 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 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. 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. The primary objective of the study is to characterize HA-specific plasmablasts and memory B cells after influenza vaccination. 