Blood samples from flu shots could shape Tomorrow's vaccines

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Aged 6 months to \< 9 years or \>= 65 years of age on the day of first study vaccination (study product administration). * For infants and toddlers, born at full term of pregnancy (\>=37 weeks) or born after a gestation period of 27 through 36 weeks. * For participants 6 to \< 12 months of age, born at full term of pregnancy (\>= 37 weeks) and with a birth weight \>= 5.5 pound (lbs) (2.5 kilogram \[kg\]). * Informed consent form (ICF) has been signed and dated by participants \>= 65 years of age. * Assent form has been signed and dated by participants 7 to \< 9 years of age, and ICF has been signed and dated by parent(s) or another legally acceptable representative for participants 6 months to \< 9 years of age. * Participants or participant and parent/legally acceptable representative (of participants 6 months to \< 9 years of age) were able to attend all scheduled visits and complied with all study procedures. Exclusion Criteria: * Participants are excluded from the study if any of the following criteria apply: * 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. * Thrombocytopenia, contraindicating IM injection, at the discretion of the Investigator. * Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating 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 \[38.0° Celsius\]). A prospective participant should not be included in the study until the condition has resolved or the febrile event has subsided. * Alcohol, prescription drug, or substance abuse that, in the opinion of the Investigator, might interfere with the study conduct or completion. * 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. * Receipt of any vaccine in the 30 days preceding the first study intervention administration, or planned receipt of any vaccine before Visit 2 for participants receiving 1 dose of influenza vaccine or Visit 3 for participants receiving 2 doses of influenza vaccine. * Previous vaccination against influenza (in the 2021-2022 influenza season) with an investigational or marketed vaccine. * 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 a vaccine, drug, medical device, or medical procedure. Note: Participants might be considered eligible for enrollment if no intervention for the other study occurred within the 30 days prior to the first study vaccination and none were planned before the participant would complete safety surveillance for the present study. The above information was not intended to contain all considerations relevant to a participant's potential participation in a clinical trial.