Oxygenation Index is defined as Mean Airway Pressure multiplied by (Fraction of Inspired Oxygen[FiO2]) x (100)/(Partial Pressure of Oxygen[PaO2]). It is a measure of efficiency of oxygen utilization in the body, with lower values indicating better oxygenation. OI values can range from 0 to 1000, with values below 25 generally associated with more favorable clinical outcomes. OI at Day 7 was derived according to estimand definition. If a participant died before or at Day 7 and OI was missing, an unfavorable value was imputed. If a participant was extubated at Day 7 and OI was not evaluable, a favorable value was imputed. In all other cases, OI at Day 7 was considered missing. Baseline was defined as last measurement collected prior to investigational medicinal product intake. Change from baseline was defined as post-baseline assessment minus baseline value. Adjusted means and 95% confidence interval from an ANOVA model with multiple imputation (MI) for missing data have been presented.

Randomized Set.

Ventilator free days (VFDs) through Day 28 were defined as the number of days from the first IMP intake during which the participant was alive and free of invasive mechanical ventilation. Participants who died before or at Day 28 were assigned a value of 0 ventilator-free days, in accordance with the estimand definition. Adjusted means and 95% confidence interval from an ANOVA model with MI for missing data have been presented.

Randomized Set.

Oxygenation Index (OI) is defined as Mean Airway Pressure multiplied by (FiO2) x (100) / (PaO2). It is a measure of the efficiency of oxygen utilization in the body, with lower values indicating better oxygenation. OI values can range from 0 to 1000, with values below 25 generally associated with more favorable clinical outcomes. OI at Day 7 was derived according to the estimand definition. If a participant died before or at Day 7 and OI was missing, an unfavorable value was imputed. If a participant was extubated at Day 7 and OI was not evaluable, a favorable value was imputed. In all other cases, OI at Day 7 was considered missing. For Day 4, no imputation or adjusted means were applied; only observed data from participants with available measurements were used. Baseline was defined as the last measurement collected prior to IMP intake. Change from baseline was defined as the difference between the value at each post-baseline assessment and the baseline value.

Full Analysis Set population comprises of all randomized participants who received at least one dose of the investigational product. Only those participants with data available at specified timepoints have been presented.

Acute Lung Injury (ALI) Score is a composite 4-point scoring system validated by the National Heart, Lung, and Blood Institute (NHLBI) acute respiratory distress syndrome (ARDS) Network that considers PaO2/FiO2, the level of positive end-expiratory pressure (PEEP), lung/respiratory compliance [plateau airway pressure minus PEEP/Tidal Volume (TV)], and the extent of pulmonary infiltrates on the chest radiograph. Each criterion was scored from 0-4 based on the severity of the condition. The final score was calculated by dividing the total score by the number of criteria used. A score of 0 indicates no lung injury, a score between 0.1 to 2.5 indicates mild to moderate lung injury and a score of >2.5 indicates severe lung injury (ARDS). Baseline was defined as the last measurement collected prior to IMP intake, regardless of the visit at which it was obtained. Change from baseline was defined as the difference between the value at each post-baseline assessment and the baseline value.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

The Sequential Organ Failure Assessment (SOFA) Score is a mortality prediction score based on the degree of dysfunction of six organ systems (respiratory, cardiovascular, hepatic, coagulation, renal and neurological systems). The score ranges for each system organ classes range from 0 to 4. SOFA score was calculated every 24 hours using (for each organ system) the worst variable recorded within the same 24 hours. The best possible score corresponds to 0 whereas the worst score corresponds to 24. Baseline was defined as the last measurement collected prior to IMP intake, regardless of the visit at which it was obtained. Change from baseline was defined as the difference between the value at each post-baseline assessment and the baseline value.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

The Ventilatory Ratio (VR) is a simple, non-invasive bedside index used to monitor the efficiency of carbon dioxide (CO2) clearance in mechanically ventilated participants, particularly those with ARDS.

VR = [minute ventilation (ml/min) × PaCO2 (mm Hg)] / [predicted body weight × 100 (ml/min) × 37.5 (mm Hg)] VR is a unitless ratio, and a value approximating 1 would represent normal ventilating lungs. An elevated value of VR would represent either increased pulmonary dead space, increased VCO2 or both. Baseline was defined as the last measurement collected prior to IMP intake, regardless of the visit at which it was obtained. Change from baseline was defined as the difference between the value at each post-baseline assessment and the baseline value.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Extracorporeal Membrane Oxygenation (ECMO) is an advanced form of temporary life support used for participants with life-threatening heart or lung failure that has not responded to conventional treatments. It functions as a modified heart-lung bypass machine, circulating blood outside the body to add oxygen and remove carbon dioxide before returning it to the participants. Use of ECMO between first investigational medicinal product intake and Day 14 was counted.

Full Analysis Set.

Use of vasoactive medication is defined as the percentage of participants who received ≥1 vasoactive medication at any time from first IMP intake (Day 1) up to and including Day 14 (inclusive window), divided by the number of participants in the analysis population. Use of Vasoactive Medications is collected in "Ventilation - Specific Information" CRF Daily assessments through extubation. An event is recorded as "Yes" if vasoactive medication use is reported at any daily assessment performed between the date/time of first IMP intake (Day 1) and Day 14 (Day 1 + 13 days), inclusive. If no use is reported during this period, the event is recorded as "No" provided the last available assessment occurs on or after Day 12 (allowing a ±2-day window for the Day 14 visit). The event is recorded as missing if the last available assessment occurs before Day 12.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Radiographic Assessment of Lung Edema (RALE) score is a validated, semi-quantitative tool for quantifying pulmonary edema and ARDS severity using chest X-rays (CXR). It is calculated by dividing the lung fields on the chest radiograph into four quadrants. Each quadrant was assigned a number, and the extent of alveolar opacities (the consolidation score, from 0 to 4) and density of alveolar opacities (the density score, from 1 to 3) was determined. If the consolidation score was 0, the density score was 0. The final RALE score was the sum of the product of the consolidation and density score for each quadrant. Thus, the final RALE score ranged from minimum 0 to maximum 48. Higher RALE scores indicate more severe edema and poorer outcomes. Baseline was defined as the last measurement collected prior to IMP intake, regardless of the visit at which it was obtained. Change from baseline was defined as the difference between the value at each post-baseline assessment and the baseline value.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Continuous Positive Airway Pressure (CPAP) is defined as use of pressure support ventilation equal to 5 cmH2O with PEEP equal to 5 cmH2O for 2 hours. Each qualifying CPAP trial recorded in the Ventilation Specific Information CRF is counted as one weaning attempt. By Day 28: An event is recorded as "Yes" if at least one CPAP weaning attempt (>0) is reported between Day 1 (first IMP intake) and Day 28 (Day 1 + 27 days). The event is "No" if all available assessments during this period are present and equal to 0; otherwise, the event is missing. By Hospital Discharge: An event is recorded as "Yes" if at least one CPAP weaning attempt (>0) is reported between Day 1 and hospital discharge. The event is "No" if all available assessments during this period are present and equal to 0; otherwise, the event is missing. Hospital discharge date is obtained from EOS or, if missing, from the Hospital Discharge visit date; if unavailable, hospitalization is assumed ongoing.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Intensive Care Unit (ICU) free days were defined as number of calendar days from first IMP intake during which a participant was alive and not hospitalized in an ICU. ICU-free days at Day 28 were calculated as 28 minus total number of ICU days up to Day 28, with negative values set to 0. Participants who died on or before Day 28 were assigned 0 ICU-free days. If a participant was discharged before Day 28 and died after discharge but before Day 28, ICU-free days at Day 28 equaled ICU-free days at discharge. Endpoint was set to missing if participant was alive but followed for fewer than 26 days or if required data were missing. ICU-free days at hospital discharge were calculated as (discharge date - first IMP intake date + 1) minus total ICU days up to discharge, with negative values set to 0. Participants who died during hospitalization were assigned 0 ICU-free days. If discharge did not occur and death occurred after Day 28, ICU-free days at discharge equaled ICU-free days at Day 28.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Hospital-free days are a participant-centered metric defining the number of days a participant stays alive outside an acute-care hospital. If the participant was alive at Day 28 (last available day ≥26), hospital-free days were calculated as 28 minus total hospital days up to Day 28. If the participant died on or before Day 28, hospital-free days were set to 0.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Percentage of participants who underwent a tracheostomy between Day 1 and Day 28 or hospital discharge, has been presented. The event is recorded as "Yes" if a tracheostomy occurred during this period, "No" if no procedure occurred and the visit/discharge date is available and missing if both the procedure date and visit/discharge date are unavailable.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

An LTAC is a Long Term Acute Care Hospital, a facility that specializes in the treatment of participants with serious medical conditions, including patients with ongoing needs for mechanical ventilation, but who no longer require intensive care or extensive diagnostic procedures. The participants in LTAC are transferred there directly from the intensive care unit because they require more care than they can receive in a rehabilitation center, skilled care facility or at home.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Percentage of death by Day 28 and Day 60 has been reported. The event is recorded as "Yes" if death occurred within the period, "No" if the participant was alive with last available assessment at or beyond Day 28 or Day 60.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

A participant was considered discharged alive by Day 28 if hospital discharge occurred on or before Day 28, regardless of vital status after discharge. Participants were considered not discharged alive by Day 28 if they died without a recorded discharge date, were discharged after Day 28, had a missing discharge date with sufficient follow-up (last available day ≥26), or had a discharge date equal to the date of death. The endpoint was set to missing if the discharge date was missing and the participant was alive but followed for fewer than 26 days. Percentage of participants discharged from hospital by Day 28 has been presented.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Plasma biomarker levels for Interleukin -6 (IL-6), IL-8 and plasma Tumor Necrosis Factor Receptor 1 (TNFr-1) were measured using validated laboratory methods. Baseline was defined as the last measurement collected prior to IMP intake, regardless of the visit at which it was obtained. Change from baseline was calculated as the post-baseline plasma concentration minus the baseline concentration.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

Plasma biomarker levels of plasminogen activator inhibitor-1 (PAI-1), intercellular adhesion molecule-1 (ICAM-1), and receptor for advanced glycation end products (RAGE) were measured using validated laboratory methods. Baseline was defined as the last measurement collected prior to IMP intake, regardless of the visit at which it was obtained. Change from baseline was calculated as the post-baseline plasma concentration minus the baseline concentration.

Full Analysis Set. Only those participants with data available at specified timepoints have been presented.

An Adverse Event (AE) is any untoward medical occurrence in a participant, which does not necessarily have a causal relationship with the trial intervention. A TEAE is defined as any untoward medical occurrence that begins or worsens in intensity or frequency after the initiation of a treatment (e.g., drug, device, or procedure) in a clinical study. A Serious TEAE is defined as any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization.

Safety Analysis consisted of all randomized participants who received at least one dose of the investigational product.