The A/Fujian/411/02(H3N2)-like clinical Danish viruses had several substitutions in HA at sites that might influence the virus' capability for egg growth [10, 37] . These include; A131T, I144N, H155T, Q156H, W222R and G225D. The A/California/20/99(H3N2)-like viruses had further changes at positions K145S/N, Y159F, S193F and V226I and A/Wisconsin/67/05(H3N2) possessed in addition S193F and D225N. All isolates after the 1999-2000 A/Moscow/10/99(H3N2)-like viruses possess S186G. In recent years H3N2 viruses have had poor replication efficiency in eggs [54, 55] . It has been shown that positions 186, 226 and 196 are critical determinants for egg growth.