At the start of a pandemic, all humans are immunologically naïve if the nascent virus contains antigenically novel HA and NA subtypes. In the event of a pandemic, the need for an effective vaccine is unequivocal. This study will test the safety, infectivity, and immunogenicity of a live-attenuated pandemic virus vaccine. The study will be an open-label, inpatient trial that will be initiated between April 1st and December 20th of each calendar year, when wild-type influenza virus is unlikely to be circulating in the community. Eligible participants will attend a study screening, which includes medical history, physical examination, hematology testing, liver and renal function testing, H7N7 antibody titer, HIV and Hepatitis B and C screening, urine dipstick testing (with possible urinalysis in the event of an abnormal urine dipstick result), and urine drug toxicology testing. Female participants of child-bearing age may also have a pregnancy test.