ST6GAL1 and infection: Comparison of infection into transiently transfected HEKΔSia cells with stable knock-ins of ST6Gal1 or ST3Gal4 in HEKΔSia cells validated the use of the cell-based glycan array as specificity and efficiency of infection by strains WU95Hu−H3 and HU02Av−H5 was similar in both cases (Figure S4G).