Further, it is noteworthy that the H7N9 viruses isolated during the first wave of infection in China in 2013 maintained significant binding affinity for the avian (SAα2,3Gal) receptor, but the continuous circulation of H7N9 until 5th waves lead to more amino acid substitutions within the RBD, resulting in a complete switch to SAα2,6Gal specificity [23]. Here, SAA2 is linked to infection.