simple - we have vaccines for the seasonal flu.
the reason that this pandemic is so deadly, despite the low death rate (in comparison with with world epedemics) is that carriers often have no symptoms. It spreads around completely undetected in a large percentage of the population and before you know it, everyone has it and the health system is struggling to look after those with more severe reactions.
Whereas other epidemics have very noticable symptoms, so the infected are quickly identified and isolated, and life goes on.
I'm pretty sure i've seen others explain this to you before. Its not that hard to grasp.