Why would I get a flu shot that won't work against the worst strain of flu? Better to stay out of places where flu spreads, if possible.
If you have a child in school, like me, then you probably already have the flu.
Even if the vaccine does not completely prevent the particular strain of flu that is circulating, the antibodies it causes your body to produce can still provide some protection. That means you might still get sick, but the disease will not be as severe. And that difference in disease severity can make the difference between life and death.
The absolute worst case scenario as far as flu goes is when a strain starts circulating that most people have never encountered. Then, they have no residual immunity to it. That is when the flu is most deadly. That's what happened in 1918.