Antigenic shift

The two words "antigenic shift" strike fear in the minds of immunologists and epidemiologists. According to the National Institute of Health (NIH):

http://www3.niaid.nih.gov/topics/Flu/Research/basic/AntigenicShiftIllustration.htm
"The genetic change that enables a flu strain to jump from one animal species to another, including humans, is called antigenic shift."

When the mutation occurs, a more more lethal strain can develop. Today's article exposes this is already happening:

http://www.express.co.uk/posts/view/123818/New-swine-flu-mutation-far-more-deadly-

Let's hope the vaccines and anti-virals remain effective against mutated strains.