Safety and Immunogenicity of High-Dose Quadrivalent Influenza Vaccine in Participants ≥65 Years in the US

This randomized, modified double-blind, active-controlled, multi-center trial assessed the safety and immunogenicity of the high-dose quadrivalent influenza vaccine (QIV-HD) compared to either the licensed or investigational high-dose trivalent influenza vaccine (TIV-HD) in adults.

This randomized, modified double-blind, active-controlled, multi-center trial was conducted in healthy adults (greater than and equal to \[\>=\] 65 years) to assess the safety and immunogenicity (geometric mean titers and seroconversion for the 4 virus strains at 28 days post vaccination) of the QIV-HD compared to one of the TIV-HDs containing either the B strain from the primary lineage (TIV-HD1; licensed vaccine \[Fluzone® High-Dose\] for the 2017-2018 Northern Hemisphere \[NH\] influenza season) or the B strain from the alternate lineage (TIV-HD2, investigational TIV-HD containing an alternate B strain).

Eligibility Criteria:
Inclusion Criteria:

* Aged \>= 65 years on the day of inclusion.
* Informed consent form had been signed and dated.
* Able to attend all scheduled visits and to comply with all trial procedures.

Exclusion Criteria:

* Participation at the time of trial enrollment (or in the 4 weeks preceding the trial vaccination) or planned participation during the present trial period in another clinical trial investigating a vaccine, drug, medical device, or medical procedure.
* Receipt of any vaccine in the 4 weeks (28 days) preceding the trial vaccination or planned receipt of any vaccine prior to Visit 2.
* Previous vaccination against influenza (in the preceding 6 months) with either the trial vaccine or another vaccine.
* Receipt of immune globulins, blood or blood-derived products in the past 3 months.
* Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy, within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months).
* Known systemic hypersensitivity to any of the vaccine components, or history of a life-threatening reaction to the vaccines used in the trial or to a vaccine containing any of the same substances.
* Thrombocytopenia or bleeding disorder, contraindicating IM vaccination based on investigator's judgment.
* Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily.
* Alcohol or substance abuse that, in the opinion of the investigator, might interfere with the trial conduct or completion.
* Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with trial conduct or completion.
* Identified as an Investigator or employee of the Investigator or trial center with direct involvement in the proposed trial, or identified as an immediate family member (i.e., parent, spouse, natural or adopted child) of the Investigator or employee with direct involvement in the proposed trial.
* Personal or family history of Guillain-Barré syndrome.
* Neoplastic disease or any hematologic malignancy (except localized skin or prostate cancer that is stable at the time of vaccination in the absence of therapy and participants who have a history of neoplastic disease and have been disease free for \>= 5 years).
* Moderate or severe acute illness/infection (according to Investigator judgment) on the day of vaccination or febrile illness (temperature \>= 38.0°C \[\>= 100.4°F\]). A prospective participant should not be included in the trial until the condition has resolved or the febrile event had subsided.