Figure 4.

HA stem antibodies are neutralising and map to the HA stem for A‐eIIV responses. VNA titres for cH9/1N3 virus measuring HA stem‐mediated neutralisation of A‐eIIV and S‐IIV serum from day 7 post‐vaccination (a) (n = 4 pooled serum in triplicate). YSD H3N2‐1968 library binding to eIIV and control pooled H3N2‐1968 convalescent mouse serum (b) for FACS sorting. Mapping of the yeast clone HA amino acid sequence by serum binding for A‐eIIV (n = 85 clones) and recovered H3N2‐1968 (n = 48 clones) serums (c). YSD binding (b, c), pooled serum from n = 5 mice per group. In (d), the percentage of the population of interest is shown in black on the FACS plots, and the fold change of the percentage versus PBS is shown in red. Experiments were repeated twice, and HA stem amino acid positions are as previously described.29