This Phase 3 study is a randomized, observer-blind immunogenicity and safety study of aQIV (an MF59-adjuvanted quadrivalent influenza vaccine) compared with a licensed quadrivalent influenza vaccine in adults 50 to 64 years of age.

Inclusion Criteria:

In order to participate in this study, all subjects must meet ALL of the following inclusion criteria:

• Individuals 50 to 64 years of age (i.e. 50 to ≤64 years) on the day of informed consent
• Individuals who have voluntarily given written consent after the nature of the study has been explained according to local regulatory requirements, prior to study entry
• Individuals who can comply with study procedures including follow-up
• Males, females of non-childbearing potential or females of childbearing potential who are using an effective birth control method, at least 30 days prior to informed consent, which they intend to use for at least 2 months after the study vaccination

Exclusion Criteria:

In order to participate in this study, all subjects must not meet ANY of the exclusion criteria described below:

• Females of childbearing potential who are pregnant, lactating, or who have not adhered to a specified set of contraceptive methods from at least 30 days prior to study entry and who do not plan to do so until 2 months after the study vaccination

• Progressive, unstable or uncontrolled clinical conditions

• Hypersensitivity, including allergy, to any component of vaccines, medicinal products or medical equipment whose use is foreseen in this study

• History of any medical condition considered an AESI

• Known history of Guillain Barré syndrome or another demyelinating disease such as encephalomyelitis and transverse myelitis

• Clinical conditions representing a contraindication to intramuscular vaccination and blood draws

• Abnormal function of the immune system resulting from:

  1. Clinical conditions
  2. Systemic administration of corticosteroids (PO/IV/IM) at a dose equivalent to ≥20 mg/day of prednisone for more than 14 consecutive days within 90 days prior to informed consent. Topical, inhaled and intranasal corticosteroids are permitted. Intermittent use (one dose in 30 days) of intra-articular corticosteroids is also permitted
  3. Administration of antineoplastic and immunomodulating agents or radiotherapy within 90 days prior to informed consent

• Received immunoglobulins or any blood products within 180 days prior to informed consent

• Received an investigational or non-registered medicinal product within 30 days prior to informed consent, or who are unwilling to refuse participation in another clinical study at any time during the conduct of this study (notes: i. concomitant participation in a study not involving or no longer involving administration of drugs, vaccines, or medical devices, is acceptable (e.g. studies in safety follow-up phase, observational studies); ii. concomitant participation in a COVID-19 vaccine study is acceptable provided that the vaccine dosing interval mentioned in Exclusion Criterion #11 is adhered to)

• Receipt of any influenza vaccine within 6 months prior to enrollment in this study, or plan to receive influenza vaccine during the study period

• Receipt of any (investigational or licensed) COVID-19 vaccine within 14 days (non-replicating vaccines) or 28 days (replicating vaccines) prior to enrollment or plan to receive any COVID-19 vaccine within 7 days from study vaccination

• Receipt of any inactivated non-influenza vaccine within 14 days or live-attenuated vaccine within 28 days prior to enrollment in this study or plan to receive any other non-influenza vaccine within 28 days from study vaccination

• Acute (severe) febrile illness

• Any other clinical condition that, in the opinion of the investigator, might interfere with the results of the study or pose additional risk to the subject due to participation in the study

• Study personnel or immediate family members or household member of study personnel

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.