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,  Influenza Maternal Subject Women age 18-49 years of age (inclusive) within 28-120 days of delivery Is in good health, as determined by vital signs (heart rate </=100 beats per minute (bpm); blood pressure: systolic <150 mm Hg; diastolic <90 mm Hg; oral temperature <100.0 degrees Fahrenheit), medical history and a targeted physical examination if indicated based on medical history Willing and capable of providing written informed consent for herself and infant Available for entire study duration, clinic visits and phone calls Planning on breast feeding from time of vaccination through 28 days post-vaccination. Breast milk must be at least one half of the source of the infant's feeding Willing to practice adequate contraception for at least 28 days after receipt of study vaccine if not surgically sterile via post-partum tubal ligation, bilateral oophorectomy or hysterectomy. Adequate contraception may but is not limited to, abstinence, monogamous relationship with a vasectomized partner, barrier methods such as condoms or diaphragms with spermicides, or licensed hormonal methods that are compatible with breastfeeding an infant May be reached by any IRB-approved form of communication during study period. May telephone, email, web based, social media, and/or text messaging, based on specific local IRB recommendations Agree to sign a medical release for herself and her infant (if needed) so that study personnel may obtain medical information about her or her infant's health. Infant The infant(s) should be in good health as assessed by medical history, interview, rectal temperature and a targeted physical examination based on medical history Infant born greater than or equal to 36 weeks gestation  Maternal Subject History of receipt of licensed influenza vaccine for the current influenza season. (If enrolled in 2011-2012 season [October 2011 February 2012], subject must not have received 2011-2012 influenza vaccine. If enrolled in the 2012-2013 season [July 2012 or later], subject must not have received 2012-2013 influenza vaccine) History of previous participation in this study Known allergy to eggs, egg proteins or other components in the vaccines (i.e. formaldehyde, polyethylene glycol, p-isooctylphenyl ether, sucrose, gelatin, polysorbate 80, gentamicin, arginine, sodium phosphate, sodium chloride, octylphenol ethoxylate, EDTA) If enrolled in the 2011-2012 season, known or suspected latex allergy. For the 2012-2013 season, known or suspected latex allergy is not a reason for exclusion History of severe reactions following immunization with contemporary influenza virus vaccines Received any other licensed vaccines within 14 days (for inactivated vaccines) or 28 days (for live vaccines) prior to vaccination in this study, or expects to receive a licensed vaccine during the 28 days after vaccination in this study Received an experimental/investigational agent (vaccine, drug, biologic, device, blood product, or medication) within 28 days prior to vaccination in this study, or expects to receive an experimental/investigational agent within the study time period (180 days after vaccination in this study) Received antiviral agent against influenza A and/or B within 48 hours prior to vaccination in this study. Antiviral agents should not be administered until 2 weeks after vaccination in this study unless medically necessary