Phase I/II Safety and Immunogenicity of Pandemic Live Attenuated Influenza Vaccine (PLAIV) Candidate Strain A/17/CA/2009/38 (H1N1) in Healthy Thais

Inclusion Criteria: * Healthy * Age 9 - \>49 years old * Having Thai ID card or equivalent * Are seronegative to the specific H1N1 influenza virus determined by antibody titer less than 1:10 by HAI test to the corresponding antigen * Anti HIV - Negative * All hematology \& biochemistry within normal range * Able to read and write and sign written informed consent Exclusion Criteria: * Known history of egg allergy * Having had recently influenza infection confirmed as H1N1 (indeed all other types if Influenza and vaccination with seasonal vaccine will not interfere) * History of bronchial asthma * History of chronic lung diseases * History of chronic rhinitis * History of immunodeficiency state * History of immunosuppression * Acute infectious and noninfectious diseases (within 2 weeks) * Exacerbation of chronic diseases or cancer or HIV positives * Anamnestic leukocytosis, hepatitis B and C positives * The volunteers who have been taking immunoglobulin products or have had a blood transfusion during past three months before the beginning of the experiment * Participation in other research study * Pregnancy or plan to become pregnant for 60 days after enrollment or breast feeding * Any concomitant medication with Aspirin