Immunogenicity and Safety of an Inactivated Split-virion 2009 Pandemic Influenza A H1N1 Vaccine in Infants

Inclusion Criteria: 1. Healthy infants aged between 6 and 35 months 2. full-term birth with birth weight above 2,500 grams 3. Subject and parent/legal representative should be present at all scheduled visits and to obey all trial procedures Exclusion Criteria: 1. Volunteers in another clinical trial investigating a vaccine, drug, medical device, or medical procedure in the 4 weeks preceding the first trial vaccination 2. Volunteers allergic to ingredient of vaccine composition (can be checked from vaccination history), especially to egg 3. History of progressive or severe neurologic disorder 4. Serious adverse reactions to vaccines such as anaphylaxis, hives, respiratory difficulty, angioedema, or abdominal pain 5. Known or suspected impairment/alteration of immune function, for example receiving immunosuppressive therapy or receiving blood, blood products and/or plasma derivatives or any parenteral immunoglobulin preparation 6. Asthma that is unstable or required emergent care, hospitalization or intubation during the past two years or that required the use of oral or intravenous corticosteroids 7. Bleeding disorder diagnosed by a doctor (e.g. factor deficiency, coagulopathy, or platelet disorder requiring special precautions) or significant bruising or bleeding difficulties with IM injections or blood draws 8. History of thyroidectomy or thyroid disease that required medication within the past 12 months 9. Serious angioedema episodes within the previous 3 years or requiring medication in the previous two years 10. Guillain-Barre Syndrome 11. Self-reported seropositivity for Human Immunodeficiency Virus (HIV), Hepatitis B, or Hepatitis C 12. Any other vaccines or immunoglobulin preparation within 1 weeks prior to enrollment 13. Axillary temperature ≥ 38.0 degrees Celsius within 3 days of intended study vaccination 14. Any conditions may influence the evaluation