A Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of Adenovirus Serotype 26 Based Respiratory Syncytial Virus Pre-fusion (Ad26.RSV.Pre-F) Vaccine in RSV-Seronegative Toddlers 12 to 24 Months of Age

A Randomized, Controlled, Observer-blind, Phase 1/2a Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of Ad26.RSV.preF in RSV-seronegative Toddlers 12 to 24 Months of Age

The purpose of this study is to assess the safety and reactogenicity of an intramuscular regimen of 3 doses of 2.5*10^10 viral particles (vp) of adenovirus serotype 26 based respiratory syncytial virus pre-fusion protein (Ad26.RSV.preF) vaccine in RSV-seronegative toddlers aged 12 to 24 months.

RSV is considered the most important cause of serious acute respiratory illness in children under 5 years of age. Ad26.RSV.preF (JNJ-64400141) investigational vaccine is a replication-incompetent serotype 26 adenoviral vector (Ad26) containing a deoxyribonucleic acid (DNA) transgene that encodes for the F protein derived from the respiratory syncytial virus (RSV) A2 strain stabilized in the pre-fusion conformation (Ad26.RSV.preF). The study will evaluate whether Ad26.RSV.preF is safe, well-tolerated, and immunogenic in RSV-seronegative toddlers. The study will have 3 phases: a screening phase (up to 6 weeks before the first dose), a vaccination phase (34 weeks), and a safety follow-up phase through 2 RSV seasons after the first dose. RSV infection will be monitored by active and passive surveillance. The total duration of the study will be approximately 26 months.

Inclusion Criteria:

• Participant who is seronegative for respiratory syncytial virus (RSV) within 42 days prior to dosing
• Participant is the product of a normal term pregnancy greater than or equal to (>=)37 weeks, with a minimum birth weight of 2.5 kilogram (kg)
• Participant must be in good health without any significant medical illness on the basis of physical examination, medical history, and vital signs performed at screening
• Participant has received all routine immunizations appropriate for his or her age according to local guidelines
• Each participant's parent(s)/legal guardian(s) must have access to a consistent means of contact either by telephone contact or email/computer

Exclusion Criteria:

• Participant's weight is below tenth percentile according to World Health Organization (WHO) pediatric growth and weight charts
• Participant has any clinically significant acute or chronic medical condition (for 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 beta 2 agonist, cystic fibrosis, bronchopulmonary dysplasia, chronic pulmonary disease, medically-confirmed apnea, hospitalization for respiratory illness, or mechanical ventilation for respiratory illness) that, in the opinion of the investigator, would preclude participation
• Participant is in receipt of, or planning to receive, live attenuated vaccine (for example, measles, mumps and rubella [MMR] or varicella, but excluding rotavirus vaccine) within 28 days of each study vaccination (that is, before and after); other vaccines (for example, influenza, pertussis, polio or rotavirus) should be given at least 14 days before or 14 days after each study vaccination
• Participant has known or suspected immunodeficiency, such as known human immunodeficiency virus (HIV) infection
• Participant has a known allergy to vaccines or vaccine components (including any of the constituents of the study vaccine), or history of anaphylaxis or other serious adverse reactions to vaccines or vaccine components (including any of the constituents of the study vaccine). Participants with egg allergies can be enrolled