The primary objectives of this study were:

• To describe the immunogenicity of the 2018-2019 formulation of Fluzone® Quadrivalent vaccine in children 6 to less than (<) 36 months of age and 3 to <9 years of age, and in adults 18 to <65 years of age; the immunogenicity of the 2018-2019 formulation of Flublok® Quadrivalent vaccine in adults 18 to <65 years of age; and the immunogenicity of the 2018-2019 formulation of Fluzone High-Dose vaccine in adults greater than or equal to (>=) 65 years of age.
• To describe the safety of the 2018-2019 formulation of Fluzone Quadrivalent vaccine in children 6 to <36 months of age and 3 to <9 years of age, and in adults 18 to <65 years of age; the safety of the 2018-2019 formulation of Flublok Quadrivalent vaccine in adults 18 to <65 years of age; and the safety of the 2018-2019 formulation of Fluzone High-Dose vaccine in adults >=65 years of age.

Study duration per participant was approximately 21 days for adult participants or 28 days for child participants who received one dose of vaccine, and 56 days for participants who received two doses of vaccine.

Inclusion criteria :

• Aged 6 months to <9 years or >=18 years on the day of first study vaccination (study product administration).
• For participants 6 to <12 months of age, born at full term of pregnancy (>=37 weeks) and with a birth weight >=2.5 kilograms (kg) (5.5 pounds [lbs.]).
• Informed consent form (ICF) had been signed and dated by participants >=18 years of age.
• Assent form had been signed and dated by participants 7 to <9 years of age, and ICF had been signed and dated by parent(s) or guardian(s) for participants 6 months to <9 years of age.
• Participants and parent/guardian (of participants 6 months to <9 years of age) were able to attend all scheduled visits and to comply with all study procedures.

Exclusion criteria:

• Participant was pregnant, or lactating, or of childbearing potential and not using an effective method of contraception or abstinence from at least 4 weeks prior to vaccination and until at least 4 weeks after vaccination. To be considered of non-childbearing potential, a female must be pre-menarche, or post-menopausal for at least 1 year, or surgically sterile.
• 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 a vaccine, drug, medical device, or medical procedure.
• Receipt of any vaccine in the 30 days preceding the first study vaccination, or planned receipt of any vaccine before Visit 2 for participants who received 1 dose of influenza vaccine or Visit 3 for participants who received 2 doses of influenza vaccine.
• Previous vaccination against influenza (in the 2018-2019 influenza season) with either study vaccine or another vaccine.
• Receipt of immune globulins, blood, or blood-derived products in the 3 months preceding planned inclusion.
• Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy, within the 6 months preceding planned inclusion; 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 vaccine components, or history of a life- threatening reaction to study vaccine or to a vaccine containing any of the same substances.
• Thrombocytopenia, which might be a contraindication for intramuscular vaccination, at the discretion of the Investigator.
• Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating intramuscular vaccination.
• Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily.
• Current alcohol abuse or drug addiction.
• 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 planned vaccination or febrile illness (temperature >=100.4 degree Fahrenheit [38.0 degree Celsius]). A prospective participant was not included in the study until the condition had resolved or the febrile event had subsided.
• Identified as an Investigator or employee of the Investigator or study center with direct involvement in the proposed study (participants >=18 years of age) 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 (all participants).
• History of serious adverse reaction to any influenza vaccine.
• Personal history of Guillain-Barré syndrome.
• Any condition that in the opinion of the Investigator would pose a health risk to the participant if enrolled or could interfere with the evaluation of the vaccine.
• 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.

The above information was not intended to contain all considerations relevant to a participant's potential participation in a clinical trial.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org