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

RSV viral load AUC was determined from immediately prior to first dose of JNJ-53718678 through Day 5. The RSV viral load was measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay in mid-turbinate nasal swab specimens.

Time frame: Baseline (Day 1) up to Day 5

Population: Intent-To-Treat-infected (ITT-i) analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of greater than or equal to (\>=) 1 log10 copies per milliliter (mL) above the lower limit of quantification (LLOQ) of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set were performed as randomized.

Change from baseline in clinician (for concepts: activity level, sleep disturbance, breathing problems, retractions, tachypnea, feeding problem, cough, nasal secretions, wheezing, dehydration) PRESORS scores was reported. PRESORS is a questionnaire recording presence and severity of signs and symptoms of RSV disease. PRESORS score consisted of 10-items, each item score ranges from 0 to 3. A summary score was derived (mean of the item scores) which also ranges from 0 to 3. The higher the score, the worse the symptom.

Time frame: Baseline, Day 3, 5, 8, 14, 21

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had centrally confirmed RSV viral load of \>=1 log10 copies per mL above LLOQ of RSV RT-qPCR assay at baseline. Analyses on ITT-i set were performed as randomized. Here 'N' (number of participants analyzed), included all participants who were evaluable for this outcome measure; 'n' (number analyzed) included all participants who were analyzed at specified timepoints for specific category.

PRESORS is a questionnaire recording presence and severity of signs and symptoms of RSV disease. PRESORS score consisted of 12-items, each item score ranges from 0 to 3. A summary score was derived (mean of the item scores) which also ranges from 0 to 3. The higher the score, the worse the symptom.

Time frame: Baseline, Day 3, 5, 8, 14, 21

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>=1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set were performed as randomized. Here 'N' (number of participants analyzed), included all participants who were evaluable for this outcome measure. Here 'n' (number analyzed) included all participants who were analyzed at specified timepoints.

Change from baseline in RSV viral load over time was measured by qRT-PCR in the nasal swab specimens collected at the clinic visits and at home.

Time frame: Baseline, Days 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, and 21

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>= 1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set were performed as randomized. Here, 'n' (number analyzed) included all participants who were analyzed at specified timepoints.

Percentage of participants who require (re)hospitalization during treatment and follow-up were reported.

Time frame: Up to Day 31

Population: The Safety set (SAF) included all participants who received at least 1 dose of study drug, and were analyzed as treated, regardless of the randomized treatment group assigned. Where 'analyzed as treated' is defined as: Placebo: if only placebo doses received, and JNJ-53718678: if at least one dose of the active study drug received.

Percentage of participants with abnormal chemistry laboratory findings (alanine aminotransferase \[ALT; Grade 1 and 4\], aspartate aminotransferase \[AST; Grade 1\], and Hyperkalemia \[Grade 1 and 2\]) were reported based on Division of Microbiology and Infectious Diseases (DMID) toxicity grading scale. DMID toxicity grades ranges from 1 to 4. Grade 1 = mild: transient or mild discomfort (\<48 hours); no medical intervention/therapy required. Grade 2 = moderate: mild to moderate limitation in activity - some assistance may be needed; no or minimal medical intervention/therapy required. Grade 3 = severe: marked limitation in activity, some assistance usually required; medical intervention/therapy required, hospitalizations possible. Grade 4 = life-threatening or death: Extreme limitation in activity, significant assistance required; significant medical intervention/therapy required, hospitalization or hospice care probable.

Time frame: Up to Day 31

Population: The SAF included all participants who received at least 1 dose of study drug, and were analyzed as treated, regardless of the randomized treatment group assigned. Where 'analyzed as treated' is defined as: Placebo: if only placebo doses received, and JNJ-53718678: if at least one dose of the active study drug received. Here 'n' (number analyzed) included all participants who were analyzed at specified categories.

Percentage of participants with abnormal ECGs findings were reported. Parameters for abnormal ECG findings were QT interval corrected for heart rate (QTc) according to Bazett's formula (QTcB) Interval (\[450 milliseconds {ms}, 480 ms\], \[480 ms, 500 ms\], and \[more than 500 ms\]), QTc according to Fridericia's formula (QTcF) Interval (\[450 ms, 480 ms\], \[480 ms, 500 ms\], and \[more than 500 ms\]), change from baseline for QTcB Interval (\[30; 60\] ms, and greater than \[\>\] 60 ms), and for QTcF Interval (\[30; 60\] ms, and \>60 ms).

Time frame: Up to Day 31

Population: The SAF included all participants who received at least 1 dose of study drug, and were analyzed as treated, regardless of the randomized treatment group assigned. Where 'analyzed as treated' is defined as: Placebo: if only placebo doses received, and JNJ-53718678: if at least one dose of the active study drug received. Here 'N' (number of participants analyzed), included all participants who were evaluable for this outcome measure.

Percentage of participants with abnormal urinalysis (Hematuria- Grade 1) laboratory finding was reported based on DMID toxicity grading scale. DMID toxicity grades ranges from 1 to 4. Grade 1 = mild: transient or mild discomfort (\<48 hours); no medical intervention/therapy required. Grade 2 = moderate: mild to moderate limitation in activity - some assistance may be needed; no or minimal medical intervention/therapy required. Grade 3 = severe: marked limitation in activity, some assistance usually required; medical intervention/therapy required, hospitalizations possible. Grade 4 = life-threatening or death: Extreme limitation in activity, significant assistance required; significant medical intervention/therapy required, hospitalization or hospice care probable.

Time frame: Up to Day 31

Population: The SAF included all participants who received at least 1 dose of study drug, and were analyzed as treated, regardless of the randomized treatment group assigned. Where 'analyzed as treated' is defined as: Placebo: if only placebo doses received, and JNJ-53718678: if at least one dose of the active study drug received. Here 'N' (number of participants analyzed), included all participants who were evaluable for this outcome measure.

An adverse event is any untoward medical event that occurs in a participant administered an investigational product, and it does not necessarily indicate only events with clear causal relationship with the relevant investigational product.

Time frame: Up to Day 31

Population: The SAF included all participants who received at least 1 dose of study drug, and were analyzed as treated, regardless of the randomized treatment group assigned. Where 'analyzed as treated' is defined as: Placebo: if only placebo doses received, and JNJ-53718678: if at least one dose of the active study drug received.

Percentage of participants with undetectable RSV viral load at each time point throughout the study were reported.

Time frame: Baseline, Days 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 21

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>=1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set was performed as randomized. Here 'n' (number analyzed) included all participants who were analyzed at specified timepoints.

Percentage of participants with vital signs (systolic blood pressure \[SBP\], diastolic blood pressure \[DBP\], pulse rate, respiratory rate, body temperature and peripheral capillary oxygen saturation \[SpO2\]) abnormalities (abnormally low \[ABL\] and abnormally high \[ABH\]) were reported.

Time frame: Up to Day 31

Population: The SAF included all participants who received at least 1 dose of study drug, and were analyzed as treated, regardless of the randomized treatment group assigned. Where 'analyzed as treated' is defined as: Placebo: if only placebo doses received, and JNJ-53718678: if at least one dose of the active study drug received. Here 'n' (number analyzed) included all participants who were analyzed for specified categories.

Percentage of participants with worsening or improvement of RSV disease based on general questions on overall health was reported. Improvement is defined improvement of RSV symptoms reported as very much improved or much improved based on response to question 'Would you say the child's RSV symptoms have improved, are about the same or are worse than when the child entered the study'.

Time frame: On Days 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>=1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set were performed as randomized. Here 'n' (number analyzed) included all participants who were analyzed at specified timepoints.

No data was collected for pharmacokinetic (PK) analysis due to small sample size. Hence, no results are reported.

Time frame: Day 1 and Day 3

Population: No data was collected for PK analysis due to small sample size. Hence, no results are reported.

RSV viral load AUC was determined by qRT-PCR assay in mid-turbinate nasal swab specimens.

Time frame: Baseline through Days 3, 8, and 14

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>=1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set was performed as randomized. Here 'n' (number analyzed) included all participants who were analyzed at specified timepoints. At Day 14, data was not collected due to low sample size.

RSV viral load actual values over time was measured by qRT-PCR in the nasal swab specimens collected at the clinic visits and at home.

Time frame: Baseline, Days 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, and 21

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>= 1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set were performed as randomized. Here 'n' (number analyzed) included all participants who were analyzed at specified timepoints.

The severity of signs and symptoms of RSV infection (breathing problems, retractions, tachypnea, breathing sounds, cough, tachycardia, nasal secretions, sleep disturbance, crying, illness behavior, feeding problems, and dehydration) were assessed by the PRESORS. PRESORS is a questionnaire by parent(s)/caregiver(s) recording presence and severity of signs and symptoms of RSV disease. PRESORS score consisted of 12-items, each score ranges from 0 to 3. A summary score was derived (mean of the item scores) which also ranges from 0 to 3. The higher the score, the worse the symptom.

Time frame: Baseline, Days 3, 5, 8, 14, and 21

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>=1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set was performed as randomized. Here 'n' (number analyzed) included all participants who were analyzed at specified timepoints.

Time to improvement based on general questions on overall health was reported. Time from first dose of study drug until first time status of improvement of RSV symptoms reported as very much improved or much improved based on response to question 'Would you say the child's RSV symptoms have improved, are about the same or are worse than when the child entered the study'.

Time frame: Up to 21 days

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>=1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set was performed as randomized.

Time to resolution from first dose of study drug until the first time of resolution of all RSV Symptoms (breathing problems, retractions, tachypnea, breathing sounds, cough, tachycardia, nasal secretions, sleep disturbance, crying, illness behavior, feeding problems, and dehydration). Resolution occurs when all symptoms from the caregiver reported outcomes (ObsRO) are scored as none or mild (score of 0 or 1, respectively) for at least 24 hours.

Time frame: Up to 21 days

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had a centrally confirmed RSV viral load of \>=1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set were performed as randomized.

Time to return to pre-RSV health as rated by the parent(s)/caregiver(s) was evaluated. It is the time from first dose of study drug until the time to return to pre-RSV disease level.

Time frame: Up to 21 days

Population: Data was not collected due to low number of participants. Hence, no results are reported.

Time to undetectable RSV viral load is defined as the time in hours from initiation of study treatment until the first post-baseline time point at which the virus is confirmed undetectable. A confirmed undetectable sample is defined as the first of at least two consecutive samples that are undetectable. The last obtained sample for a participant, if undetectable, is considered confirmed.

Time frame: Up to 21 days

Population: ITT-i analysis set included all randomized participants who received at least one dose of study drug and who had centrally confirmed RSV viral load of \>=1 log10 copies per mL above the LLOQ of the RSV RT-qPCR assay at baseline. Analyses on the ITT-i set was performed as randomized.