Cross-Clade Immunogenicity and Antigen-Sparing with an AS03 A -Adjuvanted Prepandemic Influenza Vaccine in a Thai Population

Objective: The present study (NCT00449670) in Asian subjects (18-60 years) evaluated the manufacturing consistency of four formulations of 3.75mg AS03A-adjuvanted H5N1 influenza vaccine, in terms of post-immunization Hemagglutination Inhibition (HI) titers against the A/Vietnam/1194/2004 and A/Indonesia/05/2005 strains. The immunogenicity and safety of the vaccine in the Thai population are reported herein. Material and Method: Subjects were randomized (2:2:2:2:1:1) between four vaccine groups and two control groups to receive two doses of either the AS03A-adjuvanted or non-adjuvanted H5N1 vaccine formulations, 21 days apart. Sera were assayed for HI antibody titers against the two strains. Results: After the second dose of AS03A-adjuvanted vaccine, 94.2% subjects in the H5N1-AS03A groups seroconverted and 94.9% subjects were seroprotected against the A/Vietnam/1194/2004 strain. Cross-clade immune response against the A/Indonesia/05/2005 strain was observed. All vaccine formulations had an acceptable safety profile. Conclusion: This antigen-sparing AS03A-adjuvanted influenza vaccine could be a suitable candidate for combating and mitigating future influenza pandemics. Keywords: H5N1, Thailand, Adjuvant System, Influenza, Prepandemic