Immune Response Analysis to Influenza Vaccine in Elderly Aged Over 65 Years

Inclusion Criteria: * Subject aged 65 years or over * Influenza vaccination without adjuvant, within 3 weeks and 3 months before inclusion visit * Legal capacity to consent * Subject had given written consent before his participation Exclusion Criteria: * Adjuvanted influenza vaccine (e.g: Fluad, Gripguard) * Live vaccines within 3 weeks before and after influenza vaccination * Inactivated vaccines within 2 weeks before and after influenza vaccination * Chronic disease non-stabilized under treatment * Severe malnutrition in the opinion of the investigator * Congenital immunodeficiency * Chemotherapy or radiotherapy over the last 6 months * Immunosuppressive therapy or corticosteroid (daily dose of prednisone or equivalent \>/= 20 mg/d over 14 days) from 1 month before vaccination until the study visit * Participation in another clinical study that could interfere with the present study