Influenza, Human Prevention

This is a randomized, blinded, active-controlled phase III clinical trial to evaluate the immunogenicity and safety of the Quadrivalent Influenza Virus Split Vaccine (QIV) in subjects (aged 3 years and above). Primary immunogenicity endpoints are the geometric mean titers, geometric mean fold increases, seropositive rates, and seroconversion rates of anti-influenza virus HI antibodies for all types 30 days after immunization, and primary safety endpoints are the occurrence of safety events after vaccination including the incidence of adverse events/adverse reactions within 30 minutes/7 days/30 days after immunization, as well as the incidence of serious adverse events/adverse relations within 6 months which will be defined as the secondary safety endpoint. Besides, the secondary endpoints are to evaluate the same index above in different administration programs in children aged 3-8 years.