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): 18.0-49.0,  Healthy or Stable Underlying Chronic Medical Condition Male or female age 18 to 49 years, inclusive, on the day of randomization (reached his or her eighteenth year birthday but not yet reached his or her 50th year birthday) at the time of the dose of blinded investigational product Written informed consent and any locally required authorization obtained from the subject prior to performing any protocol-related procedures, including screening evaluations Females of child-bearing potential, (ie, unless surgically sterile [eg, bilateral tubal ligation, bilateral oophorectomy, or hysterectomy], had a sterile male partner, was at least 1 year post-menopausal, or practiced abstinence) must have used an effective method of avoiding pregnancy (including oral, transdermal, or implanted contraceptives, intrauterine device, female condom with spermicide, diaphragm with spermicide, cervical cap, or use of a condom with spermicide by the sexual partner) for 30 days prior to the first dose of investigational product, and must have agreed to continue using such precautions for 60 days after the dose of investigational product. In addition, the subject must also have had a negative urine or blood pregnancy test at screening and, if screening and Day 0 did not occur on the same day, on the day of vaccination prior to randomization. Investigator judgment was required to assess a female subject's capability of pregnancy Healthy by medical history and physical examination OR presence of stable underlying chronic medical condition for which hospitalization was not required in the previous year Able to complete follow-up period of 180 days post dose of vaccine as required by the protocol Subject available by telephone Able to understand and comply with the requirements of the protocol, as judged by the investigator  Acute illness or evidence of significant active infection at randomization Fever ≥ 100.4°F (38°C) at randomization History of asthma Any drug therapy from 15 days prior to randomization or expected drug therapy through 30 days post dose with the exception of contraceptives or chronic medications that were well tolerated and were not initiated and/or did not have a dosage change within 90 days of randomization Previous medical history or evidence of an intercurrent illness that might have compromised the safety of the subject in the study Current or expected receipt of immunosuppressive medications (inhaled and topical corticosteroids were permitted) including corticosteroids (≥ 20 mg/day of prednisone equivalent given daily or on alternate days for ≥ 14 days) within a 30-day window around dose of investigational product Note: topical corticosteroids for uncomplicated dermatitis were permitted according to the judgment of the investigator; topical calcineurin inhibitors were permitted in accordance with their package insert at entry and during study participation Receipt of immunoglobulin or blood products within 90 days before randomization into the study or expected receipt during study participation Receipt of any investigational drug therapy or standard vaccine within 30 days before the dose of investigational product in this study through 30 days after the dose of investigational product (use of licensed agents for indications not listed in the package insert was permitted) Any known immunosuppressive condition or immune deficiency disease including known or suspected infection with human immunodeficiency virus (HIV) History of allergic disease or reactions likely to be exacerbated by any component of the investigational product including allergy to eggs, egg proteins, gentamicin, or gelatin; or serious, life threatening, or severe reactions to previous influenza vaccinations