)v virus in the clinical staff? Moreover, it may help to answer questions related to the use of a vaccine against influenza virus variants emerging in the French population: 1. Before the vaccination: * What is the status of the residual anti-H1N1 seasonal viruses immunity and of the anti-A(H1N1)v immunity in the population stratified by age and taking into account the multiplicity of the prior seasonal vaccinations? * What is the level of the cellular and humoral cross-reactivity between the different H1N1 strains? 2. After the vaccination: * What is the intensity of the anti-vaccine immune response as a function of the age of the population ad of the prior seasonal vaccinations? * What is the level of the cellular and humoral cross-reactivity after vaccination as a function of the age of the population and of the multiplicity of the prior seasonal vaccinations?

Inclusion Criteria: * Healthy volunteers * Age superior or equal to 20 years * Women with childbearing potential using contraception Exclusion Criteria: * Documented immune depression * Current immunosuppressive therapy * Pregnancy (documented by a positive pregnancy test) * Breast feeding women * Documented allergy or hypersensitivity to vaccines * Documented acute or chronic inflammatory disease * Concomitant participation to another clinical trial