Patient description: A 42-year-old healthy woman came to the clinic to have her flu shot in early October. She works in a rehab center and has no underlying disease. It's her first time getting the vaccine this year. She is married for 5 years and uses barrier methods of contraception. Her menstrual cycle is irregular. She does not smoke. She is not on any medications. She exercises regularly for 30 minutes a day at least 5 days a week. She has no history of allergies to any food or drugs. Her past surgical history is significant for tonsillectomy and she is otherwise healthy.

Clinical trial eligibility criteria: eligible ages (years): 18.0-45.0,  Influenza Influenza, Human Vaccine Reaction Influenza A Influenza Type B Influenza A H1N1 Influenza A H3N2 Provide written informed consent prior to initiation of any study procedures Are able to understand and comply with planned study procedures and be available for all study visits Are males or non-pregnant females, 18-45 years of age, inclusive Are in overall good health. (As determined by medical history and physical examination to evaluate acute or currently ongoing chronic medical diagnoses that could affect the assessment of the immunogenicity of influenza vaccine.) Women of childbearing potential (not sterilized via tubal ligation, bilateral oophorectomy, salpingectomy, hysterectomy, or successful metal coil placement (permanent, non-surgical, non-hormonal sterilization) with documented radiological confirmation test at least 90 days after the procedure, and still menstruating or <1 year of the last menses if menopausal.) must use an acceptable contraception method (includes, but is not limited to, non-male sexual relationships, abstinence from sexual intercourse with a male partner, monogamous relationship with vasectomized partner who has been vasectomized for 180 days or more prior to the subject receiving vaccination, barrier methods such as condoms or diaphragms with spermicide or foam, effective intrauterine devices, NuvaRing®, and licensed hormonal methods such as implants, injectables, or oral contraceptives ("the pill")) from 30 days before vaccination until 30 days after vaccination Women of childbearing potential must have a negative urine or serum pregnancy test within 24 hours prior to vaccination  Have an acute illness (an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the site principal investigator or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol) as determined by the site principal investigator or appropriate sub-investigator, within 72 hours prior to vaccination Have any medical disease or condition that, in the opinion of the site principal investigator or appropriate sub-investigator, is a contraindication to study participation Have immunosuppression as a result of an underlying illness or treatment, a recent history or current use of immunosuppressive or immunomodulating disease therapy Use of anticancer chemotherapy or radiation therapy (cytotoxic) within 3 years prior to vaccination Have known active neoplastic disease or a history of any hematologic malignancy. Non-melanoma, treated, skin cancers are permitted Have known human immunodeficiency virus (HIV), hepatitis B, or hepatitis C infection Have known hypersensitivity or allergy to components of cell-cultured influenza vaccine Have a history of severe reactions following previous immunization with licensed or unlicensed influenza vaccines Have a history of Guillain-Barre Syndrome Have taken oral or parenteral (including intra-articular) corticosteroids of any dose within 30 days prior to vaccination