A Study to Evaluate a Modified RNA Vaccine Against Influenza in Adults 18 Years of Age or Older

This is a Phase 3, randomized, observer-blinded study to evaluate the efficacy, safety, tolerability, and immunogenicity of a single dose of a quadrivalent influenza modRNA vaccine compared to licensed inactivated influenza vaccine in healthy adults 18 years of age and older.

This is a Phase 3, randomized, observer-blinded study to evaluate the efficacy, safety, tolerability, and immunogenicity of a quadrivalent influenza modRNA vaccine (qIRV) encoding HA of 4 seasonally recommended strains (2 A strains and 2 B strains) compared to licensed quadrivalent influenza vaccine (QIV) in healthy adults 18 years of age and older.

Participants may be enrolled in either the reactogenicity subset, immunogenicity subset, or both/neither subset(s). Efficacy will be assessed in this study through surveillance for influenza-like illness.

Eligibility Criteria:
Inclusion Criteria:

1. Male or female participants ≥18 years of age at Visit 1 (Day 1).
2. Participants who are willing and able to comply with all scheduled visits, investigational plan, laboratory tests, lifestyle considerations, and other study procedures.
3. Healthy participants who are determined by medical history, physical examination (if required), and clinical judgment of the investigator to be eligible for inclusion in the study.
4. Capable of giving signed informed consent as described in the protocol, which includes compliance with the requirements and restrictions listed in the ICD and in this protocol.

Exclusion Criteria:

1. Medical or psychiatric condition, including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality, that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
2. History of severe adverse reaction associated with any vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s).
3. Immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination.
4. Bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection.
5. Allergy to egg proteins (egg or egg products) or chicken proteins.
6. Individuals who receive treatment with radiotherapy or immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids (if systemic corticosteroids are administered for ≥14 days at a dose of ≥20 mg/day of prednisone or equivalent), eg, for cancer or an autoimmune disease, or planned receipt throughout the study. Inhaled/nebulized, intra-articular, intrabursal, or topical (skin or eyes) corticosteroids are permitted.
7. Receipt of blood/plasma products or immunoglobulin from 60 days before study intervention administration, or planned receipt throughout the study.
8. Vaccination with any investigational or licensed influenza vaccine within 6 months (175 days) before study intervention administration, or ongoing receipt of chronic antiviral therapy with activity against influenza.
9. Any participant who has received or plans to receive a modRNA-platform SARS CoV-2 vaccine within 14 days before or after study vaccination at Visit 1.
10. Participation in other studies involving administration of a study intervention within 28 days prior to, and/or during, participation in this study.
11. Investigator site staff directly involved in the conduct of the study and their family members, site staff otherwise supervised by the investigator, and sponsor and sponsor delegate employees directly involved in the conduct of the study and their family members.