You just demonstrated some extreme ignorance. Apples to pomegranites comparison, the only less-informed comparison I've seen is covid vs. HIV.

1) "The flu" is actually a family of similar viruses, not one single bug.

2) The "flu shot" is actually a cocktail of 3-4 different vaccines, which are selected twice each year based on which (of many available) strains of flu they guesstimate are *most* likely to be *most* prevalent in the coming season. It is never intended, nor would it ever be able, to prevent all flu. It's intended to reduce the impact on society, and improve your individual odds. The bonus is that if you get the shot annually, it improves your odds against strains which are not included in the current shot, because you have some immunity left for strains from years past, which may still circle around.

3) The flu mutates rapidly in a fast cycle which occurs in a unique "reservoir animal" ecosystem of pigs, domestic birds, and peasants in Asia. By bouncing back and forth between species (with vast numbers of animal hosts), it's afforded a tremendous opportunity to mutate. After which it it jumps to people and makes it's way around the world.

4) Many flu strains have been circulating for years, and they have vaccines on the shelf for those. When a new robust mutation pops up, they have to make a NEW vaccine within months to get it into the next cycle's flu shot cocktail. They actually have that down to a science.

Covid has not shown any indication of getting into domestic livestock in a manner such that it can readily jump back and forth between livestock and humans. Once covid is beaten back into a dark corner it will have vastly reduced mutation opportunities.

A covid vaccine is a lot more straight-forward.