Adjuvanted Influenza Vaccine Effectiveness in the Elderly (65+Yrs)

Inclusion Criteria: 1.Elderly tested for influenza as part of routine clinical care in the Lower Mainland and on Vancouver Island during the influenza season. Cases: Proven influenza diagnosed on naso-pharyngeal swab via PCR Controls: Elderly with influenza-like-illness testing negative for influenza during the influenza season. Exclusion Criteria: 1. Known immunodeficiency disorders (including HIV) 2. Current or recent (within 90 days prior to first dose of influenza vaccine) immunosuppressive treatment including chronic oral steroids (1mg/kg for \> 4 weeks), cytotoxic chemotherapy, radiation therapy, other immunosuppressive drug and biologic agents Note: Use of topical or inhalant corticosteroids is acceptable. 3. Administration of immunoglobulins during the study period;