Respiratory Syncytial Virus Human Challenge in Healthy Adult Volunteers

* INCLUSION CRITERIA: 1. Age 18-50 years. 2. General good health, without significant medical illness, physical exam findings, or significant laboratory abnormalities as determined by the investigator. 3. Willingness to stay confined to the inpatient unit for required study duration. 4. Willingness to have samples stored for future research. 5. Subjects must be of non-childbearing potential (i.e., either surgically sterilized \[bilateral oophorectomy, bilateral tubal ligation, hysterectomy\] or, if of child-bearing potential and sexually active with a partner who can get them pregnant, then they must be have in place an effective method of contraception for at least 30 days prior to administration of the challenge virus and until 30 days after challenge virus administration: * intrauterine device (IUD) or equivalent * hormonal contraceptives (e.g., consistent, continuous use of contraceptive pill, patch, ring, implant or injection) * if participant uses contraceptive pill, patch or ring, two methods of contraception are required; a barrier method is to be used at the time of potentially reproductive sexual activity (e.g. male/female condom, cap, or diaphragm plus spermicide) * be in a monogamous relationship with a partner who has undergone a vasectomy at least 6 months prior to first dose of study agent. EXCLUSION CRITERIA: The presence of any one of the following criteria is sufficient to exclude a prospective subject from enrolling in this study: 1. Female subject is pregnant or lactating OR planning to become pregnant in the timeframe that begins 30 days prior to the inoculation and ends 30 days after inoculation. 2. Evidence of clinically significant neurologic, cardiac, pulmonary, hepatic, hematologic, rheumatologic, endocrine, autoimmune, or renal disease. 3. Complete blood count (CBC), AST, ALT, or creatinine values are both outside of the NIH Department of Laboratory Medicine normal reference range and deemed clinically significant by the PI. 4. Behavioral or cognitive impairment or psychiatric disease that in the opinion of the investigator affects the ability of the subject to understand and cooperate with the study protocol. 5. A medical, occupational, or family problem as a result of alcohol or illicit drug use during the past 12 months. 6. Routine smoker of a tobacco product or marijuana currently or in the past year. 7. Current alcohol abuse or addiction. 8. Current illicit drug abuse or addiction. 9. Presence of any febrile illness or symptoms suggestive of a viral respiratory infection within 2 weeks prior to inoculation accompanied by a positive multiplex FilmArray PCR performed on nasal wash. 10. Use of corticosteroids (including nasal preparations) or immunosuppressive drugs within 30 days before inoculation. 11. A history of asthma within the past 10 years, or a current diagnosis of asthma or reactive airway disease associated with exercise, seasonal hay fever or allergic rhinitis. 12. Positive FDA-approved HIV test result prior to inoculation. 13. Positive serology for hepatitis C virus within 6 months prior to inoculation. 14. Presence of hepatitis B surface antigen within 6 months prior to inoculation. 15. A known immunodeficiency syndrome. 16. Receipt of a licensed vaccine within 4 weeks prior to viral inoculation. 17. Receipt of blood or blood-derived products (including immunoglobulin) within 6 months prior to viral inoculation. Receipt of packed red blood cells given for an emergent indication in an otherwise healthy person, and not required as ongoing treatment is not exclusionary (for example packed red blood cells emergently given during an elective surgery). 18. Receipt of another investigational agent within 3 months prior to viral inoculation. 19. Individual with body mass index (BMI) less than or equal to 18.5 or greater than or equal to 37.5. 20. Any significant abnormality of the nose or nasopharynx, including recurrent epistaxis within 3 months prior to viral inoculation. 21. Nasal or sinus surgery within 6 months prior to viral inoculation. 22. Shares household, works closely with, or has routine contact with a child (children) \< 5 years of age or with immunocompromised individual(s), adults with significant cardiopulmonary disease, persons with significant asthma, institutionalized elderly or elderly with functional disability or any other individual that, in the judgment of the PI, might be at increased risk for complications if exposed to RSV. 23. Deprived of freedom by an administrative or court order or in an emergency setting. 24. Any condition that in the opinion of the principal investigator (PI) would jeopardize the safety or rights of a person participating in the trial or would render the person unable to comply with the protocol.