This is an open study of the use of AdimFlu-V (2012-2013 season) vaccine in young healthy subjects. Subjects aged equal to or over 9 years old and less than 18 years old will receive one dose of vaccine (0.5 mL) by intramuscular injection into the upper arm. Subjects aged equal to or over 3 years old and less than 9 years old will received two doses of vaccine (0.5 mL) by intramuscular injection into the upper arm separated by 4 weeks (28 days). Safety outcomes included immediate reactions at the time of vaccination, solicited local and systemic reactions within 7 days after each vaccination, unsolicited adverse events observed since first vaccination to 28 days after the last dose of vaccination, and serious adverse events during the observation. Sera prepared from blood samples will be collected from each subject immediately prior to, and 4 weeks after each vaccination. Anti-hemagglutinin (HA) antibody titers will be determined using the WHO hemagglutination inhibition reference technique. The central laboratory who is responsible for antibody titrations will not be aware of the background of blood samples (e.g., pre- or post-serum), it is also called observer-blinded. All subjects will be followed, either by clinical visit or by telephone contact, for 8 weeks after the last vaccination for safety reasons.

Inclusion Criteria:

1. Boys or non-pregnant girls and aged ≥ 3 through < 18 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 provide the signed study-specific informed consent prior to initiation of any study procedure.

Exclusion Criteria:

1. Subjects received influenza vaccine within the previous 6 months;
2. History of hypersensitivity to eggs or hen's protein, polymyxin B, or neomycin, or similar pharmacological effects to study vaccine;
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, including the common cold or nasal congestion within 72 hours;
6. Subjects with influenza-like illness as defined by the presence of fever (temperature ≥ 38°C) 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 are pregnant, lactating or likely to become pregnant during the study; women of childbearing potential disagree 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 study vaccination;
9. Immunodeficiency, or under immunosuppressive treatment;
10. Receipt of live virus vaccine within 1 month prior to study vaccination or expect receipt within 1 month of study vaccination; receipt of any inactivated vaccine within 2 weeks prior to study vaccination or expected receipt within 1 month of study vaccination;
11. Receipt of any blood products, including immunoglobulin in the prior 3 months;
12. Underlying condition in the investigators' opinion may interfere with evaluation of the vaccine;
13. Significant chronic illness for which inactivated influenza vaccine is recommended or commonly used.