The purpose of this study was to evaluate the antibody response to each of the four influenza vaccine strains included in the study vaccine, as measured by hemagglutination inhibition (HAI) at 4 weeks after the last dose of the study vaccine in young subjects aged between 3 years old and 17 years old.

Inclusion Criteria:

1. Boys or girls aged 3 years old to 17 years old on the day of first vaccination;
2. Subject and/or parents(s)/legal guardian(s) must be willing to comply with planned study procedures and be available for all study visits;
3. Subject must be in good physical health on the basis of medical history, physical examination;
4. Subject and/or parents(s)/legal guardian(s) must read and signed the study-specific informed consent prior to initiation of any study procedure.

Exclusion Criteria:

Main exclusion criteria:

1. Subjects received influenza vaccine (Trivalent and/or Quadrivalent) within 6 months prior first vaccination.
2. History of hypersensitivity to eggs or egg protein or similar pharmacological effects to study medication;
3. Personal or family history of Guillain-Barré Syndrome;
4. An acute febrile illness within 1 week prior to vaccination;
5. Current upper respiratory illness (URI), including the common cold or nasal congestion within 72 hours prior to vaccination;
6. Subjects with influenza-like illness as defined by the presence of fever (temperature >38ºC) and at least two of the following four symptoms: headache, muscle/joint aches and pains (e.g. myalgia/arthralgia), sore throat and cough;
7. Female subjects who were pregnant, lactating or likely to become pregnant during the study; Women of childbearing potential disagreed to use an acceptable method of contraception (e.g., hormonal contraceptives, IUD, barrier device or abstinence) throughout the study;
8. Treatment with an investigational drug or device, or participation in a clinical study, within 3 months before consent;
9. Immunodeficiency, or under immunosuppressive therapies;
10. Receipt of live virus vaccine within 1 month prior to study vaccination or expected to receive vaccination before the last blood sampling for immunogenicity evaluation;
11. Receipt of any inactivated vaccine within 2 weeks prior to study vaccination or expected to receive vaccination before the last blood sampling for immunogenicity evaluation;
12. Receipt of any blood products, including immunoglobulin from 3 months before first vaccination to the last blood sampling for immunogenicity evaluation;
13. Underlying condition in the investigators' opinion might interfere with evaluation of the vaccine.

3. Treatment discontinuation

1. Withdrawal criteria i. Subject/Subject's guardians decided to withdraw consent. ii. Lost to follow-up. iii. Administration of prohibited medication/treatment/vaccine. iv. Any pathological event, clinical adverse event, or any change in the subject's status giving indication to the pediatrician that further participation in the study might not be the best interests of the subject, according to investigator's discretion.
2. Contraindications to second vaccination

Subject with any of the following criteria might be contraindicated to take the second vaccination:

i. Had any Grade 3 or Grade 4 adverse reaction within 7 days after first dose. ii. Had any SAE related to first dose during the follow-up of first dose. iii. Any situations met the exclusion criteria, except the exclusion criterion (1) and (8).