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Originally Posted by Ken G
That does seem like a valid point. But where did the avian flu come from? It's new to birds obviously-- by what you're saying, it must have come from something else that was used to it and had immunity to it (or else we have to keep looking for other sources, ad infinitum). I wonder what that was, and if there is already immunity there, perhaps it would help us find a vaccine?
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Flu viruses circulate in birds just as they do in humans and many other species. Every so often chance mutation allows the virus to invade more readily, make mores copies, make a deadly enzyme or any number of other changes that cause a higher fatality rate. In the case of flu viruses, not only do they mutate, but they also reassort their genes with other flu strains leading to new combinations just like human offspring are a mix of the parents. This makes new strains particularly common with this virus family.
We have a vaccine. The problem is making enough of it fast enough. And the second problem is adjusting the vaccine in time when the virus shifts genetically to become contagious among humans. We can't predict those changes ahead of time and we can't make vaccine in less than a few months.
In 1918 the flu virus spread worldwide in 4 months without air travel. It not only takes that long to make vaccine, the vaccine manufacturers met 2 years ago in Europe and predicted if all the capacity to make vaccine was used, in 6 months they could make enough for 5% of the world's population.