Respiratory Syncytial Virus Human Challenge in Healthy Adult Volunteers

Background: \- Respiratory syncytial virus (RSV) can cause respiratory infections. Some of these can be life-threatening, especially in young children, the elderly, and people with weak immune systems. Researchers want to study RSV infection in a hospital setting in healthy adults. They want to use what they learn to test new treatments or vaccines in the future. Objectives: \- To study how the body responds to RSV. Eligibility: \- Healthy volunteers ages 18-50 Design: * Participants will be screened under another protocol. * Participants will have: * Medical history * Physical exams * EKG. Heart rhythm is measured with small sticky patches on the chest, arms, and legs. * Chest x-ray * Pulmonary function tests. This measures how much air a person can move into and out of the lungs. * Blood and urine tests * Nasal washes and/or nasal swabs. For the wash, the nose will be rinsed with a sterile liquid. For the swab, the inside of the nostril will be rubbed with a cotton swab. * Participants will have two, possibly three, follow-up outpatient visits, approximately 1, 2 and 6 months after receiving the dose of RSV. * Participants will stay in the hospital under isolation for 7 or more days after getting the virus. * The average stay is 10 days. Participants cannot leave the isolation unit. They cannot have visitors. * The virus should cause a mild to medium cold. * Participants will fill out a symptom card every day in the hospital and for 1 month after. * Participants will have 2 follow-up visits, 28 and 56 days after leaving the hospital. * Female participants who are sexually active must remain abstinent or use an effective form of birth control for 1 month before and after getting the virus.