This is a Phase 1, first-in-human, randomized, placebo-controlled, observer blind study. The effect of two doses of an investigational vaccine on safety, reactogenicity, kinetics and magnitude of the post-vaccination antibody response will be evaluated at different timepoints as compared to placebo in healthy adults.

Approximately 96 evaluable subjects will be enrolled in this study; n=72 receiving investigational vaccine and n=24 receiving placebo.

The study has a screening period (Day -28 to Day -1), a treatment period (Day 1 to Day 43) and a follow-up period (Day 44 to Day 202).

Inclusion Criteria:

1. Individuals 18 to 49 years of age OR 65 to 85 years of age, inclusive on the day of informed consent.
2. Individuals with body mass index (BMI) between 18 and 32 kg/m2, inclusive, at screening .
3. Individuals who can comply with study procedures including follow-up .

Exclusion Criteria:

1. Female participants of childbearing potential who are pregnant, lactating, or who have not adhered to a specified set of highly effective contraceptive methods from at least 30 days prior to informed consent and who do not plan to do so for the duration of the study.
2. Male participants who have not adhered to using barrier contraception such as a condom during at least 60 days after each vaccination, to prevent semen transfer to their sexual partners and prevent pregnancy of a female partner.
3. Progressive, unstable, or uncontrolled clinical conditions
4. Known hypersensitivity or allergy to any study vaccine component
5. Known history of Guillain-Barré syndrome or other demyelinating disease
6. Condition representing a contraindication to vaccination or blood draw
7. Abnormal function of immune system due to clinical condition, medications, or radiotherapy.
8. Receipt or planning to receive blood products, non-study vaccine, influenza vaccine, mRNA-platform vaccine within different timeframes; previous or from study vaccination.
9. Baseline abnormal clinically significant ECG, laboratory safety parameters or vital signs.
10. Plan to donate blood products (other than for this study), sperm, ova, tissues, or organs up to 60 days following the last vaccination.

SEQIRUS supports the release of anonymized subject-level and study-level data in compliance with regulatory requirements, including Clinical Documents which are part of the CTD modules submitted to regulatory agencies for public release.

Summary results disclosure is either in document form (e.g., ICH E3 Clinical Study Report synopsis) or structured data form (such as summary results in ClinicalTrials.gov (United States) or eudract.ema.europa.eu (EU Clinical Trial Registry [EU CTR])).

SEQIRUS discloses results from clinical studies within 12 months of last patient last visit (LPLV) unless otherwise mandated by local laws or regulations.

SEQIRUS will consider requests from qualified scientific and medical researchers to disclose protocols, anonymized subject-level data and study-level data when there is medical, scientific and/or public health interest to ensure the safe use of a Seqirus product licensed on or after 1 January 2014 in the United States (US) and/or the European Union (EU). This applies to Seqirus-sponsored interventional studies initiated after 27 September 2007 and ongoing as of 26 December 2007, that have been included as part of a US or EU submission package which received approval in US and EU on or after 1 January 2014 and have been accepted for publication.