a, Representative plots of surface influenza virus HA and S staining in CD20+CD38lo/intIgDloCD19+CD3− live singlet memory B cells (gating in Extended Data Fig. 1d) from PBMCs from control individuals (left) and convalescent individuals 7 months after symptom onset (right). b, Kinetics of S- (top) and HA- (bottom) binding memory B cells in PBMCs from convalescent individuals, collected at the indicated days after symptom onset. Data from the 7-month time point are also shown in c. c, Frequencies of S- (left) and HA- (right) binding memory B cells in PBMCs from control individuals (black circles) and convalescent individuals 7 months after symptom onset (white circles). The dotted line in the left plot indicates the limit of sensitivity, which was defined as the median + 2× s.d. of the controls. Each symbol represents one sample (n = 18 convalescent, n = 11 control). Horizontal lines indicate the median. P values from two-sided Mann–Whitney U tests.