A Study to Evaluate the Safety and Efficacy of CD388 for Prevention of Influenza

Inclusion Criteria:

1. Must be 12 years of age or older at the time of signing the informed consent.

2. Written informed consent and any locally required authorization (e.g., HealthInsurance Portability and Accountability Act [HIPAA] in the US) obtained from theparticipant before performing any protocol-related procedures, including screeningevaluations. For participants under the legal age of consent as defined by localregulations, the parent(s) or legal guardian(s) may be required to give their signedwritten informed consent and participants may sign an assent form as specified bylocal law.

3. Has negative rapid antigen tests for influenza and severe acute respiratory syndromecoronavirus 2 (SARS-CoV-2) prior to dosing at Day 1.

4. Weight is ≥ 40 kilograms (kg) at screening.

5. Body Mass Index (BMI; calculated as weight in kg divided by height in meters [m]squared)) is ≥ 18 kg/m^2 at screening.

6. In the opinion of the Investigator, must be able to comply with the requirements ofthe protocol and be able to read, understand, and complete questionnaires in theelectronic diary (eDiary), work with smartphones/tablets/computers (if applicable,with assistance by a caregiver, surrogate, or legally authorized representative),and be willing and able to adhere to the prohibitions and restrictions specified inthis protocol. If an appropriate language version is not available for the eDiaryassessments, the participant should not be enrolled.

7. Must be assessed by the Investigator as medically stable and not requiringsignificant change in maintenance therapy and has not been hospitalized forworsening disease or any significant medical event during the 2 months beforescreening

8. Must agree to the following contraception requirements: a. Females of childbearing potential must use a highly effective, preferablyuser-independent, method of contraception (failure rate of less than 1 percent peryear when used consistently and correctly) from ≥2 weeks prior to randomization andagree to remain on a highly effective method from Day 1 until 32 weeks after studyintervention administration, the end of relevant systemic exposure. Note: A woman isconsidered of childbearing potential (i.e., fertile) following menarche and untilbecoming postmenopausal, unless permanently sterile. Permanent sterilization methodsinclude hysterectomy, bilateral salpingectomy, and bilateral oophorectomy. Apostmenopausal state is defined as no menses for 12 months without an alternativemedical cause. A high follicle stimulating hormone (FSH) level in the postmenopausalrange may be used to confirm a postmenopausal state in women not using hormonalcontraception or hormonal replacement therapy. However, in the absence of 12 monthsof amenorrhea, a single FSH measurement is insufficient. Note: Contraceptive (birth control) use by participants should be consistent withlocal regulations regarding the acceptable methods of contraception for thoseparticipating in clinical studies.

9. Must agree not to donate blood or blood products from Day 1 until 32 weeks afterstudy intervention administration.

10. Must be willing to provide verifiable identification, has means to be contacted, andis able to contact the Investigator/study site and communicate reliably duringparticipation in the study.

11. In addition to inclusion criteria 1 through 10 above, participants are eligible tobe included in Primary Stratum A of the study (higher risk non-immunocompromised)only if one or more of the following criteria apply:

12. Has a history of pulmonary disease; specifically:

• Chronic obstructive pulmonary disease (COPD), including chronic bronchitisand emphysema, graded as follows using the Global Initiative for ChronicObstructive Lung Disease (GOLD) Categories A, B, and E (ABE) (i.e., GOLDABE) assessment tool:
• Gold Grade 2 (moderate) or Grade 3 (severe) with followingexacerbation history, within 1 year of screening
• At least 2 moderate exacerbations (i.e., not leading tohospitalization), or
• At least 1 exacerbation leading to hospitalization OR
• Gold Grade 4 regardless of exacerbation history
• Bronchiectasis, cystic fibrosis, interstitial lung disease,pneumoconiosis, or past or active bronchopulmonary dysplasia.

2. Has moderate to severe asthma, as defined by the Global Initiative for Asthma (GINA) Treatment Steps 3-5.

3. Has existing cardiac disease; specifically:

• Congenital heart disease
• Congestive heart failure New York Heart Association (NYHA) Class II-IV
• Coronary artery disease requiring regular medication and/or follow-up forischemic heart disease (i.e., participants who, through interventionalprocedure[s] and/or active medical treatment, have attained an establishedstate of chronic stability of a duration of no less than 6 months)
• Hypertension with cardiac complications (NOTE: Hypertension alone withoutcardiac complications will be excluded). Acceptable cardiac complicationsof hypertension include, but are not limited to, heart failure, cardiacarrhythmias (e.g., atrial fibrillation), ischemic heart disease, coronaryartery disease, enlarged left heart, metabolic syndrome, left ventricularhypertrophy, systolic or diastolic myocardial dysfunction, angina, andmyocardial infarction.

4. Has insulin-dependent diabetes.

5. Has moderate renal impairment (Stage 3 Chronic Kidney Disease [CKD], equivalentto an estimated glomerular filtration rate [eGFR] 30 to 59 milliliter perminute [mL/min] per 1.73 m^2 as calculated by the Chronic Kidney DiseaseEpidemiology Collaboration [CKD-EPI] equation for adults or the Chronic KidneyDisease in Children under 25 [CKiD U25] equation for adolescents) with orwithout micro-macroproteinuria and within 3 months prior to screening; examplesinclude, but are not limited to, any history of glomerulosclerosis, diabeticnephropathy, lupus nephritis, glomerular nephritis, immunoglobulin A (IgA)nephropathy, and Goodpasture syndrome. NOTE: Participants with chronic renaldisease who meet the criteria for immune compromised (immunosuppressivetherapy) should be enrolled in Stratum B.

6. Is ≥ 65 years of age at the time of randomization but does not meet any ofcriteria 11a through 11e, and is otherwise healthy as determined by theInvestigator.

7. In addition to inclusion criteria 1 through 10 above, participants are eligible tobe included in Primary Stratum B of the study (immunocompromised) only if one ormore of the following criteria apply:

8. Has a solid tumor diagnosis AND has received chemotherapy and/or immunotherapywithin 1 year of screening.

9. Has a diagnosis of a hematologic malignancy within 5 years of screening AND hasreceived any chemotherapy or biologic therapy within 1 year of screening.NOTE: Participants with multiple myeloma may be enrolled regardless of durationof time from diagnosis to screening.

10. Participants who have had a solid organ transplant (SOT) must satisfy all ofthe following:

• Has received a kidney, liver, heart, or lung transplant more than 6 monthsprior to screening
• Is currently receiving at least two immunosuppressive medications

4. Participants who have had a hematopoietic stem cell transplant (HSCT) mustsatisfy at least one of the following:

• Has a history of HSCT (i.e., autologous, allogeneic, bone marrow,peripheral blood stem cell, tandem [peripheral blood and marrow]) within 1year of screening
• Has a history of non-autologous HSCT with graft-versus-host disease (GvHD)requiring active treatment with immunosuppressants (e.g., systemiccorticosteroids ≥1 mg/kg at screening), regardless of the duration of timesince HSCT

5. Is receiving immunosuppressive medicines (e.g., corticosteroids [i.e., at least 20 mg prednisone or equivalent per day], alkylating agents, antimetabolites,transplant-related immunosuppressive drugs, cancer chemotherapeutic agentsclassified as severely immunosuppressive [e.g., Bruton's tyrosine kinaseinhibitors], tumor- necrosis blockers, or other immunosuppressive biologicagents [e.g., for rheumatic diseases]). NOTE: The regimen must be stable (sameagents and doses, or clinically equivalent doses) for ≥2 months prior toScreening to ensure clinical stability (see Inclusion Criterion 7).

6. Has received chimeric antigen receptor-modified T-cell therapy.

7. Has received B-cell depleting therapies (e.g., rituximab, ocrelizumab,ofatumumab, alemtuzumab) within the 12 months prior to screening.

8. Has a diagnosis of any primary or secondary immunodeficiency except IgAdeficiency.

9. Has advanced or untreated human immunodeficiency virus (HIV) infectionmanifested by a cluster of differentiation 4 (CD4) cell count less than 350/cubic millimeter (mm^3) within 6 months of screening.

Exclusion Criteria:

1. A female who is pregnant or lactating.

2. Known or suspected allergy or history of anaphylaxis or other serious adversereactions to zanamivir (following administration of inhaled or intravenousformulations), monoclonal antibodies (including crystallizable fragment [Fc]domains), or any of the components of CD388 or placebo.

3. Has been diagnosed with influenza (i.e., with medical history [including verbal] ofinfluenza) within 6 months prior to randomization.

4. Has received the current seasonal inactivated influenza vaccine or live attenuatedinfluenza vaccine within the 14 days prior to dosing on Day 1. (NOTE: Participantmay have received recombinant influenza vaccine up to the day of dosing on Day 1.)

5. Has an acute (time-limited) or febrile (temperature ≥38.0 degrees Celsius [ºC] [≥100.4 degrees Fahrenheit {ºF}]) illness within 7 days prior to planned dosing onDay 1.

6. Has had close contact (including household contact) with someone withlaboratory-confirmed influenza or SARS-CoV-2 or with someone who has been treatedwith antiviral therapies for influenza or SARS-CoV-2 within the 7 days prior torandomization.

7. Has a clinically unstable condition including, but not limited to, a psychiatriccondition, including recent (within the past year) or active suicidalideation/behavior, or any other condition for which, in the opinion of theInvestigator, may lead to hospitalization or death within the study period and thatsuggests that study enrollment would not be in the participant's best interestand/or that could prevent, confound, or limit the protocol-specified assessments.

8. Has any history of alcohol or drug abuse that, in the opinion of the Investigator,would adversely impact the conduct of the study.

9. Had major surgery (e.g., major cardiac, pulmonary or abdominal operation) within 4weeks prior to randomization, or will not have fully recovered from surgery, or hasmajor surgery planned during the time the participant is expected to participate inthe study.

10. Has severe CKD (equivalent to an eGFR less than 30 mL/min/1.73 m^2 as calculated byCKD-EPI equation for adults or the CKiD U25 equation for adolescents), or isreceiving hemodialysis.

11. Has screening electrocardiogram (ECG) findings of prolonged QT interval correctedusing Fridericia's formula (QTcF) (greater than 450 milliseconds [msec] in males orgreater than 470 msec in females), prolonged PR interval (greater than 220 msec),second- or third-degree heart block, or other clinically significant dysrhythmias,unless participant has a known cardiac diagnosis responsible for the ECG findingsand is in stable condition. NOTE: Participants with cardiac pacemakers may beenrolled if no exclusion criteria are met.

12. Current or planned participation in another clinical study in which studyintervention is being administered during participation in the current study. NOTE:Concurrent enrollment is allowed during the follow-up phase of the other clinicalstudy or in case the study intervention in the other clinical study is a marketedproduct already approved for another indication - exception being if the other studyrequires study interventions that could affect the safety assessments of the presentstudy (e.g., clinical laboratory tests).

13. Receipt within the past 30 days or 5 half-lives (whichever is longer) or anticipatedreceipt of any drug or other biologic agent (e.g., monoclonal antibodies)administered for the prevention or treatment of influenza.

14. Receipt of any formulation of immunoglobulin within 14 days prior to planned studyintervention administration.

15. Receipt of any experimental drug, vaccine, or biologic agent within the 90 days or 5half-lives (whichever is longer) prior to study intervention administration.

16. Has a clinically significant bleeding disorder (e.g., factor deficiency,coagulopathy, or platelet disorder) or medical history of significant bleeding orbruising following intramuscular or SQ injections or venipuncture. NOTE:Participants receiving apixaban or warfarin may be enrolled if the Investigatordetermines risk of SQ treatment with study intervention on Day 1 is minimal.

17. Has donated ≥450 mL of blood product (1 unit) for any reason within 30 days ofscreening.

18. Has direct involvement in the proposed study or other studies under the direction ofthe Investigator, sub-investigators, or at the study site; or is a family member ofan individual with such direct involvement; or is an employee of the Sponsor; or waspreviously enrolled and dosed in a CD388 clinical trial.

19. In the Investigator's judgment, the participant has any condition or circumstancepresent that significantly increases risk, affects the ability to participate,impairs interpretation of study data, or indicates a likelihood of non-adherence tostudy requirements.