Study of Shenzhen Quadrivalent Inactivated Influenza Vaccine Versus the Shenzhen Trivalent Inactivated Influenza Vaccine in Chinese Subjects From 6 Months of Age

Inclusion criteria : * Aged ≥ 6 months on the day of the first study visit/inclusion * In good health or with underlying medical condition(s) that are judged to be stable by the investigator. Medically-stable is defined as: * No new diagnosis OR * No new class of prescription drug initiated during the 3 months prior to enrollment * For participants aged 6 months through 17 years: Informed consent form has been signed and dated by the parent(s) or another legally acceptable representative, if applicable. Additionally an assent form has been signed and dated by the subject if aged 8 through 17 years (based on local regulations). For subjects aged 18 years and above: Informed consent form has been signed and dated * Subject / subject and parent/legally acceptable representative are able to attend all scheduled visits and to comply with all trial procedures * For subjects aged 6 months to less than 12 months only: Born at full term of pregnancy (≥ 37 weeks) and with a birth weight ≥ 2.5 kg Exclusion criteria: * Subject is 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 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 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 or planned receipt of any vaccine within the period from 2 weeks before trial vaccination to 2 weeks following trial vaccination (or the last trial vaccination) * For previously influenza vaccinated subjects: Previous vaccination against influenza (in the 2019-2020 season) with either the trial vaccine or another vaccine * For previously influenza unvaccinated subjects: Any influenza vaccination (from birth to the day of inclusion) 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 vaccine used in the trial or to a vaccine containing any of the same substances * Self-reported thrombocytopenia or known thrombocytopenia as reported by the parent/legally acceptable representative, contraindicating intramuscular (IM) vaccination * Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating IM 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, is at a stage where it might interfere with trial conduct or completion * Personal history of clinically significant developmental delay (at the discretion of the Investigator), neurologic disorder, or seizure disorder * Known seropositivity for human immunodeficiency virus, including known HIV carrier or patient * Moderate or severe acute illness/infection (according to investigator judgment) on the day of vaccination or febrile illness (axillary temperature ≥ 37.1°C). A prospective subject should not be included in the study until the condition has resolved or the febrile event has subsided * Personal history of Guillain-Barre syndrome * 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 (ie, parent, spouse, natural or adopted child) of the Investigator or employee with direct involvement in the proposed study