Overview

This clinical trial will study an investigational seasonal influenza vaccine in adults 18 to 64 years of age. The vaccine is based on messenger ribonucleic acid, also called mRNA. The main goals of the study are to learn how well the vaccine helps the body make an immune response against influenza and what medical problems participants may have after vaccination. Researchers will also compare immune responses in adults 18 to 64 years of age from this study, with immune responses in adults 65 years of age and older from another study. Participants will receive 1 injection into the upper arm muscle and will be followed for about 6 months.

Eligibility

Inclusion Criteria:

• Participants who, in the opinion of the investigator, can and will comply with the requirements of the protocol (e.g., completion of the eDiary, return for follow-up visits, attendance to study contacts, and ability to access and utilize a phone or other electronic communications) independently or with the assistance of a caregiver.
• A male or female participant between and including 18 to 64 years of age at the time of study intervention administration
• Participants of childbearing potential may be enrolled, if the participant:
  • has practiced adequate contraception for at least 30 days prior to study intervention administration, and
  • has a negative urine pregnancy test within 24 hours prior to study intervention administration, and
  • has agreed to continue adequate contraception for at least 8 weeks after study intervention administration.

Exclusion Criteria:

• History of test confirmed influenza infection within 180 days prior to study intervention administration.
• Confirmed or suspected immunosuppressive or immunodeficient condition, except for stable human immunodeficiency virus infection meeting protocol-defined stability criteria.
• History of myocarditis or pericarditis considered causally associated with the administration of an mRNA vaccine.
• History of hypersensitivity or allergic reaction to any previous influenza vaccine.
• History of hypersensitivity or allergic reaction to any previous mRNA vaccine.
• History of Guillain-Barré syndrome (GBS) within 6 weeks of receiving any vaccine.
• Acute or unstable chronic conditions as determined by medical history and clinical examination.
• Administration of an influenza vaccine in the period starting 180 days before the study intervention administration or planned administration prior to Visit 2 during the study.
• Planned administration/administration of prohibited vaccines within protocol-defined time windows before or after study intervention administration.
• Use of any investigational or non-registered product (other than the study intervention during the period beginning 30 days before the dose of study intervention (Day -29 to Day 1), or their planned use during the study period.
• Chronic administration of immune-modifying drugs (defined as more than 14 consecutive days in total) and/or planned use of long-acting immune modifying treatments at any time up to the end of the study.
• Pregnant or lactating female participant.