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

An adverse event (AE) is any untoward medical occurrence in a clinical study participant administered a medicinal (investigational or non-investigational) product. An AE does not necessarily have a causal relationship with the treatment. An AE can, therefore, be any unfavorable and unintended sign (including an abnormal finding), symptom, or disease temporally associated with the use of a medicinal (investigational or non-investigational) product, whether or not related to that medicinal (investigational or non-investigational) product. All AEs reported during treatment or follow-up were considered emergent and were included in the analysis.

The number of participants with clinically significant physical examination (respiratory system, nose, ear, throat, facial and neck lymph nodes, and skin examination) abnormalities that emerged after treatment initiation was reported.

The number of participants with emergent clinically relevant vital signs (temperature, pulse rate, respiratory rate, diastolic blood pressure, systolic blood pressure, oxygen saturation) abnormalities that emerged after treatment initiation reported. An abnormality was considered emergent in a particular phase if it is worse than baseline. If baseline is missing, the abnormality is always considered as emergent. A shift from 'abnormally low' at baseline to 'abnormally high' post baseline (or vice versa) was also emergent.

The number of participants with ECG (QT, and QTc intervals) abnormalities reported.

Number of participants with Laboratory (hematology, serum chemistry, and urinalysis) abnormalities reported based on DMID toxicity grading scale. DMID toxicity grades ranges from 1 to 4. Grade 0 is normal and not meeting the criteria of Grade 1-4. Hb: Grade 1: for 22-35 days old- 9.5-10.5 gram per deciliter (g/dL); for 36-60 days old- 8.5-9.4 g/dL; for 61-90 days old- 9.0-9.9 g/dL; Hb: Grade 2: for 22-35 days old- 8.0-9.4 g/dL, for 36-60 days old- 7.0-8.4 g/dL; for 61-90 days old- 7.0-8.9 g/dL. ALT: Grade 1- 1.1 - <2.0*Upper limit of normal (ULN); Creatinine: Grade 2- 1.8-2.4 milligram per deciliter (mg/dL); Hyperkalemia: Grade 1- 3.0-3-5 milliequivalents per Liter (mEq/L); ANC: Grade 1: for 7-60 days old- 1200-1800/ millimeter cube(mm^3); for 61-90 days old- 750-1200/mm^3; ANC: Grade 3: for 7-60 days old- 500-899/mm^3, for 61-90 days old- 250-399/mm^3; ANC: Grade 4- for 7-60 days old <500/mm^3, for 61-90 days old- <250/mm^3; Platelets: Grade 3: 25000 - 49999/mm^3.

Cmax is the maximum observed plasma concentration of JNJ-63549109 (Metabolite of Lumicitabine).

AUC is the area under the plasma concentration-time curve of JNJ-63549109 (Metabolite of Lumicitabine).

C(trough) is the plasma concentration before dosing or at the end of the dosing interval of any dose other than the first dose in a multiple dosing regimen of JNJ-63549109 (Metabolite of Lumicitabine).

C12h is the predicted concentration of JNJ-63549109 at 12 hours Postdose. C12h is a model-based prediction. It was determined using a population pharmacokinetic (PK) model and based on the individual model predicted concentration-time profiles.

Length of hospital stay is defined as the time from hospitalization to actual hospital discharge.

Number of participants who were admitted to the ICU was reported.

In the event that a participant required ICU, the duration for how long the participant remained in the ICU was reported.

The number of participants who required supplemental oxygen above pre-RSV infection status was reported.

The number of participants who required non-invasive mechanical ventilation support (that is, continuous positive airway pressure) above pre-RSV infection status was reported.

The number of participants who required invasive mechanical ventilation support (for example, endotracheal-mechanical ventilation or mechanical ventilation via tracheostomy) above pre-RSV infection status was reported.

Duration of supplemental oxygen above pre-RSV infection status was assessed.

Duration of non-invasive mechanical ventilation support (that is, continuous positive airway pressure) to deliver oxygen above pre-RSV infection status was measured.

Duration of invasive mechanical ventilation support (for example, endotracheal-mechanical ventilation or mechanical ventilation via tracheostomy) to deliver oxygen above pre-RSV infection status was measured.

Time to no longer requiring supplemental oxygen above pre-RSV infection status was reported.

Time to clinical stability was defined as the time at which the following criteria are all met: normalization of blood oxygen level (return to baseline, by pulse oximetry) without the requirement of supplemental oxygen beyond baseline level, normalization of oral feeding, normalization of respiratory rate, and normalization of heart rate.

Time from initiation of study treatment until SpO2 >=93% on room air among participants who were not on supplemental oxygen prior to the onset of respiratory symptoms was reported.

Time for the respiratory rate to return to pre-RSV infection status was measured.

Time for SpO2 to return to pre-RSV infection status was measured.

Time for body temperature to return to pre-RSV infection status was measured.

Number of participants with acute otitis media was reported.

Duration of signs and symptoms of RSV infection was assessed.

The severity of signs and symptoms of RSV infection were assessed by the PRESORS. PRESORS Score consisted of 5-items, each score ranges from 0 to 3 and the total score was analyzed by summing up the individual score ranging from 0 (minimum; best) to 15 (maximum; worse).

RSV viral load over time was measured by qRT-PCR in the mid-turbinate nasal swab specimens.

Peak viral load was measured by qRT-PCR in the mid-turbinate nasal swab specimens.

Time to peak viral load was reported.

Percentage of participants with decline in viral load during treatment as measured by qRT-PCR was reported.

Time to RSV RNA being undetectable (the time from initiation of study treatment until the time at which it is observed that the virus is undetectable in an assessment and after which time no virus positive assessment follows) was assessed as measured by qRT-PCR.

Percentage of participants with the undetectable viral load was reported.

AUC of RSV RNA viral load was measured in mid-turbinate nasal swabs and in the endotracheal sample.

AUC of RSV RNA viral load was measured in midturbinate nasal swabs and in endotracheal samples.

AUC of RSV viral load was measured in midturbinate nasal swabs and in endotracheal samples.

Number of participants with emergent postbaseline changes in the RSV polymerase L-gene and other regions of the RSV genome compared with baseline sequences were reported.

Acceptability and Palatability of lumicitabine formulation was assessed by clinician eCOA questionnaire ranging from score 0 (minimum; best) to 8 (maximum; worse).