A Study to Evaluate the Safety, Tolerability and Immunogenicity of an Investigational RSV Vaccine Candidate (Ad26.RSV.preF) in Adults 18 to 50 Years of Age, and RSV-seropositive Toddlers 12 to 24 Months of Age

The study, designed to assess the safety and tolerability of two doses given one month apart
of Ad26.RSV.preF, an investigational RSV vaccine candidate based on a Ad26 vector expressing
the RSV F protein, will be conducted in a double blinded manner. The study will be divided in
two sequential cohorts: cohort 0 (18-50 year-old adults) and cohort 1 (12-24 month-old RSV
seropositive toddlers). The vaccine safety will be monitored by reporting solicited and
unsolicited adverse events (AEs) and all serious adverse events (SAEs). The data will be
reviewed by an independent data monitoring committee (IDMC) to assess safety data and to
ensure the continuing safety of the participants enrolled in this study. The safety will be
monitored throughout the study.

Inclusion Criteria:

Adults Participants:

- Participant must be in good health, without significant medical illness, on the basis
of physical examination, medical history, and vital signs measurement

- Participant must be healthy on the basis of clinical laboratory tests performed at
screening. If the results of the laboratory screening tests are outside the local
laboratory normal reference ranges and additionally within the limits of toxicity
Grade 1 according to the United stated (US) Food and Drug Administration (FDA)
toxicity tables, the participant may be included only if the investigator judges the
abnormalities or deviations from normal to be not clinically significant and
appropriate and reasonable for the population under study. This determination must be
recorded in the participant's source documents and initialed by the investigator

- All women of childbearing potential must have a negative highly sensitive serum
beta-human chorionic gonadotropin (Beta-hCG) pregnancy test at screening and a
negative urine Beta-hCG pregnancy test immediately prior to each study vaccine
administration

Pediatric Participants:

- Participant is the product of a normal term pregnancy greater than and equal to (>=)
37 weeks, with a minimum birth weight of 2.5 kilogram (kg)

- Participants must be in good health without any significant medical illness on the
basis of physical examination, medical history, and vital signs performed at screening

Exclusion Criteria:

Adults Participants:

- Participant has acute illness (this does not include minor illnesses such as diarrhea)
or temperature >=38.0 ºC (degree celsius)/100.4 °F (fahrenheit) within 24 hours prior
to the first dose of study vaccine

- Participant has a history of an underlying clinically significant acute or chronic
medical condition or physical examination findings for which, in the opinion of the
investigator, participation would not be in the best interest of the participant
(example, compromise the well-being) or that could prevent, limit, or confound the
protocol-specified assessments

- Participant has history of malignancy within 5 years before screening (exceptions are
squamous and basal cell carcinomas of the skin and carcinoma in situ of the cervix, or
malignancy, which is considered cured with minimal risk of recurrence)

Pediatric Participants:

- Participant's weight is below 10th percentile according to World Health Organization
(WHO) pediatric growth and weight charts

- Participant has any clinically significant acute or chronic medical condition that, in
the opinion of the investigator, would preclude participation: example, history of
seizure disorders, bleeding/clotting disorder, autoimmune disease, active malignancy,
systemic infections, congenital heart disease, history of any pulmonary condition
requiring medication, atopy, reactive airway disease, medically-confirmed wheezing,
bronchoconstriction or treatment with a beta2 agonist, cystic fibrosis,
bronchopulmonary dysplasia, chronic pulmonary disease, medically-confirmed apnea,
hospitalization for respiratory illness, or mechanical ventilation for respiratory
illness