The Immunologic Basis for an Attenuated Immune Response to the Influenza Vaccine After Repeated Annual Vaccination

Inclusion Criteria: * Capable of informed consent and provision of written informed consent before any study procedures. * Capable of attending all study visits according to the study schedule. * Are in good health, as determined by medical history and targeted physical exam related to this history. * Oral temperature is less than 38 degrees Celsius. * Resting pulse rate is between 50 and 115 beats per minute. * Female subjects of childbearing age must have a negative urine pregnancy test within 24 hours before study vaccination. * Have received the influenza vaccine at least 3 of the past 5 years or have received the influenza vaccine in 2 or less of the past 5 years. Exclusion Criteria: * Have an acute illness within 72 hours before vaccination. * Have any condition that, in the opinion of the principal investigator, would place the subject at an unacceptable risk of injury or confound the interpretation of the study results. * Have any acute or chronic medical condition that, in the opinion of the principal investigator, would make vaccination unsafe or interfere with the evaluation of immune response to study vaccination. * Have a suppressed immune system as a result of illness, immunosuppressive medication, chemotherapy, or radiation therapy within 3 years prior to study vaccination. * Have known HIV, hepatitis B, or hepatitis C infection. * Have a known history of autoimmune disease. * Have taken oral or parenteral corticosteroids of any dose within 30 days before study vaccination. * Have taken high-dose inhaled corticosteroids within 30 days before study vaccination. * Have received any licensed live vaccine within 30 days or any licensed inactivated vaccine within 14 days prior to study vaccination. * Have planned vaccination with any vaccine during the 29-day duration of subject study participation. * Have received immunoglobulin or other blood products, with the exception of Rho D immunoglobulin, within 90 days prior to study vaccination. * Have donated blood or blood products within 30 days before study vaccination, plan to donate blood at any time during the 29-day duration of subject study participation, or plan to donate blood within 30 days after the last blood draw. * Have known hypersensitivity or allergy to eggs, egg protein, chicken protein, or other compounds of the study vaccine. * Have a history of severe reactions following vaccination with influenza virus vaccines