The overall CD20+CD27+ memory B cell frequencies (switched and unswitched) (measured by flow cytometry as % of B cells) were 1.57% pre-vaccination (IQR 0.94, 2.33), dropped down to 1.36% (IQR 0.78, 2.01) at Day 3 post-vaccination and gradually returned back to baseline values at Day 28 (1.54%) and Day 75 (1.48%) post-influenza vaccination (S1 Table, Fig. 1). This evidence concerns the gene CD27 and influenza.