Flu's success owes much to its genetic mutability

Model flu virus showing surface antigens BOTH "mini-epidemics" of seasonal flu, which happen most years, and much larger pandemics, of which 1918's was the worst example, are the result of an arms race between the influenza virus and the immune systems of the animals it infects. Here's how it works. Type A flu viruses--those which cause pandemics, and also most seasonal flu, have two important surface proteins, haemagglutinin (H) and neuraminidase (N). Haemagglutinin helps the virus invade a tar...