Immune Responses in Health Care Personnel

Inclusion Criteria: * Members of health care or laboratory personnel in HUS having decided to take the seasonal influenza vaccination by the routine occupational health care service * General good health as established by or volunteer's own statement * Written informed consent * Presumably able and willing to participate in the study during the starting influenza season Exclusion Criteria: * Any confirmed or suspected immunosuppressive or immunodeficient condition, including human immunodeficiency virus (HIV) infection. * Administration (longer than 14 days) of immunosuppressants or other immune- modifying drugs within 6 months before the vaccination; oral corticosteroids in dosages of 20 mg/day or more prednisolone or equivalent are excluded; inhaled or topical steroids are allowed. * Pregnancy or lactation * Acute disease at the time of enrolment (defined as the presence of a moderate or severe illness with or without fever) * Contraindication for influenza vaccination * Any other criteria which, in the investigator's or dedicated study staff member's opinion, would compromise the ability of a subject to participate in the study, a subject's well-being, or the outcome of the study