Hemagglutination titers of recent viruses with chicken and human red blood cells. The viruses were grown in MDCK cells and concentrated by centrifugation to obtain a ratio of HA titer with chicken red cells compared to human red cells. For Mem/31/98, OK/323/03 and OK/369/05 there was still no agglutination of chicken red blood cells. The 2006 viruses were not concentrated. The data are average ± standard deviation of 3 experiments.