Figure 8. Neutralizing antibody (NAb) responses in H7N9 patients (pt-1, pt-2 and pt-3) against H7N1 and H7N9 pseudoviruses. Patient sera were collected from 3 H7N9 patients: patient 1 (pt-1) at day 11, patient 2 (pt-2) at day 13 or patient 3 (pt-3) at day 16 after onset of fever; normal human sera (NHS) served as negative control. H7N1 pseudovirus (H7-NL219) expressed H7-HA from A/Netherlands/219/03 (H7N7) and N1-NA from A/VietNam/1203/04 (H5N1) while H7N9 pseudovirus expressed H7 HA from H7N9 A/Zhejiang/U01/2013 and N9 NA from A/Shanghai/02/2013. Neutralizing antibody titers in each patient serum sample were measured at 50% inhibition (IC₅₀) of virus infection to target cells.