The second RNA segment of some influenza virus strains encodes a protein called PB1-F2 that might contribute to virulence. Speaking about the 2009 pandemic H1N1 strain, Peter Palese noted that “If this virulence marker is necessary for an influenza virus to become highly pathogenic in humans or in chickens, then the current swine virus doesn’t have what it takes to become a major killer.” If the pandemic virus mutated so that the PB1-F2 protein is produced, would it become a killer?