An AE is defined as any untoward medical occurrence in a participant temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product. All AEs were assesed by the Investigateor as related or not related to the study treatment.

Safety Population: participants who received >=1 dose of study medication.

An AE is defined as any untoward medical occurrence in a participant temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product. AEs that occured during the study were evaluated by the Investigator and graded according to the Division of Acquired Immunodeficiency Syndrome (DAIDS) table for grading the severity of adult and pediatric AEs. Grade 3=severe; Grade 4=potentially life threatening.

Safety Population.

An AE is defined as any untoward medical occurrence in a participant temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product. AEs that occured during the study were evaluated by the Investigator and graded according to the DAIDS table for grading the severity of adult and pediatric AEs. Grade 3=severe; Grade 4=potentially life threatening. All AEs were assesed by the Investigateor as related or not related to the study treatment.

Safety Population.

An AE is defined as any untoward medical occurrence in a participant temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product.

Safety Population.

An AE is defined as any untoward medical occurrence in a participant temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product.

Safety Population.

Blood samples for laboratory assessments were collected at Baseline (Day [D] 1), Days 3 and 5, and on post-treatment +2 days (if hospitalized) and post-treatment +23 days. Clinical chemistry parameters included alanine aminotransferase (ALT), direct bilirubin (DB), total bilirubin (TB), and creatinine. The number of participants with values that were high (H)/normal (N)/low (L) relative to the normal range at Baseline (D 1) and D 5 for the indicated clinical chemistry parameters are summarized. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Safety Population

Blood samples for laboratory assessments were collected at Baseline (Day [D] 1), Days 3 and 5, and on post-treatment +2 days (if hospitalized) and post-treatment +23 days. Hematology parameters included hemoglobin, total neutrophils (TN), and white blood cell (WBC) count. The number of participants with values that were high (H)/normal (N)/low (L) relative to the normal range at Baseline (D 1) and D 5 for the indicated hematology parameters are summarized. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Safety Population

A toxicity was considered to be TE if it was greater than the Baseline grade, and if it had developed or increased post-Baseline in intensity (and prior to the last dose of investigational product). Clinical chemistry parameters included ALT, TB, and creatinine. Per the DAIDS table for grading the severity of adult and pediatric AEs, Grade 3=severe and Grade 4=potentially life threatening. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Safety Population

A toxicity was considered to be TE if it was greater than the Baseline grade, and if it had developed or increased post-Baseline in intensity (and prior to the last dose of investigational product). The hematology parameters included hemoglobin, TN, and WBC count. Per the DAIDS table for grading the severity of adult and pediatric AEs, Grade 3=severe and Grade 4=potentially life threatening. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Safety Population

Heart rate was measured at Baseline (Day 1); Days 2, 3, 4, 5, 6, 7, 8, 9, and 10; post-treatment +2 days, +5 days, +9 days, +16 days (assessments to be done if participant remained hospitalized), and +23 days. Heart rate was assessed once daily during inpatient or outpatient follow-up visits. Heart rate values at Baseline (Day 1) and Day 5 are summarized. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X, X in the category titles).

Safety Population

SBP and DBP were measured at Baseline (Day 1), Days 2, 3, 4, 5, 6, 7, 8, 9, and 10; post-treatment +2 days, +5 days, +9 days, +16 days (assessments to be done if participant remained hospitalized), and +23 days. SBP and DBP were assessed once daily during inpatient or outpatient follow-up visits. SBP and DBP values at Baseline (Day 1) and Day 5 are summarized. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X, X in the category titles).

Safety Population

TCPO2 is a noninvasive test that directly measures the oxygen level of tissue beneath the skin. Because oxygen is carried to tissues by blood flow in the arteries, TCPO2 is an indirect measure of blood flow. The percent (%) oxygen saturation was measured at Baseline (Day 1), Days 2, 3, 4, 5, 6, 7, 8, 9, and 10; and post-treatment +2 days, +5 days, +9 days, +16 days (assessments to be done if participant remained hospitalized), and +23 days. Oxygen saturation was assessed once daily during inpatient follow-up visits. The median oxygen saturation values at Baseline (Day 1) and Day 5 are summarized. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X, X in the category titles).

Safety Population

Respiration rate was measured at Baseline (Day 1), Days 2, 3, 4, 5, 6, 7, 8, 9, and 10; and post-treatment +2 days, +5 days, +9 days, +16 days (assessments to be done if participant remained hospitalized), and +23 days. Respiration rate was assessed once daily during inpatient or outpatient follow-up visits. The median respiration rate at Baseline (Day 1) and Day 5 is summarized. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X, X in the category titles).

Safety Population

Body temperature was recorded at Baseline (Day 1), Days 2, 3, 4, 5, 6, 7, 8, 9, and 10; and post-treatment +2 days, +5 days, +9 days, +16 days (assessments to be done if participant remained hospitalized), and +23 days. Body temperature was recorded once daily during inpatient or outpatient follow-up visits. Median body temperature at Baseline (Day 1) and Day 5 is summarized. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X, X in the category titles).

Safety Population

The number of participants with an ECG status of normal and abnormal CS or NCS, as determined by the Investigator, is reported. Normal=all ECG parameters within the accepted normal ranges. Abnormal=ECG findings outside of normal ranges. CS=ECG with a CS abnormality that meets exclusion criteria. NCS=ECG with an abnormality that is not CS nor meets exclusion criteria, per Investigator, based on reasonable standards of clinical judgment. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X in the category titles).

Safety Population

Twelve-lead ECGs were recorded for the parameters of QTcF and QTcB. The first set of pre-dose ECG values at Baseline (Day 1) and the pre-dose ECG values at Day 5 are presented. Baseline is defined as the last pre-treatment value collected. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X, X in the category titles). "NA" indicates that data are not available/analysis was not performed. Cohort 1 QTcF and QTcB minimum values of 0.0 were data entry errors that could not be addressed after Data Base Freeze.

Safety Population

Time to virologic improvement is defined as a 2-log drop in viral load or undetectable viral ribonucleic acid (RNA) as measured by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) from nasopharyngeal samples (PCR positive at Baseline). Only those participants available at the specified time points were analyzed.

ITT-E Population consisted of all participants who receiveed at least one dose of IV zanamivir.

Change from Baseline in viral load was measured from nasopharyngeal swab samples, as determined by RT-PCR (PCR positive at Baseline). Nasopharyngeal swab samples were collected at Baseline (Day 1); Day 2, Day 3, Day 4, Day 5, Day 7, and Day 10; and, only if the participants had continued symptoms and were hospitalized, post-treatment (PT) samples were collected at +2 days, +5 days, +9 days, +16 days, and +23 days. 'PT +23 days' also comprises viral load values at early study withdrawal. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X in the category titles). "NA" indicates that data are not available/analysis was not performed.

ITT-E Population

Viral susceptibility to zanamivir at Baseline and at all post-Baseline visits collectively was assessed by neuraminidase (NA) enzyme inhibition assay. The mean IC50 data are summarized by subtype (A/H1N1, A/H3N2, B) and by visit. IC50 is defined as the concentration of zanamvir required to inhibit NA activity by 50%. Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles). "NA" indicates that data are not available/analysis was not performed. Please note: pediatric data are pending and will be updated when available.

ITT-E Population

Viral RNA isolated from participants at Baseline (Day 1) and post-Baseline visits were sequenced to determine the presence of TE neuraminidase (NA) and hemagglutinin (HA) mutations resulting from selective pressure. A mutation was considered to be TE if it was not present at Baseline and was present in the last post-Baseline sample analyzed.These mutations were classified as either known to confer zanamvir resistance or novel mutations with unknown clinical significance. Please note: pediatric data are pending and will be updated when available.

ITT-E Population

Times to return to afebrile status (normal body temperature), normal respiratory status, normal heart rate, and normal systolic blood pressure were assessed. Afebrile status is defined as a temperature <=36.6 axilla, <=37.2 oral, or <=37.7 rectal, core or typanic, degrees Centigrade. A return to normal respiratory status is defined as either: (a) return to pre-morbid oxygen requirement; or (b) return to no need for supplemental oxygen; or (c) respiratory rate <=60, <=40, <=34, <=30, <=24 or <=24 breaths/minute (without supplemental oxygen) for Cohorts 1-6 respectively . A normal HR is defined as <=160, <=150, <=140, <=120, <=100 or <=100 bpm for Cohorts 1-6 respectively, and a normal SBP is defined as >=70, >=74, >=76, >=80, >=90 or >=90 mmHg for Cohorts 1-6 respectively. Only those participants available at the specified time points were analyzed (represented by n=X, X, X, X, X, X in the category titles).

ITT-E Population

Ventilation status was measured at Baseline (Day 1); Days 2, 3, 4, 5, 6, 7, 8, 9, and 10; and post-treatment +2 days, +5 days, +9 days, +16 days (assessments to be done if participant remained hospitalized), and +23 days. Ventilation status was assessed once daily during inpatient follow-up visits. The number of participants reported for machine-assisted: extracorporeal membrane oxygenation (ECMO), endotracheal mechanical ventilation, and supplemental oxygen delivery (SOD) at "any time (AT) on study" and at Baseline (Day 1) are summarized.

ITT-E Population

Due to the conditional nature of data collection post treatment, the duration of mechanical ventilation and supplemental oxygen use were not determined.

ITT-E Population

Time to return to pre-morbid functional status was assessed on a 3-point scale (bed rest, limited ambulation, or unrestricted). Only those participants available at the specified time points were analyzed.

ITT-E Population

The number of participants who died on or before Study Day 14 and Study Day 28 was summarized. Only those participants available at the specified time points were analyzed.

ITT-E Population

Sustained resolution of the following vital signs (composite) was assessed: afebrile status, normal oxygen saturation, normal respiratory status, normal HR, and normal BP. Clinical response is defined as the resolution of at least four of five vital signs within the following resolution criteria, maintained for 24 hours or hospital discharge, whichever occurred first: Temperature in degrees Centigrade (<=36.6 axilla, <=37.2 oral, <=37.7 rectal, core or tympanic); oxygen saturation (>=95%, without supplemental oxygen); respiratory status (return to pre-morbid oxygen requirement, or no need for supplemental oxygen, or respiratory rate <=60, <=40, <=34, <=30, <=24 or <=24 breaths/minute without supplemental oxygen for Cohorts 1-6 respectively); HR (<=160, <=150, <=140, <=120, <=100 or <=100 bpm for Cohorts 1-6 respectively); SBP (>=70, >=74, >=76, >=80, >=90 or >=90 mmHg for Cohorts 1-6 respectively). Only those participants available at the specified time points were analyzed.

ITT-E Population

An AE is defined as any untoward medical occurrence in a participant temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product.

ITT-E Population

Concomitant medications (prescription and non-prescription) were permitted during the course of the study at the Investigator's discretion (except for prohibited medications: during the treatment period with IV zanamivir, other influenza antiviral drugs were not permitted). The number of participants who were treated with antibiotics for influenza complications was summarized.

ITT-E Population

The duration of hospitalization (H) reflects the number of hospitalization days between the date of the first dose of investigational product and the date of discharge. ICU stay includes total duration in ICU and may include days in ICU before entry into the study. For participants with a missing discharge date who were not discharged at the end of the study, the date of discharge was imputed to the last follow-up visit (post-treatment +23 days). Only those participants available at the specified time points were analyzed (represented by n=X in the category titles).

ITT-E Population

The Cmax of zanamivir was evaluated at the end of infusion. Serial blood samples for pharmacokinetic (PK) analysis were collected if possible in conjunction with the initial dose on Day 1 (5-7 serial samples) and over a dosing interval during repeat dosing on Days 3, 4, or 5 (5 serial samples). PK data for all participants with available blood samples were analyzed. PK data for those participants who were neither on extracorporeal membrane oxygenation (ECMO) nor on continuous renal replacement therapy (CRRT), who were with CLcr >=80 mL/minutes (>=80mL/minute/1.73m^2 for cohorts 1-4) and who received an initial dose (ID) and a maintenance dose (MD) of 14 mg/kg (6 months to <6 years of age), 12 mg/kg, not to exceed 600 mg (6 to <18 years of age) or 600 mg zanamivir (>=18 years of age) (represented by n=X in the category titles) were summarized. "NA" indicates that data are not available/analysis was not performed.

PK Parameter Population: participants with one or more estimated zanamivir PK parameters

The AUC(0-tau) during the repeat dose interval and AUC(0-inf) for the initial dose were evaluated. Serial blood samples for PK analysis were collected if possible in conjunction with the initial dose on Day 1 (5-7 serial samples) and over a dosing interval during repeat dosing on Days 3, 4, or 5 (5 serial samples). PK data for all participants with available blood samples were analyzed. PK data for those participants with a CLcr >=80 mL/minutes (>=80 mL/minute/1.73m^2 for cohorts 1-4) and who received an ID and a MD of 14 mg/kg (6 months to <6 years of age), 12 mg/kg, not to exceed 600 mg (6 to <18 years of age) or 600 mg zanamivir (>=18 years of age) (represented by n=X in the category titles) were summarized. "NA" indicates that data are not available/analysis was not performed.

PK Parameter Population

The t1/2 of zanamivir was evaluated. Terminal half life is defined as the time it takes for a substance to lose half of its pharmacologic, physiologic, or radiologic activity. Serial blood samples for PK analysis were collected if possible in conjunction with the initial dose on Day 1 (5-7 serial samples) and over a dosing interval during repeat dosing on Day 3, 4, or 5 (5 serial samples). PK data for all participants with available blood samples were analyzed. PK data for those participants with a CLcr>=80 mL/minutes (>=80 mL/minute/1.73m^2 for cohorts 1-4) and who received an ID and a MD of 14 mg/kg (6 months to <6 years of age), 12 mg/kg, not to exceed 600 mg (6 to <18 years of age) or 600 mg zanamivir (>=18 years of age) (represented by n=X in the category titles) were summarized. "NA" indicates that data are not available/analysis was not performed.

PK Parameter Population

The serum clearance of zanamivir was evaluated. Clearance is defined as the volume of zanamivir per unit time eliminated from serum. Serial blood samples for PK analysis were collected if possible in conjunction with the initial dose on Day 1 (5-7 serial samples) and over a dosing interval during repeat dosing on Days 3, 4, or 5 (5 serial samples). PK data for all participants with available blood samples were analyzed. PK data for those participants with a CLcr >=80 mL/minutes (>=80 mL/minute/1.73m^2 for cohorts 1-4) and who received an ID and a MD 14 mg/kg (6 months to <6 years of age), 12 mg/kg, not to exceed 600 mg (6 to <18 years of age) or 600 mg zanamivir (>=18 years of age) (represented by n=X in the category titles) were summarized. "NA" indicates that data are not available/analysis was not performed.

PK Parameter Population

The Vd of zanamivir was evaluated. Volume of distribution is defined as the apparent volume in which zanamivir is distributed. Serial blood samples for PK analysis were collected if possible in conjunction with the initial dose on Day 1 (5-7 serial samples) and over a dosing interval during repeat dosing on Days 3, 4, or 5 (5 serial samples). PK data for all participants with available blood samples were analyzed. PK data for those participants with a CLcr >= 80 mL/minutes (>=80 mL/minute/1.73m^2 for cohorts 1-4) and who received an ID and a MD of 14 mg/kg (6 months to <6 years of age), 12 mg/kg, not to exceed 600 mg (6 to <18 years of age) or 600 mg zanamivir (>=18 years of age) (represented by n=X in the category titles) were summarized. "NA" indicates that data are not available/analysis was not performed.

PK Parameter Population