A single center, observer-masked, randomized clinical trial is to be conducted in 6-35 months infants to evaluate the safety and immunogenicity of Sinovac's influenza A/H1N1 Vaccine (PANFLU.1).

Inclusion Criteria:

1. Healthy male or female aged between 6 and 35 months
2. Full-term birth, birth weight 2,500 grams or more
3. provided birth certification or vaccination card Parent(s) or legal guardian(s) are able to understand and sign the informed consent

Exclusion Criteria:

1. Cases, cured cases and close contact of influenza A (H1N1) virus
2. Subject that has a medical history of any of the following: allergic history, or allergic to any ingredient of vaccine, such as egg, egg protein, etc
3. Serious adverse reactions to vaccines such as anaphylaxis, hives, respiratory difficulty, angioedema, or abdominal pain
4. Symptoms of acute infection within a week
5. Autoimmune disease or immunodeficiency
6. Congenital malformation, developmental disorders or serious chronic diseases (such as Down's syndrome, diabetes, sickle cell anemia or neurological disorders)
7. 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
8. 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
9. History or family history of convulsions, epilepsy, brain disease and psychiatric
10. Asplenia, functional asplenia or any condition resulting in the absence or removal o the spleen
11. Guillain-Barre Syndrome
12. Administration of 2009-2010 seasonal vaccine
13. History of any blood products within 3 months
14. Administration of any other investigational research agents within 30 days
15. Administration of any live attenuated vaccine within 30 days
16. Administration of subunit or inactivated vaccines within 14 days
17. Be receiving anti-TB prophylaxis or therapy currently
18. Axillary temperature > 37.0 centigrade at the time of dosing
19. Any medical, psychiatric, social condition, occupational reason or other responsibility that, in the judgment of the investigator, is a contraindication to protocol participation or impairs a volunteer's ability to give informed consent