Randomised, double-blind, placebo-controlled study to evaluate the safety, tolerability, immunogenicity and shedding of live-attenuated RSV vaccine in healthy adults

1. Healthy male or female, 18-50 years of age, inclusive at screening;
2. Body mass index (BMI) * 18.0 and < 32.0 kg/m2;
3. Good health, based upon the results of medical history, physical examination, vital signs, ECG, and laboratory profiles of both blood and urine;
4. Pre-existing virus neutralization antibody titers (VNT) against RSV * 9.6 log2 (titer) at screening;
5. Willing to comply with effective contraception during the study if subject is male or woman of child bearing potential, up to 90 days after the vaccine administration;
6. Signed informed consent prior to any study-mandated procedure;
7. The ability to communicate well with the Investigator in the Dutch language
8. Willing to comply with the study restrictions.

1. Immune-compromised (known or expected immune deficiency, disease, or use of medication that may affect the immune system);
2. Close contact with infants (<2 years of age) and immune-compromised individuals, during 14 days starting from day of vaccine administration;
3. Chronic airway diseases;
4. Airway infection in the period of 14 days before first vaccine administration;
5. Active hay fever or other allergies that involve the airways;
6. Any confirmed significant allergic reactions (urticaria or anaphylaxis) against any drug, or multiple drug allergies;
7. Any anatomic or neurologic abnormality impairing the gag reflex, or associated with an increased risk of aspiration, or any abnormality significantly altering the anatomy of the nose or nasopharynx;
8. History of frequent epistaxis (nose bleeds);
9. Evidence of any other active or chronic disease (haematologic, renal, hepatic, cardiovascular, neurologic, endocrinal, gastrointestinal, oncologic, pulmonary, immunologic, or psychiatric disorders) or condition that could interfere with, or for which the treatment of might interfere with, the conduct of the study, or that would pose an unacceptable risk to the subject in the opinion of the investigator (following a detailed medical history, physical examination, vital signs (systolic and diastolic blood pressure, and body temperature) and ECG. Minor deviations from the normal range may be accepted, if judged by the Investigator to have no clinical relevance.
10. Clinically significant abnormalities, as judged by the investigator, in laboratory test results (including blood chemistry, haematology and urinalysis). In the case of uncertain or questionable results, tests performed during screening may be repeated before randomization to confirm eligibility or judged to be clinically irrelevant for healthy subjects.
11. Positive Hepatitis B surface antigen, Hepatitis B antibodies, Hepatitis C antibody, or human immunodeficiency virus antibody at screening;
12. If a woman, pregnant, or breast-feeding, or planning to become pregnant during the study or 90 days after vaccine administration;
13. Use of any medications (prescription or over-the-counter (OTC)), within 14 days of vaccine administration, or less than 5 half-lives (whichever is longer). Exceptions is paracetamol (up to 4 g/day). Other exceptions will only be made if the rationale is clearly documented and accepted by the investigator.
14. History of abuse of addictive substances (alcohol, illegal substances) or current use of more than 21 units alcohol per week, drug abuse, or regular user of sedatives, hypnotics, tranquillisers, or any other addictive agent;
15. Smoking in the 90 days preceding screening;
16. Positive test for drugs of abuse at screening or pre-dose;
17. Participation in an investigational drug or device study within 3 months prior to first dosing or more than 4 times a year;
18. Loss or donation of blood over 500 mL within three months (males) or four months (females) prior to screening or intention to donate blood or blood products during the study;
19. Any known factor, condition, or disease that might interfere with treatment compliance, study conduct or interpretation of the results.