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.
Participants will not receive any intervention in observational phase of this study. Participant's respiratory symptoms will be captured by RSV mobile application installed in participant's caregiver/parent mobile phone.
Participants in each Age Group (1,2,3) will receive matching placebo (volume placebo to match the calculated volume of the JNJ-53718678 dose) orally twice daily for 7 days.
JNJ-53718678 will be administered to Age Group 1 twice daily for 7 days.
JNJ-53718678 will be administered to Age Group 2 twice daily for 7 days.
JNJ-53718678 will be administered to Age Group 3 twice daily for 7 days.
San Miguel de Tucumán, Argentina