This study is the first step in a clinical research program that aims to study the immune response to influenza vaccine in the elderly and then to propose a new method of administering the vaccine.

Influenza can cause severe complications in patients at risk (elderly and subjects vulnerable because of a chronic underlying disease). Over 90% of deaths related to influenza occur in people aged over 65 years.

Vaccination is the most effective way to prevent infection. The World Health Organization recommends annual immunization for people at risk, including all persons aged over 65 years, to reduce the risk of morbidity and mortality related to influenza.

However, the immune response to influenza vaccine appears to be lower in elderly than in young people.

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