This was a randomized, laboratory-blinded study in healthy male and non-pregnant female designed to investigate the safety, reactogenicity, and immunogenicity of an inactivated influenza H1N1 vaccine (AdimFlu-S). In the adult cohort, all volunteers were randomized in a 1:1:1 ratio to receive 2 injections of AdimFlu-S (A/H1N1) 15 mcg HA at 3 weeks apart, 2 injections of AdimFlu-S (A/H1N1) 30 mcg HA at 3 weeks apart or 1 injection of AdimFlu-S (A/H1N1) 15 mcg HA. In the elders cohort, all volunteers were randomized in a 1:1 ratio to receive 2 injections of AdimFlu-S (A/H1N1) 15 mcg HA at 3 weeks apart or 2 injections of AdimFlu-S (A/H1N1) 30 mcg HA at 3 weeks apart.

Following immunization, safety was measured by assessment of adverse events for 6 weeks following the first vaccination, serious adverse events and new-onset chronic medical conditions through 7 months post first vaccination; and reactogenicity to the vaccines for 7 days following each vaccination. Immunogenicity testing included hemagglutinin inhibition (HAI) testing on serum obtained before first vaccination, and three and six weeks after first vaccination.

Inclusion Criteria:

• Males or non-pregnant females and age ≧ 18 years;
• Willing and able to adhere to visiting schedules and all study requirements;
• In good physical health on the basis of medical history, physical examination;
• Subject should read and sign the study-specific informed consent.

Exclusion Criteria:

• Subject ever received influenza vaccine within the previous 6 months;
• History of hypersensitivity to eggs or egg protein or similar pharmacological effects to study medication (AdimFlu-S (A/H1N1));
• Personal or family history of Guillain-Barré Syndrome;
• An acute febrile illness within the last 72 hours prior to vaccination;
• Subjects, with bleeding or any coagulation disorder, who receive anticoagulants in the preceding 3 weeks, thus posing a contraindication for intramuscular injection;
• Subjects with influenza-like illness as defined by the presence of fever (temperature ≧38.5℃) and at least two of the following four symptoms: headache, muscle/joint aches and pains (e.g. myalgia/arthralgia), sore throat and cough;
• Female subjects who are pregnant, lactating or likely to become pregnant during the study. Women of childbearing potential who disagree to use an acceptable method of contraception (e.g., hormonal contraceptives, IUD, barrier device or abstinence) throughout the study;
• Treatment with an investigational drug or device, or participation in a clinical study, within 3 months before consent;
• Immunodeficiency, immunosuppressive or household contact with immunosuppression;
• History of wheezing or have been using bronchodilator within 3 months prior to study vaccination;
• Receipt of live virus vaccine within 1 month prior to study vaccination or expected receipt within 2 months after first study vaccination;
• Receipt of any inactivated vaccine within 2 weeks prior to study vaccination or expected receipt of vaccination within 3 weeks after the immunogenicity evaluation period;
• Receipt of any blood products, including immunoglobulin in the prior 3 months;
• Underlying condition, in the investigator's opinion, that may be inappropriate for vaccination;
• Significant chronic illness for which inactivated influenza vaccine is recommended or commonly used.