Study of CD388 for the Prevention of Influenza in Subjects Not at Risk for Influenza Complications

Inclusion Criteria:

1. Willing and able to provide written informed consent and comply with scheduledvisits, laboratory tests, and other study procedures.

2. Males and females 18 to less than 64 years of age.

3. In the Investigator's clinical judgment, is in stable health at the time ofscreening and randomization. Participants may not have underlying hematologic,oncologic, renal, autoimmune, and/or cardiopulmonary illnesses or be considered atrisk of developing complications from influenza infection per the CDC guidelines (chronic obstructive pulmonary disease [COPD], asthma, immune compromised currentcancer [except non-melanomatous skin cancer], or diabetes). Subjects will beincluded on the basis of medical history and vital signs taken between signing ofthe informed consent and randomization.

4. Body mass index (BMI; calculated as weight in kilograms [kg] divided by height inmeters [m] squared) of 18.0 kg/m^2 to 35.0 kg/m^2 (inclusive).

5. Women of childbearing potential (WOCBP) must:

6. Have a negative pregnancy test (beta-human chorionic gonadotropin [β-hCG]) atscreening, AND

7. Be practicing a highly effective, preferably user-independent method ofcontraception (failure rate of less than 1 percent per year when usedconsistently and correctly) from ≥2 weeks prior to randomization and agrees toremain on a highly effective method from Day 1 until 32 weeks after study drugadministration, the end of relevant systemic exposure. The Investigator shouldevaluate the potential for contraceptive method failure (e.g., noncompliance,recently initiated) in relationship to the day of administration of study drug. A woman is considered of childbearing potential (i.e., fertile) following menarcheand until becoming postmenopausal, unless permanently sterile. Permanentsterilization methods include hysterectomy, bilateral salpingectomy, and bilateraloophorectomy. A postmenopausal state is defined as no menses for 12 months withoutan alternative medical cause. A high follicle stimulating hormone (FSH) level in thepostmenopausal range may be used to confirm a postmenopausal state in women notusing hormonal contraception or hormonal replacement therapy. However, in theabsence of 12 months of amenorrhea, a single FSH measurement is insufficient.

8. Female participants must agree not to donate or freeze eggs (ova, oocytes) forfuture use for the purposes of assisted reproduction from Day 1 until 32 weeks afterstudy drug administration.

9. Male participants must wear a condom when engaging in any activity that allows forpassage of ejaculate to another person from Day 1 until 32 weeks after study drugadministration. Male participants should also be advised of the benefit for a femalepartner to additionally use a highly effective method of contraception, as condomscould break or leak. Note: Contraceptive (birth control) use by participants should be consistent withlocal regulations regarding the acceptable methods of contraception for thoseparticipating in clinical studies.

10. Male participants must agree not to donate sperm from Day 1 until 32 weeks afterstudy drug administration.

11. Participant agrees not to donate blood from Day 1 until 32 weeks after study drugadministration.

12. Must be able to read, understand, and complete questionnaires in the electronicdiary (eDiary), work with smartphones/tablets/computers, and be willing and able toadhere to the prohibitions and restrictions specified in this protocol. If anappropriate language version is not available for the eDiary assessments, theparticipant should not be enrolled.

13. 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.

Exclusion Criteria:

1. 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.

2. Have been diagnosed with influenza (i.e., with medical history [including verbal] ofinfluenza) within the past 6 months prior to randomization.

3. Has received the current seasonal influenza vaccine prior to screening or isplanning to receive the seasonal vaccine during trial participation.

4. Has an acute illness (including acute respiratory illnesses) or body temperature ≥38.0ºC (≥100.4 degrees Fahrenheit [ºF]) within 7 days prior to study drugadministration (Note: Enrollment at a later date, subsequent to resolution [withinthe screening period] is permitted).

5. Has had close contact (including household contacts) with someone withlaboratory-confirmed influenza or with someone who has been treated with antiviraltherapies for influenza within the past 7 days prior to randomization.

6. Has had close contact (including household contacts) with someone with severe acuterespiratory syndrome coronavirus 2 (SARS-CoV-2) infection or coronavirus disease 2019 (COVID-19) as defined by the US CDC or has had a positive SARS-CoV-2 testwithin 10 days prior to screening. Please note SARS-CoV-2 testing is NOT requiredduring screening.

7. Has a serious and/or clinically unstable condition such as psychiatric condition,including recent (within the past year) or active suicidal ideation/behavior,Alzheimer's disease, or any other condition for which, in the opinion of theInvestigator, participation would not be in the participant's best interest or thatcould prevent, confound, or limit the protocol-specified assessments.

8. Any history of alcohol or drug abuse within the past 2 years or a positive urinedrug screen for drugs of abuse (other than tetrahydrocannabinol [THC]) at screeningor Day 1. Note: urine drug screen that is positive for a medication prescribed fortreatment of ongoing condition is not exclusionary.

9. Had major surgery (e.g., major cardiopulmonary or abdominal operations) perInvestigator judgment within 4 weeks prior to randomization, or will not have fullyrecovered from surgery, or has major surgery planned during the time the participantis expected to participate in the study.

10. Screening ECG findings of prolonged QT interval corrected for heart rate usingFridericias formula (QTcF) (greater than 450 milliseconds [msec] in males or greaterthan 470 msec in females), prolonged PR interval (greater than 220 msec), second- orthird-degree heart block, or other clinically significant dysrhythmias.

11. At the time of screening, any finding that may significantly increase the risk ofparticipation in the study, affect the ability to participate in the study, orimpair interpretation of the study data.

12. Current or planned participation in another clinical study where study interventionis being administered while participating in the current study. Note: Concurrentenrollment is allowed during the follow-up phase of the other clinical study or incase the study intervention in the other clinical study is a marketed productalready 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. [Exclusion criterion #13 removed during Amendment 1.1-US; placeholder remains toretain numbering of the remaining original exclusion criteria.]

14. Prior receipt within the past 30 days or 5 half-lives (whichever is longer) oranticipated receipt of any drug, vaccine, or other biologic agent (e.g., monoclonalantibodies) administered for the prevention or treatment of influenza.

15. Prior receipt of any experimental drug, vaccine, or biologic agent within the past 90 days or 5 half-lives (whichever is longer).

16. Contraindication to SQ injections and blood draws (e.g., bleeding disorders).

17. Has donated ≥450 mL of blood product (1 unit) for any reason within 30 days ofscreening or plans to donate blood product during the study.

18. Currently pregnant or breastfeeding, intends to become pregnant or breastfeed, orhas a positive pregnancy test during the screening period.

19. Has direct involvement in the proposed study or other studies under the direction ofthe Investigator, sub-investigators, or study site; is a family member of anindividual with such direct involvement; or is an employee of the Sponsor.

20. In the opinion of the Investigator, is unlikely to adhere to the requirements of thestudy.