In Asian adults primed with two doses of AS03A-adjuvanted H5N1 pandemic influenza vaccine , strong cross-clade anamnestic antibody responses were observed after one dose of AS03A-H5N1 heterologous booster vaccine given at Month 6 , 12 , or 36 after priming , suggesting that AS03A-adjuvanted H5N1 vaccines may provide highly flexible prime-boost schedules .