This was a blind-observer, monocenter, randomized, comparative, Phase IV study designed to evaluate the immunogenicity and safety of the Sanofi Pasteur Shenzhen Trivalent Influenza Vaccine (SP Shz TIV) versus the Trivalent Influenza Vaccine manufactured by Hualan Biological Engineering Inc (Hualan TIV) comparator in healthy Chinese participants aged 18 to 59 years.

This study is designed to demonstrate the non-inferiority of the immune response in terms of geometric mean titers (GMTs) and seroconversion rates for the 3 strains (A/H1N1, A-H3N2, and B) after a single dose of either the SP Shz TIV or Hualan TIV. Vaccine immune responses will be assessed on Day 0 (pre-vaccination) and Day 28 post-vaccination. Solicited reactions will be collected from Day 0 up to Day 7 after vaccination, unsolicited non-serious adverse events (AEs) will be collected from Day 0 up to Day 28 post-vaccination, and serious AEs will be collected from Day 0 up to 6 months post-vaccination.

Inclusion Criteria:

• Aged ≥ 18 to 59 years on the day of inclusion
• Informed consent form has been signed and dated
• Able to attend all scheduled visits and to comply with all trial procedures

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 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
• Previous vaccination against influenza (in the previous 6 months) with either the trial vaccines or another vaccine
• Receipt of immune globulins, blood or blood-derived product 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 vaccines 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
• Self-reported thrombocytopenia contraindicating intramuscular vaccination
• 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, is at a stage where it might interfere with trial conduct or completion
• 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
• Receipt of oral or injectable antibiotic therapy within 72 hours prior to the first blood draw
• 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

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

An observer-blind procedure will be followed in the study such that neither the Investigator, subject, nor the Sponsor will know which vaccine has been administered.