Scientists are creating vaccinations that prevent people from getting bird flu. If the virus mutates, a new vaccine needs to be made. The vaccine needs to be tested, which can be dangerous. It also takes a long time for scientists to know whether the vaccine works
As most people don't take flu shots because later one you develop the flu plus there are symptoms of the shot so yes the flu is not fully known so that's why it's being changed constantly.
Blending inheritance leads to the averaging out of every characteristic, which as the engineer Fleming Jenkin pointed out, would make natural selection impossible if blending were the mechanism of inheritance.
