The clinical status at Day 7 was based on a 6-point ordinal scale:

1. Death
2. In ICU
3. Non-ICU hospitalization, requiring supplemental oxygen (O2)
4. Non-ICU hospitalization, not requiring supplemental oxygen
5. Not hospitalized, but unable to resume normal activities
6. Not hospitalized with full resumption of normal activities A higher score corresponds to a better health outcome

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment (with available data).

The clinical status at Day 1 was based on a 6-point ordinal scale:

1. Death
2. In ICU
3. Non-ICU hospitalization, requiring supplemental oxygen (O2)
4. Non-ICU hospitalization, not requiring supplemental oxygen
5. Not hospitalized, but unable to resume normal activities
6. Not hospitalized with full resumption of normal activities A higher score corresponds to a better health outcome

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

The clinical status at Day 2 was based on a 6-point ordinal scale:

1. Death
2. In ICU
3. Non-ICU hospitalization, requiring supplemental oxygen (O2)
4. Non-ICU hospitalization, not requiring supplemental oxygen
5. Not hospitalized, but unable to resume normal activities
6. Not hospitalized with full resumption of normal activities A higher score corresponds to a better health outcome

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

The clinical status at Day 3 was based on a 6-point ordinal scale:

1. Death
2. In ICU
3. Non-ICU hospitalization, requiring supplemental oxygen (O2)
4. Non-ICU hospitalization, not requiring supplemental oxygen
5. Not hospitalized, but unable to resume normal activities
6. Not hospitalized with full resumption of normal activities A higher score corresponds to a better health outcome

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

The clinical status at Day 14 was based on a 6-point ordinal scale:

1. Death
2. In ICU
3. Non-ICU hospitalization, requiring supplemental oxygen (O2)
4. Non-ICU hospitalization, not requiring supplemental oxygen
5. Not hospitalized, but unable to resume normal activities
6. Not hospitalized with full resumption of normal activities A higher score corresponds to a better health outcome

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

The clinical status at Day 28 was based on a 6-point ordinal scale:

1. Death
2. In ICU
3. Non-ICU hospitalization, requiring supplemental oxygen (O2)
4. Non-ICU hospitalization, not requiring supplemental oxygen
5. Not hospitalized, but unable to resume normal activities
6. Not hospitalized with full resumption of normal activities A higher score corresponds to a better health outcome

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

Duration (in days) of initial hospitalization, restricted to duration between randomization and last visit

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

Number of deaths during study follow-up

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

Number of deaths in the hospital during initial hospitalization

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

Two categories were considered for the composite of mortality and hospitalization:

Dead or hospitalized Alive and not hospitalized

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

The National Early Warning (NEW) score was only measured for the adult participants.

The range of the NEW score is from 0 to 20, with lower values representing a better outcome.

Baseline is defined as the Day 0. Change was defined as the value at Day 3 or Day 7 minus the value at baseline.

Modified intent-to-treat adult population: subgroup of randomized adult participants who received any study treatment

The Pediatric Early Warning (PEW) score was only measured for the pediatric participants.

The range is from 0 to 26, with lower values representing a better outcome. Baseline is defined as the Day 0. Change was defined as the value at Day 3 or Day 7 minus the value at baseline.

Modified intent-to-treat pediatric population: subgroup of randomized pediatric participants who received any study treatment

Duration (in days) of total supplemental oxygen use among those participants who required new or increased oxygen at randomization.

The duration is restricted to duration between randomization and last visit.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants who required new or increased oxygen at randomization.

Incidence of new oxygen use during the study among those participants who did not require oxygen at randomization

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants who did not require oxygen at randomization.

Duration (in days) of ICU stay among those participants who were in ICU at randomization.

The duration is restricted to duration between randomization and last visit.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants who were in the ICU at randomization.

Incidence of new ICU admission during the study among those participants who were not in ICU at randomization

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants who were not in the ICU at randomization.

Duration (in days) of mechanical ventilation use among those participants who were on mechanical ventilation at randomization.

The duration is restricted to duration between randomization and last visit.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants who were on mechanical ventilation at randomization.

Incidence of new mechanical ventilation use during the study among those participants who were not on mechanical ventilation at randomization

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants who were not on mechanical ventilation at randomization.

Duration (in days) of ARDS use among those participants with ARDS at randomization.

The duration is restricted to duration between randomization and last visit.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants with ARDS at randomization.

Incidence of new ARDS during the study among those participants without ARDS at randomization

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants without ARDS at randomization.

Duration (in days) of ECMO use among those participants on ECMO at randomization.

The duration is restricted to duration between randomization and last visit.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants who were on ECMO at randomization.

Incidence of new ECMO use during the study among those participants not on ECMO at randomization

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment, further subset to those participants who were not on ECMO at randomization.

The Sequential Organ Failure Assessment (SOFA) score was only measured for the adult participants.

The range is from 0 to 24, with lower values representing a better outcome. Baseline is defined as the Day 0. Change was defined as the value at Day 3 or Day 7 minus the value at baseline.

Modified intent-to-treat adult population: subgroup of randomized adult participants who received any study treatment.

The Pediatric Logistic Organ Dysfunction (PELOD) score was only measured for the pediatric participants.

The range is from 0 to 71, with lower values representing a better outcome. Baseline is defined as the Day 0. Change was defined as the value at Day 3 or Day 7 minus the value at baseline.

Modified intent-to-treat pediatric population: subgroup of randomized pediatric participants who received any study treatment

Disposition at discharge after initial hospitalization was categorized as follows:

Death, Ongoing at 28 days, Chronic nursing facility, Rehabilitation, Home with home health care, Home without assistance.

The number of deaths at discharge after initial hospitalization do not necessarily match the overall number of deaths.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

Detectable influenza virus at Day 3 in oropharyngeal samples

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment. This group was further subset wo those with available OP sample results at Day 3.

Hemagglutination inhibition assay (HAI) titers as measured by serial dilutions at Days 1, 3, 7 for A/H1N1. HAI for A/H1N1 was tested in all influenza seasons while the study was ongoing.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

Hemagglutination inhibition assay (HAI) titers as measured by serial dilutions at Days 1, 3, 7 for A/HongKong/4801/2014 H3N2. HAI for A/HongKong/4801/2014 H3N2 was tested in all influenza seasons while the study was ongoing.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment

Number of participants with reported grade 3 and 4 adverse events (AEs) throughout the study duration. In cases where participants had multiple reports of grade 3 and 4 AEs, they were only counted once.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment.

Number of participants with reported serious adverse events (SAEs) throughout the study duration.

Modified intent-to-treat population: subgroup of randomized participants who received any study treatment.