Study 1 Kinetics of HI antibody titers induced by different vaccines. Mean HI titers (log2) using (A) H5N1 clade 1 (NIBRG14) and (B) H5N9 antigens in the serum of five groups of vaccinated chickens. One group of SPF chickens was vaccinated with 3 log10 of vFP2211. The four other groups had H5N9 and FP MDA and were vaccinated either with 3 or 5 log10 of vFP2211 at D0, with inH5N9 at D21, or with 5 log10 of vFP2211 at D0 followed by inH5N9 at D21 (prime-boost). HI titers were evaluated at D0, D21 (3 weeks after the vaccination with vFP2211), D42 and D84 (3 and 9 weeks, respectively, after the 2nd vaccination with inH5N9 in the prime-boost group).