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).

- Written informed consent obtained from the participant prior to performance of any
study-specific procedure.

- Phase 1: A male or female 18-64 years of age (YA: 18-64) at the time of the study
intervention administration.

- Phase 2: A male or female 18 years of age and older (YA: 18-64; or OA: more than
equal to [>=]65) at the time of the study intervention administration.

- Participants must have a body mass index (BMI) >=18 kg/m² and less than equal to
(<=) 40 kg/m2.

- Healthy participants or medically stable patients as established by medical history,
clinical examination and (safety laboratory assessments - Phase 1 only).
Participants with chronic medical conditions with or without specific treatment
(e.g., chronic metabolic, cardiac, pulmonary, renal, hepatic, neurologic, and
hematologic diseases) are allowed to participate in this study, if considered by the
investigator as medically stable. A stable medical condition is defined as disease
not requiring significant change in therapy or hospitalization for worsening disease
during 3 months before enrolment.

- Prior receipt of a COVID-19 vaccine. This may be from a completed primary
vaccination series or booster dose(s) of an approved or authorized COVID-19 vaccine.
The last COVID-19 vaccination must have been received at least 90 days prior to
randomization.

- Women of non-childbearing potential may be enrolled in the study.

- Women of childbearing potential may be enrolled in the study if the participant:

- has practiced adequate contraception for 4 weeks prior to study intervention
administration, and

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

- has agreed to continue adequate contraception for at least 8 weeks after
completion of the study intervention administration.

Exclusion Criteria:

Medical conditions

- Only in Phase 1: Any clinically significant hematological, biochemical laboratory
abnormality.

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

- A documented history of confirmed SARS-CoV-2 infection within 90 days before study
vaccination.

- Has had known close contact with anyone who had confirmed influenza or a confirmed
SARS-CoV-2 infection within 2 weeks before study vaccination.

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

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

- Has a bleeding disorder (e.g., factor deficiency, coagulopathy, or platelet
disorder), or prior history of significant bleeding or bruising following IM
injections.

- Any confirmed or suspected immunosuppressive or immunodeficient condition, based on
medical history and physical examination (no laboratory testing required).

- Any history of an immunosuppressive or immunodeficient condition resulting from
disease (e.g., HIV infection or congenital immunodeficiency).

- Has a history of hypersensitivity or severe allergic reaction including anaphylaxis,
generalized urticaria, angioedema, and other significant reactions to any previous
mRNA or non-mRNA vaccine or any component of the study intervention(s) (including
polyethylene glycol, egg proteins and aminoglycoside antibiotics)

- History of uncontrolled neurological disorders or seizures, including Guillain-Barré
syndrome (within 6 weeks of receiving any vaccine) and Bell's Palsy, with the
exception of febrile seizures during childhood.

- History of or current suspicion of myocarditis or pericarditis (including following
administration of an mRNA vaccine); or idiopathic cardiomyopathy, or presence of any
medical condition that increases the risk of myocarditis or pericarditis, including
cocaine abuse, cardiomyopathy, endomyocardial fibrosis, hypereosinophilic syndrome,
hypersensitivity myocarditis, eosinophilic granulomatosis with polyangiitis and
persistent myocardial infection.

- Any other clinical condition that, in the opinion of the investigator, might pose
additional risk to the participant due to participation in the study.

Prior/Concomitant therapy for both Phase 1 and Phase 2

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

- Administration of any mRNA-based vaccine in the period starting 28 days (Day -28)
before study intervention administration.

- Administration of any influenza vaccine within 180 days before enrolment or planned
administration within 28 days (Day 29) after the study intervention administration.

- Phase 1 only: Administration of a vaccine not foreseen by the study protocol in the
period starting 28 days (Day -28) before the study intervention administration or
planned administration within 28 days (Day 29) after the study intervention
administration.

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

- 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.

- Up to 3 months prior to the study intervention administration and up to the end
of study: For corticosteroids, this will mean prednisone equivalent >=-20
mg/day. Inhaled, intra-articular and topical corticosteroids are allowed. If
systemic corticosteroids have been administered short term (<14 days) for
treatment of an acute illness, participants should not be enrolled into the
study until corticosteroid therapy has been discontinued for at least 28 days
before study vaccine administration.

- Up to 3 months prior to study intervention administration and up to the end of
the study: long-acting immune-modifying drugs including among others
immunotherapy (e.g., TNF-inhibitors), monoclonal antibodies, antitumoral
medication.

- Administration of immunoglobulins and/or any blood products or plasma derivatives
within 3 months before study vaccination through end of study.

Prior/Concurrent clinical study experience

• Concurrently participating in another clinical study, at any time during the study
period, in which the participant has been or will be exposed to an investigational or a
non-investigational intervention.

Other exclusion criteria

- Participant is pregnant or has a positive pregnancy test result at Visit 1.

- Participant is breastfeeding or will (re)start breastfeeding between Day 1 (study
vaccination) to 90 days after vaccination.

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

- Participation of any study personnel or their immediate dependents, family, or
household members.

- Participants with conditions precluding the assessment of local reactogenicity at
the injection site (e.g, tattoos, scarring).

- Planned move during the study period that will prohibit participating in the study
until study end.