A Study to Assess the Safety and Immune Response of a Vaccine Against Influenza in Healthy Younger and Older Adults

Inclusion Criteria:

• A male or female between and including 18 and 50 years of age in Phase 1 and betweenand including 18 and 85 years of age (YA: 18-64; OA: 65-85) in Phase 2 at the timeof the study intervention administration.

• Healthy participants or medically stable participants as established by medicalhistory, clinical examination, and safety laboratory assessments. Participants withchronic medical conditions with or without specific treatment are allowed toparticipate in this study if considered by the investigator as medically stable. Astable medical condition is defined as disease not requiring significant change intherapy or hospitalization for worsening disease during 3 months before enrollment.

• Body mass index (BMI) >=18 kilograms per meter square (kg/m^2) and less than orequal to (<=) 35 kg/m^2.

• Participants who, in the opinion of the investigator, can and will comply with therequirements of the protocol.

• Written informed consent obtained from the participant prior to performing anystudy-specific procedure.

• Female participants of non-childbearing potential may be enrolled in the study.

• Female participants of childbearing potential may be enrolled in the study if theparticipant:

• has practiced adequate contraception for 28 days prior to study interventionadministration, and

• has a negative pregnancy test on the day of study intervention administration, and

• has agreed to continue adequate contraception for at least 1 month after studyintervention administration

Exclusion Criteria:

Medical conditions

• Only in Phase 1: Any clinically significant* hematological, biochemical, urinalysisor (hemoglobin A1c) HbA1c laboratory abnormality.

*The investigator should use the clinical judgment to decide which abnormalities areclinically significant.

• Participant tested positive for influenza by local health authority-approved testingmethods within 180 days prior to Day 1.

• Current or past malignancy, unless completely resolved without clinicallysignificant sequelae for >5 years.

• Any confirmed or suspected immunosuppressive or immunodeficient condition, includingHIV infection, based on medical history and physical examination (no laboratorytesting required). However, in Phase 2, HIV-infected individuals may be enrolled ifparticipants have been stable on antiretroviral therapy for the past 6 consecutivemonths, i.e., their treatment has not been modified, their cluster ofdifferentiation 4 (CD4) cell count is >=200/cubic millimeter (mm^3) and their viralload has been undetectable (i.e., HIV-RNA less than (<) 50 copies/milliliter [mL]) (based on medical records, no laboratory testing required).

• History of myocarditis or pericarditis less than or equal to 10 years prior tovaccine administration, including a history of myocarditis or pericarditis followingvaccination with an mRNA coronavirus disease 2019 (COVID-19) vaccine.

• Participants with history of hypersensitivity or severe allergic reaction to anyprevious vaccine or hypersensitivity likely to be exacerbated by any component ofthe study intervention (including latex, polyethylene glycol, egg protein andaminoglycoside antibiotics).

• History of, or uncontrolled neurological disorders or seizures, includingGuillain-Barré syndrome and Bell's palsy, with the exception of febrile seizuresduring childhood.

• Any history of dementia or any medical condition that moderately or severely impairscognition.

• Any medical condition that in the judgment of the investigator would makeintramuscular injection unsafe.

• Any other clinical condition that, in the opinion of the investigator, might poseadditional risk to the participant due to participation in the study.

Prior/Concomitant therapy

• Administration of an influenza vaccine (including any of the study investigationalvaccines) within 180 days before enrollment or planned administration within 28 days (Day 29) after the study intervention administration.

• Phase 1: Administration of a vaccine not foreseen by the study protocol in theperiod starting 28 days (Day -28) before the study intervention administration orplanned administration within 28 days (Day 29) after the study interventionadministration. Phase 2: Administration of a vaccine not foreseen by the studyprotocol in the period starting 15 days (Day -15) before the study interventionadministration or planned administration within 28 days (Day 29) after the studyintervention administration.

*In case emergency mass vaccination for an unforeseen public health threat isrecommended and/or organized by public health authorities outside the routineimmunization program, the time period described above can be reduced to 7 days if,necessary for that vaccine, provided it is used according to the local governmentalrecommendations and that the Sponsor is notified accordingly.

• Use of any investigational or non-registered product (drug, vaccine, or invasivemedical device) other than the study intervention during the period beginning 30days before the study intervention administration, or their planned use during thestudy period.

• Administration of long-acting immune-modifying drugs within 90 days beforeenrollment or planned use at any time during the study period.

• Administration of immunoglobulins and/or any blood products or plasma derivativesduring the period starting 90 days before the study intervention administration, orplanned administration during the study period. Administration of monoclonalantibodies specifically directed against the spike protein of Severe AcuteRespiratory Syndrome Coronavirus 2 (SARS-CoV-2), for treatment of COVID-19 diseaseis allowed.

• Chronic administration (defined as more than 14 days in total) of immunosuppressantsor other immune-modifying drugs during the period starting 3 months prior to thestudy intervention administration. For corticosteroids, this will mean prednisoneequivalent >=20 milligrams (mg)/day. Inhaled, topical and intraarticular steroidsare allowed.

Other exclusions

• Concurrently participating in another clinical study, at any time during the studyperiod, in which the participant has been or will be exposed to an investigationalor a non-investigational intervention (drug/invasive medical device).

• Pregnant or lactating female.

• Bedridden participants.

• Female planning to become pregnant or planning to discontinue contraceptiveprecautions within the 1-month post-dosing period.

• Alcoholism or substance use disorder within the past 24 months based on the presenceof 2 or more of the following abuse criteria: hazardous use, social/interpersonalproblems related to use, neglect of major roles to use, withdrawal, tolerance, useof larger amounts or longer, repeated attempts to quit or control use, much timespent using, physical or psychological problems related to use, activities given upto use, craving.

• Any study personnel or their immediate dependents, family, or household members.

• Participants with extensive tattoos covering deltoid region on both arms that wouldpreclude the assessment of local reactogenicity.