A Study to Evaluate the Safety, Pharmacokinetics, and Occurrence of Anti-Drug Antibodies Following Annual Doses of CD388

Inclusion Criteria

• •1. Be willing and able to provide written informed consent and comply with scheduled visits, laboratory tests, and other study procedures.
• •2. Be a male or female adult aged 18 to 66 years of age who previously completed participation in Study CD388.SQ.2.05, having received a SQ CD388 dose of either 150 mg, 300 mg or 450 mg. (Note: Participants in this study may have received seasonal influenza vaccine prior to enrollment in this study and may receive influenza vaccine during this study, with certain exceptions as described in the protocol.)
• •3. Be in stable health at the time of screening and enrollment (in the Investigator's clinical judgment). Participants may not have a history of underlying hematologic, oncologic, renal, autoimmune, cardiac, or pulmonary conditions; or be considered at risk of developing complications from influenza infection per the United States Centers for Disease Control and Prevention (CDC) guidelines (chronic obstructive pulmonary disease \[COPD\], asthma, current immune-compromised cancer \[except non-melanomatous skin cancer\], or diabetes). Study participants will be included based on medical history and vital signs obtained during the screening process.
• •4. Have a body mass index (BMI; calculated as weight in kilograms \[kg\] divided by height in meters \[m\] squared)) of ≥18 kg/m\^2.
• •5. Must agree to the following contraception requirements:
• •a. Females of childbearing potential must use a highly effective, preferably user-independent, method of contraception (failure rate of less than 1 percent per year when used consistently and correctly) from ≥2 weeks prior to enrollment and agree to remain on a highly effective method from Day 1 until 40 weeks after each study intervention administration, the end of relevant systemic exposure. Note: A female is considered of childbearing potential (i.e., fertile) following menarche and until becoming postmenopausal, unless permanently sterile. Permanent sterilization methods include hysterectomy, bilateral salpingectomy, and bilateral oophorectomy. A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. A high follicle stimulating hormone (FSH) level in the postmenopausal range may be used to confirm a postmenopausal state in females not using hormonal contraception or hormonal replacement therapy. However, in the absence of 12 months of amenorrhea, a single FSH measurement is insufficient.
• •Note: Contraceptive (birth control) use by participants should be consistent with local regulations regarding the acceptable methods of contraception for those participating in clinical studies.
• •6. Must agree not to donate blood from Day 1 until 40 weeks after each administration of CD388.
• •7. Must be able to read, understand, and complete protocol questionnaires using the Sponsor-designated diary mode (eDiary or paper) and language, and be willing and able to adhere to the prohibitions and restrictions specified in this protocol. If eDiary is designated, the participant must be able to use a smartphone/tablet/computer. If an appropriate language version is not available in either eDiary or paper, the participant must not be enrolled. The diary mode and approved languages will be designated by the Sponsor prior to study start.
• •8. Must be willing to provide verifiable identification, has means to be contacted, and is able to contact the Investigator/study site and communicate reliably during participation in this study.
• •15. In the opinion of the Investigator, is unlikely to adhere to the requirements of this study.