This study will last approximately 90 days. Participation in this study includes two 12-day hospital stays in an isolation unit at the Johns Hopkins Bayview Medical Center. All participants will receive two doses of vaccine in nasal spray form, at study entry and sometime between 4 and 8 weeks after initial vaccination. Participants will be admitted to the isolation unit 2 days prior to each vaccination. A targeted physical exam, vital signs measurement, and a nasal wash will occur daily following each vaccination until discharge. Participants will be discharged after three consecutive nasal washes on or after Day 6 are negative. Blood and urine collection will occur at selected timepoints throughout the study. A follow-up outpatient visit will occur approximately 4 weeks following each vaccination.