Challenge Infection of Healthy Adult Volunteers With RSV A2

* INCLUSION CRITERIA: 1. Age 18-50 years inclusive. 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 (e.g., 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, must 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, they must also use a barrier method 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 180 days prior to first dose of study agent 6. A plaque reduction RSV neutralization titer \< 8.0 log(2). EXCLUSION CRITERIA: 1. Subject who was previously challenged with RSV A2. 2. Female subject who is pregnant or lactating OR planning to become pregnant from 30 days prior to inoculation through 30 days after inoculation. 3. Presence of self-reported or medically documented significant medical condition(s) including but not limited to: -Respiratory disease (e.g., chronic obstructive pulmonary disease, emphysema, rhinitis, sinusitis) in adulthood, and additionally: --A history of asthma within the past 5 years, or a current diagnosis of asthma or reactive airway disease associated with exercise, seasonal hay fever or allergic rhinitis --Presence of any febrile illness or symptoms suggestive of a respiratory infection within 2 weeks prior to inoculation. * Any significant abnormality of the nose or nasopharynx, including recurrent epistaxis within 90 days prior to viral inoculation or nasal or sinus surgery within 180 days prior to viral inoculation. * Chronic cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease). * Chronic neurological or neurodevelopmental conditions (e.g., cerebral palsy, epilepsy, stroke, seizures). * Ongoing malignancy. * Chronic medical condition requiring close medical follow-up or hospitalization during the past 5 years (e.g., diabetes mellitus, renal dysfunction, hemoglobinopathy, autoimmune disease). * An immunodeficiency. 4. Use of systemic corticosteroids exceeding 10 mg/day of prednisone equivalent and nasal steroid preparations or immunosuppressive drugs within 30 days before inoculation and within 60 days after. Low dose topical steroid preparations used for a discrete period of time are permitted. 5. Inhaled bronchodilator or inhaled steroid use within the last 360 days or use after upper respiratory tract infections. 6. 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. 7. Complete blood count (CBC), aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine values or other screening labs or tests (e.g. electrocardiogram (EKG), chest x-ray (CXR)) are outside of the NIH Department of Laboratory Medicine normal reference range and deemed clinically significant by the PI. 8. Positive FDA-approved HIV test obtained during screening procedures. 9. Positive serology for hepatitis C virus obtained during screening period. 10. Presence of hepatitis B surface antigen obtained during screening period. 11. A smoker of tobacco products or a routine marijuana smoker currently or in the past year. 12. Current alcohol abuse or addiction. 13. Current illicit drug abuse or addiction. 14. Receipt of a licensed vaccine within 30 days prior to RSV A2 inoculation and planned vaccination within 60 days after inoculation.. 15. Receipt of blood or blood-derived products (including immunoglobulin) within 180 days 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. 16. Receipt of an investigational agent or vaccine within 90 days prior to scheduled RSV A2 inoculation and planned receipt within 60 days after inoculation. 17. A body mass index (BMI) less than or equal to 18.5 or greater than or equal to 37.0. 18. A medical, occupational, or family problem that would preclude the participant from complying with all study requirements. 19. Shares household, works closely with, or has routine contact with a child (children) \< 5 years of age or with immunocompromised individual(s), adult(s) with significant cardiopulmonary disease or asthma, institutionalized persons or persons 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. 20. Deprived of freedom by an administrative or court order or in an emergency setting. 21. Any condition that in the opinion of the 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.