Primary and secondary response to homotypic PR8 haemagglutinin (HA). (a) Anti‐PR8 HA serum IgG response. Bar shows mean. Px, x days since priming; Bx, x days since boosting; BO, adjuvant‐only primed, PR8 HA boosted, analysed day 6; His, B6 serum sample reactivity with irrelevant C‐terminal His‐tagged protein (Bacillus clausii pdxR). (b) FACs gating strategy. (c) GC B‐cell response to PR8 HA. Bar shows mean. NI, not immunized; other labels as for panel (a). (d) VH mutations in single sorted germinal centre (GC) B cells. From n = 3 mice (Px) and n = 6 mice (Bx). Bar shows median value. Labels as for panel (a). (e) Relative serum IgG avidity for PR8 HA. Bar shows mean. Labels as for panel (a).