A Two-Part Infant Study for Early Diagnosis of Respiratory Syncytial Virus (RSV) and Evaluation of JNJ-53718678 in RSV Acute Respiratory Tract Disease

A Two-Part Study With a Birth Cohort (Observational Stage) for Early Diagnosis of Respiratory Syncytial Virus (RSV), Followed by an Optional Phase 2a, Randomized, Double-blind, Placebo-controlled Study (Interventional Stage) to Evaluate the Antiviral Activity, Clinical Outcomes, Safety, Tolerability, and Pharmacokinetics of JNJ-53718678 in Infants With Acute Respiratory Tract Infection Due to RSV

The purpose of this two-part designed study is to assess in the setting of a planned early interception of pediatric RSV disease, early viral and disease kinetics (observational stage) and the antiviral effects of an Respiratory Syncytial Virus (RSV) fusion inhibitor, JNJ-53718678 (interventional stage). In the observational stage the infant is closely monitored for early symptoms by the parent(s)/caregiver(s) and thus may be brought in for diagnosis earlier than in the typical setting.

Inclusion Criteria:

Part 1: Observational Stage

• The infant is less than or equal to (<=) 4 months of age at enrollment and asymptomatic for acute respiratory illness (ARI)-like symptoms requiring medical intervention at the time of consent to participate in the study
• At least 1 parent/caregiver must be able to use the respiratory syncytial virus (RSV) mobile application (App) at home via his/her own Android/iOS electronic device (compatible with RSV mobile App)
• The participant must have been assessed per local public health practice and considered not to have Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection

Part 2: Interventional Stage

• The infant is 28 days and if prematurely born infant (that is [i.e.], less than [<] 37 weeks and 0 days of gestation at birth) is at least 3 months postnatal age
• The participant has been diagnosed with RSV infection using a rapid molecular-based diagnostic assay
• The participant weighs more than 2.4 kilogram (kg)
• The participant has an acute respiratory illness as evaluated by the investigator
• Except for the RSV-related illness, the participant must be medically stable in case of allowed co-morbid conditions
• The participant must have been assessed per local public health practice and considered not to have SARS-CoV-2 infection during this respiratory infection

Exclusion Criteria:

Part 1: Observational Stage

• The participant has any physical abnormality which limits the ability to collect regular nasal specimens
• The participant is receiving chronic home oxygen therapy at enrollment (applicable to both parts)

Part 2: Interventional Stage

• The participant is <3 months postnatal age at screening and was born prematurely (i.e., <37 weeks and 0 days of gestation) or if the participant weights <2.4 kg
• The participant has a QT interval with Fridericia's correction (QTcF) greater than (>) 450 milliseconds per the machine read (mean of triplicate) parameter result confirmed by repeat triplicate Electrocardiogram (ECG) recording during screening
• The participant is considered by the investigator to be immunocompromised, whether due to underlying medical condition or medical therapy
• The participant has had any of: a) Confirmed SARS-CoV-2 infection (test positive) during the four weeks prior to randomization, or b) Close contact with a person with Coronavirus Disease 2019 (COVID-19) (test confirmed or suspected SARS-CoV-2 infection) within 14 days prior to randomization