Area under the RSV VL-time curve (AUC) was determined as log10 copies*hour per milliliter (Log10 copies*hr/mL) by quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay of mid turbine nasal swabs.

The intent-to-treat-infected (ITT-i) population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Area under the RSV VL-time curve (AUC) was determined as Log10 copies*hr/mL by qRT-PCR assay of mid turbine nasal swabs.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Area under the RSV VL-time curve (AUC) was determined as Log10 copies*hr/mL by qRT-PCR assay of mid turbine nasal swabs.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Area under the RSV VL-time curve (AUC) was determined as Log10 copies*hr/mL by qRT-PCR assay of mid turbine nasal swabs.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Change from baseline in RSV viral load at Day 3 was measured as Log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Change from baseline in RSV viral load at Day 5 was measured as Log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Change from baseline in RSV viral load at Day 8 was measured as Log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Change from baseline in RSV viral load at Day 14 was measured as Log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Change from baseline in RSV viral load oat Day 21 was measured as Log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

RSV viral load was measured as log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

RSV viral load was measured as log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

RSV viral load was measured as log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

RSV viral load was measured as log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

RSV viral load was measured as log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

RSV viral load was measured as log10 copies/mL by qRT-PCR assay in the mid-turbinate nasal swab specimens.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

The time to undetectable nasal RSV RNA viral load was defined as the time in days from initiation of study treatment until first post-baseline time point at which RSV RNA was undetectable and after which time there were no more detectable virus assessments.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection.

Percentage of participants with undetectable RSV viral load at Day 3 were reported.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Percentage of participants with undetectable RSV viral load at Day 5 were reported.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Percentage of participants with undetectable RSV viral load at Day 8 were reported.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Percentage of participants with undetectable RSV viral load at Day 14 were reported.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Percentage of participants with undetectable RSV viral load at Day 21 were reported.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of 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.

The safety analysis set included all participants who received at least 1 dose of study agent, analyzed as treated.

Number of participants with worst treatment-emergent laboratory abnormalities (serum chemistry, hematology and urinalyses) were reported based on DMID toxicity grading scale. DMID toxicity grade categorized as Grade 1=mild(mild discomfort (< 48 hours); no medical intervention/therapy required), Grade 2= moderate (Moderate Mild to moderate limitation in activity - some assistance may be needed; no or minimal medical intervention/therapy required), Grade 3= severe (severe Marked limitation in activity, some assistance usually required; medical intervention/therapy required, hospitalizations possible), and Grade 4=life threatening (extreme limitation in activity, significant assistance required; significant medical intervention/therapy required, hospitalization or hospice care probable).

The safety analysis set included all participants who received at least 1 dose of study agent, analyzed as treated. Here 'N' (number of participants analyzed) signifies number of participants who were valuable for this outcome measure. Here, "n (number analysed)" is defined as number of participants analyzed for specified category.

Number of participants with worst treatment emergent vital sign abnormalities (including Systolic blood pressure [SBP] and diastolic blood pressure [DBP]) as abnormally low, mild increased, moderate increased and severe increased were reported. SBP: Abnormally low- Less than or equal to (<=) 50 mmHg, Grade 1 (mild)- 90 mmHg - < 100 mmHg, Grade 2 (moderate)- greater than or equal to (>=)100 mmHg to < 110 mmHg, Grade 3 (severe)- >=110 mmHg; DBP: Abnormally low- <=90 mmHg, Grade 1 (mild)- 140 mmHg - < 160 mmHg, Grade 2 (moderate)- >=160 mmHg to < 180 mmHg, Grade 3 (severe)- >=180 mmHg.

The safety analysis set included all participants who received at least 1 dose of study agent, analyzed as treated. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

The number of participants with worst TE ECG abnormalities were reported. The ECG variables that were analyzed included heart rate, PR interval, QRS interval, QT interval, and corrected QT (QTc) interval. Parameters for abnormal ECG findings were QT interval corrected for heart rate (QTc) according to Bazett's formula (QTcB or Borderline Prolonged QTcB) Interval ([450 milliseconds {ms}, 480 ms], [480 ms, 500 ms], and [more than 500 ms]), QTc according to Fridericia's formula (QTcF or Borderline Prolonged QTcB) Interval ([450 ms, 480 ms], [480 ms, 500 ms], and [more than 500 ms]).

The safety analysis set included all participants who received at least 1 dose of study agent, analyzed as treated. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure. Here, 'n' (number analyzed) signifies number of participants who were analyzed for specified categories.

Peripheral capillary oxygen saturation was measured by the investigator over time.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Change from baseline in peripheral capillary oxygen saturation levels was calculated by the investigator.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Pulse rate was measured by the investigator over time.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints.

Change from baseline in pulse rate was calculated and reported by the investigator.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Respiratory rate was measured by the investigator over time.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Change from baseline in respiratory rate was calculated and reported by the investigator.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Body temperature was measured over time. Participants were provided a thermometer and asked to record body temperature in the electronic device.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints.

Change from baseline in body temperature was calculated and reported. Participants were provided a thermometer and asked to record body temperature in the electronic device.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

AUC (0-24) is defined as area under the plasma concentration-time curve from time point 0 hours until 24 hours post dose.

Pharmacokinetic (PK) analysis set included all participants who received JNJ-53718678 and for whom at least one PK concentration was reported. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

The severity of signs and symptoms of RSV infection was assessed using the RI-PRO questionnaire. The RI-PRO questionnaire is 32-item questionnaire. It summarizes severity of 6 symptom domains: nose (4 items), throat (3 items), eyes (3 items), chest/respiratory (7 items), gastrointestinal (4 items), and body/systemic (11 items). Each RI-PRO domain score ranges from 0 (symptom free) to 4 (very severe symptoms). Domain scores were calculated as the arithmetic mean of the scores for items within the domain.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints for specified categories.

Duration of signs and symptoms of RSV infection was assessed by the time to resolution of all RSV symptoms from RI-PRO questionnaire. Resolution was defined as a score of 'Not at all/symptom-free' (score=0) or 'A little bit' (score=1) for at least 24 hours. The RI-PRO questionnaire is a 32-item questionnaire. It summarizes severity of 6 symptom domains: nose (4 items), throat (3 items), eyes (3 items), chest/respiratory (7 items), gastrointestinal (4 items) and body/systemic (11 items). Each RI-PRO score ranges from 0 (symptom-free) to 4 (very severe symptoms).

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Time to resolution of key RSV symptoms (congested or stuffy nose, sore or painful throat, trouble breathing, chest tightness, coughing, coughed up mucus or phlegm, weak or tired) as assessed by RI-PRO questionnaire was reported. Resolution of RSV symptoms was defined as a score of 'Not at all/symptom free' (score = 0) or 'A little bit' (score = 1) for at least 24 hours for symptoms of the RI-PRO questionnaire. The RI-PRO questionnaire is 32-item questionnaire. It summarizes severity of 6 symptom domains: nose (4 items), throat (3 items), eyes (3 items), chest/respiratory (7 items), gastrointestinal (4 items), and body/systemic (11 items). Each RI-PRO score ranges from 0 (symptom-free) to 4 (very severe symptoms).

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Time from the first dose of study drug until the time to return to usual activity/health was determined. Return to usual activity/health when the response is 'Yes' on RI-PRO additional question 7 ('Have you returned to your usual activity/health today?') for at least 24 hours.

The ITT-i population consisted of all randomized participants who received at least 1 dose of study drug and who had a central lab-confirmed RSV infection.

Ctrough is the trough plasma concentration of JNJ-53718678 estimated by population PK model.

PK analysis set included all participants who received JNJ-53718678 and for whom at least one PK concentration was reported. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.

Cmax is the maximum plasma concentration of JNJ-53718678 estimated by population PK model.

PK analysis set included all participants who received JNJ-53718678 and for whom at least one PK concentration was reported. Here, 'n' (number analyzed) signifies number of participants who were analyzed at specified timepoints. Here 'N' (number of participants analyzed) signifies number of participants who were evaluable for this outcome measure.