This study will last from approximately 6 weeks, up to a maximum of approximately 20 weeks. Participation includes a 10-day minimum hospital stay in an isolation unit of the Bayview Medical Center of Johns Hopkins University. Participants will be admitted to the isolation unit 2 days prior to vaccination. At vaccination, participants will be given one dose of the H9N2 (6-2) AA ca Reassortant (A/Chicken/Hong Kong/G9/97 x A/Ann Arbor/6/60 ca) vaccine in the form of nose drops. Each day for the next 7 days, participants' vital signs will be monitored and nasal washes will be collected to test for the presence of vaccine virus. Participants may be discharged from the hospital after 3 consecutive negative viral cultures, but not before Day 7 after vaccination. Follow-up visits will occur on Days 21, 28, and 42, and will include blood collection and a physical exam.