FCGR2A and infection: Comparable antibody responses induced by the first A/Yokohama/91/2007 (H1N1) infection (on day 56) were detected in all macaques prior to vaccination and typified by ~2log10-fold increases in IgG levels to A/H1N1 HA, NP and HA Stem with similar trends observed for FcγR2a and FcγR3a usage (Fig 5B).