Following vaccination, all participants will remain on the isolation unit for at least 9 days. Physical examination and test of NW for influenza virus culture will be performed daily until discharge. They will be discharged once nasal wash (NW) specimens test negative for influenza for at least 2 consecutive days beginning on or after Day 7. Physical examination and NW for influenza virus culture will be performed daily until discharge. Participants will return for inpatient treatment 26 days after receiving their first dose of the vaccine. Two days later, or 28 days after the first vaccine, participants will receive a second dose of the influenza vaccine. Participants will then follow the same procedures as before, undergoing daily physical exams and testing of NW specimens. They will be eligible for discharge after another 9 days, provided their NW specimens test negative for influenza for 2 consecutive days.