 This is an open label, single arm, observational study of longitudinal immunologic responses to influenza vaccine in healthy adult subjects. This study will enroll males and non-pregnant females, 18-49 years old. The study duration is 6 years and participant duration of 180 days. The subjects will be screened at enrollment with a history and physical exam and laboratory testing to ensure they are healthy enough to participate. Qualifying subjects will be vaccinated with an FDA approved seasonal inactivated influenza vaccine IIV according to the package insert. Approximately 450 ml of blood will be collected for the research assays during the course of the study. Specifically, 16 ml will be collected for screening; 48ml will be collected at enrollment; 96ml will be collected at visit days 7 and 14; and 64 ml will be collected at 28, 90, and 180 days post vaccination. The study will enroll 10 healthy volunteers per vaccination season in years 1, 2, and 4 through 6 of this study, for a total enrollment of 50 subjects. Individuals who complete the study will be given the option to re-enroll in subsequent years as long as they continue to meet all inclusionexclusion criteria. Re-enrolling subjects will be re-consented, given new subject identifiers, and counted towards the enrollment number goal for each year of participation. The primary objective of the study is to characterize HA-specific plasmablasts and memory B cells after influenza vaccination and secondary objective investigate the longevity of humoral immunity to influenza virus in humans. 