A Study to Evaluate the Antiviral Activity, Clinical Outcomes, Safety, Tolerability, and Pharmacokinetics of Orally Administered Lumicitabine (JNJ-64041575) Regimens in Hospitalized Infants and Children Aged 28 Days to 36 Months Infected With Respiratory Syncytial Virus

RSV is a leading cause of lower respiratory tract disease in infants. Most infants and
children who get RSV recover fully after 1-2 weeks, but RSV infection can sometimes worsen
and may lead to hospitalization and admission into an intensive care unit. The main purpose
of this study is to learn how well the study drug (lumicitabine, also known as JNJ-64041575
or ALS-008176) works, how the human body handles the study drug, which dose of the study drug
is effective for treatment of RSV infection in infants/children and how safe it is compared
to a placebo (placebo looks just like lumicitabine [given in same way] but has no effect
against RSV). Approximately up to 180 participants aged between 28 days to 36 months and
hospitalized with RSV infection will take part in this world-wide study.

Inclusion Criteria:

- Participants hospitalized (or in emergency room [ER]) at the time of randomization and
unlikely to be discharged for the first 24 hours after randomization

- Participants diagnosed with respiratory syncytial virus (RSV) infection using a
polymerase chain reaction (PCR)-based molecular diagnostic assay, with or without
co-infection with another respiratory pathogen (respiratory virus or bacteria)

- Participants who have an acute respiratory illness with signs and symptoms consistent
with a viral infection (for example, fever, cough, nasal congestion, runny nose, sore
throat, myalgia, lethargy, shortness of breath, or wheezing) with onset less than or
equal to <=5 days from the anticipated time of randomization. Onset of symptoms is
defined as the first time (within 1 hour) the parent(s)/caregiver(s) becomes aware of
respiratory or systemic symptoms of RSV infection

- With the exception of the symptoms related to the RSV infection or defined comorbid
condition for severe RSV disease (prematurity at birth [participant's gestational age
was less than {<}37 weeks; for infants <1 year old at randomization], bronchopulmonary
dysplasia, congenital heart disease, other congenital diseases, Down syndrome,
neuromuscular impairment, or cystic fibrosis), participant must be medically stable on
the basis of physical examination, medical history, vital signs/peripheral capillary
oxygen saturation (SpO2), and electrocardiogram (ECG) performed at screening. If there
are abnormalities, they must be consistent with the underlying condition in the study
population and/or the RSV infection. This determination must be recorded in the
participant's source documents and initialed by the investigator. Participants with
comorbidities will be allowed to be enrolled once the Independent Data Monitoring
Committee (IDMC) has reviewed the pharmacokinetic (PK) and safety data of the highest
dose that will be used in this study and once the IDMC has recommended opening
recruitment to this group. Sites will be notified when the restriction is lifted

- The participant's estimated glomerular filtration rate (eGFR) is not below the lower
limit of normal for the participant's age

Exclusion Criteria:

- Participants who are not expected to survive for more than 48 hours

- Participants who have had major thoracic or abdominal surgery in the 6 weeks prior to
randomization

- Participants who have a known or suspected immunodeficiency (except immunoglobulin A
[IgA] deficiency), such as a known human immunodeficiency virus infection

- Participants being treated with extracorporeal membrane oxygenation

- Participant receiving chronic oxygen therapy at home prior to admission

- Participants who have a poorly functioning gastrointestinal tract (that is, unable to
absorb drugs or nutrition via enteral route)