For example, US influenza seasons where circulating viruses saw more mutations in antigenic sites of the hemagglutinin (HA) and neuraminidase (NA) surface proteins were associated with larger epidemic size41, and the viral composition of the 2017/2018 US A/H3N2 season was consistent with dominance of the viruses to which population immunity as measured using standard serological assays was lowest46. The gene discussed is XK; the disease is influenza.