This study is an open-label, longitudinal study of healthy young women of reproductive age, not on hormonal contraception who receive seasonal inactivated influenza vaccine (IIV). The women will be followed for one menstrual cycle to measure luteinizing hormone surge, estradiol, and progesterone, and then vaccinated with the seasonal inactivated influenza vaccine prior to ovulation during a second month. At the investigator's discretion, or if there is active circulation of influenza virus in Baltimore, the investigators will vaccinate during the first menstrual cycle (prior to ovulation) and then follow for a second menstrual cycle for comparison. After vaccination, they will be followed for cytokine and chemokine responses as well as changes in the concentrations of steroid hormones. This study will evaluate the effect of IIV on inflammatory cytokines and hormonal responses before and after ovulation. Each woman will have 13 visits in addition to a screening visit, and will be followed for 2 complete menstrual cycles.