Plasma concentrations of EDP-938 were assessed at the designated time points.

Pharmacokinetic (PK) Population: Included all participants in Part 1 who received one full dose of study drug and had samples with quantifiable plasma levels to allow for estimation of PK parameters. Per protocol, data were analyzed per age group and dose received.

TEAEs were defined as any event, side effect, or untoward medical occurrence in a participant enrolled in a clinical study whether or not it was considered to have a causal relationship to the study drug and first occurred or worsened during the post-baseline phase compared to baseline. Clinically significant changes from baseline in vital signs and clinical laboratory results were reported as TEAEs.

Safety Population: Included all participants in Part 1 who received any dose (including partial doses) of any study drug. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

Daily change from baseline in RSV shedding was defined as the daily change from baseline in RSV ribonucleic acid (RNA) viral load and was measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) from nasal swabs. The model included treatment group (EDP-938, placebo) and Day (3, 5, 9, and 14) as fixed effect, associated baseline, and treatment group by Day interaction term as factors. An unstructured covariance matrix was imposed. The Satterthwaite approximation is used to estimate the denominator degrees of freedom.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

Daily change from baseline in RSV shedding was defined as the daily change from baseline in RSV RNA viral load and was measured using RT-qPCR from nasal swabs. The model included treatment group (EDP-938, placebo) and Day (3, 5, 9, and 14) as fixed effect, associated baseline, and treatment group by Day interaction term as factors. An unstructured covariance matrix was imposed.The Satterthwaite approximation is used to estimate the denominator degrees of freedom.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

The RSV RNA viral load was measured using RT-qPCR from nasal swabs. The AUC was calculated using the trapezoid rule. The AUC was calculated based on all available assessments collected on Days 1, 3, 5, 9 and 14 and the actual date/time of each assessment was used for the calculation.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

The RSV RNA viral load was measured using RT-qPCR from nasal swabs. The AUC was calculated using the trapezoid rule. The AUC was calculated based on all available assessments collected on Days 1, 3, 5, 9 and 14 and the actual date/time of each assessment was used for the calculation. The model included treatment group (EDP-938, placebo) and Day (3, 5, 9, and 14) as fixed effect, associated baseline, and treatment group by day interaction term as factors. An unstructured covariance matrix was imposed. The Satterthwaite approximation was used to estimate the denominator degrees of freedom.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

Daily change from baseline in RSV shedding in nasal swab samples was defined as the absolute daily change from baseline in RSV RNA viral load and measured using RT-qPCR from nasal swabs.

Efficacy Population: Included all participants in Part 1 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

The RSV RNA viral load was measured using RT-qPCR from nasal swabs.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Included only participants with detectable viral load at baseline and non-missing viral load assessment at the respective visit and was used as a denominator in the percentage population.

The RSV RNA viral load was measured using RT-qPCR from nasal swabs.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Included only participants with detectable viral load at baseline and non-missing viral load assessment at the respective visit and was used as a denominator in the percentage population.

Time to RSV RNA viral load being undetectable was calculated as: first date of RSV RNA viral load target not detected (TND) after which no further samples had detectable RSV RNA viral load - date of first dose.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

Time to RSV RNA viral load being undetectable was calculated as: first date of RSV RNA viral load TND after which no further samples had detectable RSV RNA viral load - date of first dose.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

TEAEs were defined as any event, side effect, or untoward medical occurrence in a participant enrolled in a clinical study whether or not it was considered to have a causal relationship to the study drug and first occurred or worsened during the post-baseline phase compared to baseline. Clinically significant changes from baseline in vital signs and clinical laboratory results were reported as TEAEs.

Safety Population: Included all participants in Part 2 who received any dose (including partial doses) of any study drug. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

TEAEs were defined as any event, side effect, or untoward medical occurrence in a participant enrolled in a clinical study whether or not it was considered to have a causal relationship to the study drug and first occurred or worsened during the post-baseline phase compared to baseline. Clinically significant changes from baseline in vital signs and clinical laboratory results were reported as TEAEs.

Safety Population: Included all participants who received any dose (including partial doses) of any study drug. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

Plasma concentrations of EDP-938 were assessed at the designated time points.

PK Population: Included all participants in Part 2 who received one full dose of study drug and had samples with quantifiable plasma levels to allow for estimation of PK parameters. Per protocol, data were analyzed per age group and dose received.

Plasma concentrations of EDP-938 were assessed at the designated time points.

PK Population: Included all participants who received one full dose of study drug and had samples with quantifiable plasma levels to allow for estimation of PK parameters. Per protocol, data were analyzed per age group and dose received.

Time to first discharge for participants who were hospitalized at randomization was calculated as: date/time of first discharge - date/time of first dose with conversion to days. For participants with continuous hospitalization, the last date of discharge from the continuous hospitalization was used.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Only participants who were hospitalized at randomization were included. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

Time to first discharge for participants who were hospitalized at randomization was calculated as: date/time of first discharge - date/time of first dose with conversion to days. For participants with continuous hospitalization, the last date of discharge from the continuous hospitalization was used.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Only participants who were hospitalized at randomization were included. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose.

For participants were were hospitalized at randomization, time to use of oxygen for hospitalization participants who were not receiving oxygen at the time they received the first dose of study drug was calculated as: first date/time of receiving oxygen - date/time of first dose of study drug with conversion to days.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. As there were no participants in Part 2 in both arms who were hospitalized at randomization who were not receiving oxygen at the time they received the first dose of study drug, no data were collected for this outcome measure.

For participants were were hospitalized at randomization, time to use of oxygen for hospitalization participants who were not receiving oxygen at the time they received the first dose of study drug was calculated as: first date/time of receiving oxygen - date/time of first dose of study drug with conversion to days.

Efficacy Population. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only hospitalized participants who were not receiving oxygen at the time they received the first dose of study drug were included. In the Placebo arm, there were no hospitalized participants who were not receiving oxygen at the time they received the first dose of study drug.

The numerator in the percentage calculation was defined by the number of participants who developed a new requirement for oxygen supplementation or new increase in oxygen requirements after the first dose of study drug, based on the response of "yes" to the "Is this an increase of oxygen supplementation compared to previous use?" question on the Oxygen Supplementation case report form (CRF). The 95% confidence interval was reported using the Clopper Pearson confidence interval methods.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only participants who were hospitalized at randomization and/or during the study were included.

The numerator in the percentage calculation was defined by the number of participants who developed a new requirement for oxygen supplementation or new increase in oxygen requirements after the first dose of study drug, based on the response of "yes" to the "Is this an increase of oxygen supplementation compared to previous use?" question on the Oxygen Supplementation CRF. The 95% confidence interval was reported using the Clopper Pearson confidence interval methods.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only participants who were hospitalized at randomization and/or during the study were included.

Time to mechanical ventilation for participants who were hospitalized at randomization was calculated as: first date/time of mechanical ventilation - date/time of first dose of study drug with conversion to days. Participants who were on mechanical ventilation before their first dose of study drug were excluded from the analysis.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. As only participants who were hospitalized at baseline and experienced mechanical ventilation were included, no data were collected for this outcome measure.

Time to mechanical ventilation for participants who were hospitalized at randomization was calculated as: first date/time of mechanical ventilation - date/time of first dose of study drug with conversion to days. Participants who were on mechanical ventilation before their first dose of study drug were excluded from the analysis.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. As only participants who were hospitalized at baseline and experienced mechanical ventilation after their first dose of study drug were included, no data were collected for this outcome measure.

The numerator in the percentage calculation was defined by the number of participants who developed a new requirement for mechanical ventilation after the first dose of study drug. Participants on mechanical ventilation prior to the first dose of study drug were excluded from analysis. The 95% confidence interval was reported using the Clopper Pearson confidence interval methods.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only hospitalized participants who were not on mechanical ventilation prior to the first dose of study drug were included.

The numerator in the percentage calculation was defined by the number of participants who developed a new requirement for mechanical ventilation after the first dose of study drug. Participants on mechanical ventilation prior to the first dose of study drug were excluded from analysis. The 95% confidence interval was reported using the Clopper Pearson confidence interval methods.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only hospitalized participants who were not on mechanical ventilation prior to the first dose of study drug were included.

The percentage of hospitalized participants who died during the study included deaths from any cause. The 95% confidence interval was reported using the Clopper Pearson confidence interval methods.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only participants who were hospitalized at randomization and/or during the study were included.

The percentage of hospitalized participants who died during the study included deaths from any cause. The 95% confidence interval was reported using the Clopper Pearson confidence interval methods.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only participants who were hospitalized at randomization and/or during the study were included.

Time to hospitalization for initial outpatients who are not hospitalized at randomization but subsequently hospitalized was calculated as: first date/time of hospitalization - date/time of first dose with conversion to days.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. As only participants who were not hospitalized at randomization but subsequently hospitalized were included, no data were collected for this outcome measure.

Time to hospitalization for initial outpatients who are not hospitalized at randomization but subsequently hospitalized was calculated as: first date/time of hospitalization - date/time of first dose with conversion to days.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. As only participants who were not hospitalized at randomization but subsequently hospitalized were included, no data were collected for this outcome measure.

Participants who were hospitalized at randomization were excluded from the analysis. The 95% confidence interval was reported using the Clopper Pearson confidence interval methods.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only participants who were not hospitalized at randomization were included.

Participants who were hospitalized at randomization were excluded from the analysis. The 95% confidence interval was reported using the Clopper Pearson confidence interval methods.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only participants who were not hospitalized at randomization were included.

Resolution of symptoms was defined as the first of 2 consecutive timepoints where each of the seven symptoms assessed by the Parent/Caregiver Respiratory Syncytial Virus (RSV) Foundation (ReSVinet) score was 0 (not present) or 1 (mild). Time to resolution of symptoms for outpatients who were not hospitalized was calculated as: first date/time of resolution of symptoms - date/time of first dose with conversion to days. Participants who did not achieve resolution and had not been followed through the Day 14 visit or completed the Day 14 questionnaire were censored at Day 14.

During the study, the parent(s)/caregiver(s) assessed the severity of RSV-related signs and symptoms. The ReSVinet assessed 7 symptoms, with each symptom being rated from 0 (not present) to 3 (severe), apart from fever which was scored from 0-2. The full range was 0 to 20 with higher scores representing more severe disease.

Efficacy Population: Included all participants in Part 2 who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only participants who were not hospitalized were included.

Resolution of symptoms was defined as the first of 2 consecutive timepoints where each of the seven symptoms assessed by the Parent/Caregiver ReSVinet score was 0 (not present) or 1 (mild). Time to resolution of symptoms for outpatients who were not hospitalized was calculated as: first date/time of resolution of symptoms - date/time of first dose with conversion to days. Participants who did not achieve resolution and had not been followed through the Day 14 visit or completed the Day 14 questionnaire were censored at Day 14.

During the study, the parent(s)/caregiver(s) assessed the severity of RSV-related signs and symptoms. The ReSVinet assessed 7 symptoms, with each symptom being rated from 0 (not present) to 3 (severe), apart from fever which was scored from 0-2. The full range was 0 to 20 with higher scores representing more severe disease.

Efficacy Population: Included all participants who received one full dose of study drug and had at least one evaluable measurement while on treatment. Per the protocol, analyses were planned to be grouped by EDP-938 and placebo, rather than by dose. Only participants who were not hospitalized were included.