The human family is constantly challenged by viruses, with epidemic/pandemic pathogens either emerging from wildlife or domestic animal reservoirs, or as a consequence of “immune escape” mutations in strains that are circulating in us. Vaccines that promote long -term antibody mediated immunity to “mop-up” any invader can provide immediate protection though, of course, we have no such products when something new and unexpected hits. Our most intimate parasites, viruses grow only within living cells. As a consequence, part of the process of recovery requires the elimination of these cellular “factories” of pathogen production. The “hit man” of immunity that does this job is a circulating white blood cell, the virus-specific, CD8+ “killer” T cell, or cytotoxic T lymphocyte (CTL). We will discuss how this understanding came about, together with emerging evidence that the “recall” of cross-reactive CTL-mediated immunity can provide a measure of protection in the face of an influenza pandemic.