H5N1 influenza viruses isolated from animals and humans since 2003 separate into distinct clades based on hemagglutinin amino acid sequences. According to the invention, multiple clades are used in influenza immunization. Thus there is a prime-boost immunization schedule where a subject receives a priming dose of a first clade of H5 influenza A virus and a boosting dose of a second clade of H5 influenza A virus. There is also an immunogenic composition comprising hemagglutinin antigens from more than one clade of H5 influenza A virus.
