Nash, here's the basics:
The bird flu virus (H5N1) is spreading throughout the wild and domestic bird populations. The virus can infect humans and cause a severe and often fatal form of flu. But so far, the virus doesn't spread from person to person -- the only way to get it is from sick birds. And the vast majority of people don't spend a lot of time around sick birds so it's no big deal.
The worry is that the virus could mutate, allowing person-to-person transmission. Recent studies have shown this has happened before, most notably in the 1918 pandemic that killed millions of people. If this happens, it will be difficult to contain and would become a very big deal.
The chance of this mutation is stochastic -- essentially random -- a roll of the dice. So nobody can predict when and if this will happen. But as the virus becomes more and more common in birds, the chances of such a mutation goes up -- the more times you roll the dice, the more chance of eventually getting snake eyes.
Originally posted by Ripsnort
The older, healthier folks who've been exposed to many flu viruses have a better chance of fighting it off.
Not necessarily. Nobody has immunity to H5N1, because they've never been infected before. There would be very little cross immunity to a different flu strain -- that's why they have to create a new flu vaccine every year, the strains mutate. The mortality rate of the 1918 pandemic was especially high in young adults.
