A phase I prospective, randomized study in healthy adult subjects at a single center. Adult subjects age 18 to 47 years and meeting all enrollment criteria will choose to participate as subjects who receive inactivated vaccine followed by a live vaccine boost at 4 weeks (Group 1), 12 weeks (Group 2), or 24 weeks (Group 3), or to be in an observational group (Group 4) which will not be scheduled for a booster dose but may serve as a roll-over group for subjects who withdraw prior to the second vaccination but agree to remain in follow-up. A fifth group will receive two intramuscular doses of adjuvanted H7N9 pIIV separated by four weeks.