Matthew Sandbulte and colleagues' new findings presented in PLoS Medicine provide a tantalizing suggestion that immunity to the human influenza virus N1 NA (huN1 NA) cross-reacts with the avian N1 NA (avN1 NA), and that this cross-reactivity may be sufficient to protect against infection with avian influenza virus H5N1 [8]. The gene discussed is XK; the disease is infection.