A Study to Evaluate the Immune Response and Safety of a Vaccine Against Influenza in Adults 18-64 Years of Age

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.