A Study to Find and Confirm the Dose and Assess Safety, Reactogenicity and Immune Response of a Vaccine Against Pandemic H5N1 Influenza Virus in Healthy Younger and Older Adults

Inclusion Criteria:

• A male or female between and including 18 and 64 yoa (i.e., 64 years + 364 days;YAs) or between and including 65 and 85 yoa (i.e., 85 years + 364 days; OAs) at thetime of the first study intervention administration.

• Participants, who, in the opinion of the investigator, can and will comply with therequirements of the protocol (e.g., completion of the eDiary, return for follow-upvisits).

• Body mass index (BMI) more than or equal to (≥)18 kilogram per square meter (kg/m²)and less than or equal to (≤) 35kg/m².

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

• Healthy participants or medically stable patients as established by medical history,clinical examination, and screening safety laboratory assessments (Where applicable)Participants with chronic medical conditions with or without specific treatment (e.g., chronic metabolic, cardiac, pulmonary, renal, hepatic, neurologic, andhematologic diseases) are allowed to participate in this study, if considered by theinvestigator as medically stable. A stable medical condition is defined as diseasenot requiring change in therapy or hospitalization for worsening disease during 3months before enrollment.

• Females of nonchildbearing potential may be enrolled in the study.

• Females of childbearing potential may be enrolled in the study, if the participant:

• has practiced adequate contraception for 1 month prior to study interventionadministration, and

• has a negative pregnancy test at Screening Visit (if applicable) and on the dayof each study intervention administration, and

• has agreed to continue adequate contraception for at least 1 month aftercompletion of the last dose of study intervention.

Exclusion Criteria:

Medical conditions

• Where applicable, FDA toxicity grades will be exclusionary.

• Planned administration of an influenza vaccine before Day 43 time point.

• Current or past malignancy, unless completely resolved without clinicallysignificant sequelae (e.g., no evidence of disease following successful treatment ofbasal cell carcinoma cases are allowed) for >5 years.

• Has any medical disease or psychiatric condition that, in the opinion of theinvestigator, precludes study participation because it would place the participantat an unacceptable risk of injury, would render them unable to meet the requirementsof the protocol, or may interfere with successful completion of the study.

• Has a bleeding disorder (e.g., factor deficiency, coagulopathy, or plateletdisorder), or prior history of significant bleeding or bruising followingintramuscular (IM) injections.

• 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 ifthey have been stable on antiretroviral therapy for the past 6 consecutive months,i.e., their treatment has not been modified, their CD4 cell count is ≥200/mm³ andtheir viral load has been undetectable (i.e., HIV-RNA <50 copies/mL) (based onmedical records, no laboratory testing required).

• History of any reaction or hypersensitivity likely to be exacerbated by anycomponent of the study intervention(s) (including polyethylene glycol,aminoglycoside antibiotics and egg products).

• History of uncontrolled neurological disorders or seizures, including Guillain-Barrésyndrome and Bell's palsy, with the exception of febrile seizures during childhood.

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

• History of or current suspicion of myocarditis or pericarditis (including followingadministration, of an mRNA vaccine); or idiopathic cardiomyopathy, or presence ofany medical condition that increases the risk myocarditis or pericarditis, includingcocaine abuse, cardiomyopathy, endomyocardial fibrosis, hypereosinophilic syndrome,hypersensitivity myocarditis, eosinophilic granulomatosis with polyangiitis andpersistent myocardial infection.

• 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

• Use of any investigational or non-registered product (drug, vaccine, or invasivemedical device) other than the study intervention(s) during the period beginning 28days before the dose of study intervention(s) (Day -28 to Day 1), or their planneduse during the study period.

• Administration of a vaccine not foreseen by the study protocol in the periodstarting 28 days before the study intervention administration or plannedadministration within 21 days after the (last) study intervention administration*.

*If emergency mass vaccination for an unforeseen public health threat (e.g., apandemic) is recommended and/or organized by public health authorities outside theroutine immunization program, the time period described above can be reduced to 7days if, necessary for that vaccine, provided it is used according to the localgovernmental recommendations and that the Sponsor is notified accordingly.

• Chronic administration of immune-modifying drugs (defined as more than 14consecutive days in total) and/or planned use of long-acting immune-modifyingtreatments at any time up to the end of the study.

• Up to 3 months prior to the study intervention administration:

• For corticosteroids, this will mean prednisone equivalent 20 mg/day. Inhaled,intra-articular and topical corticosteroids are allowed. If systemiccorticosteroids have been administered short term (<14 days) for treatment ofan acute illness, participants should not be enrolled into the study untilcorticosteroid therapy has been discontinued for at least 28 days before studyvaccine administration.

• Up to 3 months prior to study intervention administration: long-actingimmune-modifying drugs including among others immunotherapy (e.g.,TNF-inhibitors), monoclonal antibodies, antitumoral medication.

• Administration of immunoglobulins and/or any blood products or plasma derivativeswithin 3 months before study intervention administration through end of study.

Prior/concurrent clinical study experience

• 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).

• Participated in an A(H5) influenza vaccine study in the past or have a history ofA(H5) influenza infection prior to dosing in this study. This includes influenzasubtypes A(H5N1), A(H5N8), A(H5N6).

Other exclusion criteria

• Pregnant or lactating female participant.

• Female planning to become pregnant or planning to discontinue contraceptiveprecautions within 1 months after completion of the vaccination series.

• Has a history of chronic alcohol consumption and/or drug abuse as deemed by theinvestigator to render the potential participant unable/unlikely to provide accuratesafety reports or comply with study procedures.

• 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.

• Planned move during the study period that will prohibit participating in the studyuntil study end.

• Donation of blood 3 months prior to the study intervention administration and duringthe study period.