Improved resolution of influenza vaccination responses with high-throughput live virus microneutralisation

Influenza remains a significant threat to human and animal health. Assessing serological protection against influenza has relied upon haemagglutinin inhibition assays, which are used to gauge existing immune landscapes, seasonal vaccine decisions and in systems vaccinology studies. Here, we adapt our high-throughput live virus microneutralisation assay for SARS-CoV-2, benchmark against haemagglutinin inhibition assays, and report serological vaccine responsiveness in a cohort of older (>65yo) community dwelling adults (n=73), after the adjuvanted 2021-22 Northern Hemisphere quadrivalent vaccine. We performed both assays against all four viruses represented in the vaccine (A/Cambodia/H3N2/2020, A/H1pdm/Victoria/2570/2019, B/Yamagata/Phuket/2013, BVIC/Washington/02/2019), using sera drawn on days 0 [range: d-28 to d0], 7 [d6-10] and 182 [d161-196] with respect to vaccination. We found population-level concordance between the two assays (Spearman's correlation coefficient range 0.48-0.88; all P less than or equal to 1.4 x 10-5). The improved granularity of microneutralisation was better able to estimate fold-changes of responses, and quantify the inhibitory effect of pre-existing antibody. Our high-throughput method offers an alternative approach to assess influenza-specific serological responses with improved resolution.