Study of a Quadrivalent High-Dose Influenza Vaccine and a Moderna COVID-19 Vaccine Administered Either Concomitantly or Singly in Participants 65 Years of Age and Older Previously Vaccinated With a 2-dose Schedule of Moderna COVID-19 Vaccine

The main purpose of this Phase II study was to assess the safety and immunogenicity of a dose of Fluzone High-Dose (HD) Quadrivalent vaccine and a third dose or booster dose of Moderna coronavirus disease 19 (COVID-19) vaccine administered concomitantly or singly in adults 65 years of age and older having received their second dose of the 2-dose schedule of Moderna COVID-19 vaccine at least 5 months before enrollment in the study.

Participants were in the study for 6 months (approximately 180 days).

Eligibility Criteria:
Inclusion Criteria:

* Aged greater than or equal to \>= 65 years of age on the day of inclusion.
* In good health or with underlying medical condition(s) that were judged to be stable by the Investigator. A stable medical condition was defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment.
* Participants who previously received 2 injections of Moderna COVID-19 Vaccine with the second dose received at least 5 months before Visit 1.
* Abled to attend all scheduled visits and to complied with all study procedures.

Exclusion Criteria:

* 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 3 months preceding planned inclusion).
* Known systemic hypersensitivity to any of the study intervention components, or history of a life-threatening reaction to the study interventions used in the study or to a product containing any of the same substances.
* Previous dermal filler injection (either lips or face fillers).
* Thrombocytopenia, contraindicated IM injection.
* Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicated IM vaccination.
* Chronic illness that, in the opinion of the Investigator, was at a stage where it might interfere with study conduct or completion.
* Moderate or severe acute illness/infection (according to Investigator judgment) on the day of study intervention administration or febrile illness (temperature \>= 100.4°Fahrenheit \[F\] \[38.0° Celsius {C}\]). A prospective participant should not be included in the study until the condition had resolved or the febrile event had subsided.
* History of serious adverse reaction to any influenza or COVID-19 vaccines.
* Personal history of Guillain-Barré syndrome (GBS).
* Personal history of clinically significant developmental delay (at the discretion of the Investigator), neurologic disorder, or seizure disorder.
* Known seropositivity for human immunodeficiency virus, hepatitis B, or hepatitis C.
* Any condition that in the opinion of the Investigator posed a health risk to the participant if enrolled or could interfere with the evaluation of the vaccine.
* Receipt of any vaccine in the 4 weeks preceding the study intervention(s) administration or planned receipt of any vaccine in the period between Visit 01 and 4 weeks following the study intervention(s) administration. Note: Vaccination of Group 3 participants with Fluzone High-Dose Quadrivalent vaccine at the end of the study was not considered by the Sponsor as meeting this exclusion criterion.
* Receipt of blood-derived immune globulins, blood, or blood-derived products in the past 3 months.
* Participation at the time of study enrollment (or in the 30 days preceding the first study vaccination) or planned participation during the present study period in another clinical study investigating vaccine, drug, medical device, or medical procedure.
* Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily.
* Identified as an Investigator or employee of the Investigator or study center with direct involvement in the proposed study, 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 study.
* The above information was not intended to contain all considerations relevant to a participant's potential participation in a clinical trial.