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

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