The 1918 influenza epidemic infected half a billion people out of global population of 1.8 billion. Somewhere from fifty to one hundred million of those people died. Nearly everyone killed by the flu was under 65, with most being between 20 and 40, in whom the body’s immune system’s reaction was so severe that lung tissue was reduced to a thick mass and the victims drowned in their own phlegm. A perfectly healthy young person could fall sick in the morning and be dead that night, as a strong immune system made the disease all the more deadly.
There was no flu shot in 1918, which means people in 1918 were just as vulnerable as people who didn’t get the shot this year. Fortunately the flu this year is vastly less deadly, and will probably only kill a few tens of thousands world wide. It’s a roll of the dice every year, but at some point a flu virus will evolve that drops people like flies. Could be next year, could be in a hundred years. If you get the shot you lessen the odds of dying a rather quick and ghastly death. It’s up to you.