A Study to Evaluate the Efficacy and Safety of Pimodivir in Combination With the Standard-of-Care Treatment in Adolescent, Adult, and Elderly Non-Hospitalized Participants With Influenza A Infection Who Are at Risk of Developing Complications

This double-blind (neither researchers nor participants know what treatment participant is
receiving) study will evaluate efficacy/safety of pimodivir in combination with SOC treatment
versus placebo in combination with SOC treatment in adolescent (13 to 17 years), adult (18 to
65 years), and elderly (greater than [>] 65 but less than or equal to [<=] 85 years)
non-hospitalized participants with influenza A infection who are at risk of developing
complications. The study will be conducted in 3 phases: screening phase, double-blind
treatment period (5 days), a post treatment follow-up period (23 days). Study evaluations
include efficacy, clinical and virological outcomes, pharmacokinetics (PK),
PK/pharmacodynamics, biomarkers, safety and tolerability. The duration of participation in
the study for each participant is 28 days.

Inclusion Criteria:

- Present to the clinic with symptoms suggestive of a diagnosis of acute influenza and
have at least 1 respiratory symptom and at least 1 systemic symptom, both scored as at
least "moderate" if the symptom did not pre-exist before influenza onset, or scored
worse than usual if the symptom pre-existed as determined by subject's ratings on
Module 1 of the Flu-iiQ and the Pre-existing Symptom Questionnaire in the ePRO device.
Symptoms must include the following by category: a) Respiratory symptoms: cough, sore
throat, nasal congestion b) Systemic symptoms: headache, body aches or pain,
feverishness, fatigue

- Tested positive for influenza A infection after the onset of symptoms, using a rapid
influenza diagnostic test (RIDT) or, if available, a polymerase chain reaction
(PCR)-based or other rapid molecular diagnostic assay

- Not be in need of hospitalized medical care at screening. Emergency room or hospital
observation status for an anticipated duration of less than (<)24 hours is not
considered hospitalization as long as a determination of the need for hospitalization
has not been made

- Enrollment and initiation of study drug treatment less than or equal to (<=)72 hours
after onset of influenza symptoms

- Participants 13 to 65 years of age, inclusive must also have at least 1 of the
following: a) Cardiovascular or cerebrovascular disease (including congenital heart
disease, chronic heart failure, coronary artery disease, or stroke; excluding isolated
hypertension); b) Chronic lung disease (for example, asthma, chronic obstructive lung
disease [COPD] or cystic fibrosis); c) Weakened immune system due to disease or
medication (for example, participants with human immunodeficiency virus [HIV], cancer,
or chronic liver or kidney disease [presence of kidney damage for >3 months, defined
by structural or functional abnormalities of the kidney, with or without decreased GFR
manifested by: pathological abnormalities; OR markers of kidney damage, including
abnormalities in the composition of the blood or urine or abnormalities in imaging
tests], or participants taking chronic systemic steroids)

Exclusion Criteria:

- Received more than (>)1 dose of influenza antiviral medication (for example,
oseltamivir [OST] or zanamivir), or any dose of ribavirin within 2 weeks, prior to
first study drug intake, or received intravenous (IV) peramivir >1 day prior to
screening

- Unstable angina pectoris or myocardial infarction within 30 days prior to screening
(inclusive)

- Presence of clinically significant heart arrhythmias, uncontrolled, unstable atrial
arrhythmia, or sustained ventricular arrhythmia, or risk factors for Torsade de
Pointes syndrome

- Known severe hepatic impairment (Child Pugh C cirrhosis) or chronic hepatitis C
infection undergoing hepatitis C antiviral therapy

- Severely immunocompromised in the opinion of the investigator (for example, known
cluster of differentiation 4 plus [CD4+] count <200 cells per cubic millimeter
[cells/mm^3], absolute neutrophil count <750/mm^3, first course of chemotherapy
completed within 2 weeks prior to screening, history of stem cell transplant within 1
year prior to screening, history of a lung transplant)