The flu is understood to be different, seasonal, yearly variants. It’s also why at least in the US it’s characterized as the “flu shot” as opposed to the flu “vaccine”.
Vaccines like MMR and others are understood to be generally preventative and rarely need booster if after initial doses.
Think about things that generally require boosters…they are almost always referred to by the laymen as “shots”. Nobody calls the tetnus shot a tetnus “vaccine”.
I get what you're saying, and it makes sense, but people also often say "shots" when referring to childhood vaccines (ex: "did they get their shots yet?") They also say things like "rabies shots" and "diptet shot."
And coronavirus is also understood to be seasonal.
However, in spite of all that, I agree that the official messaging throughout this pandemic has been so inconsistent - from masking to "two weeks to flatten the curve" to "boosters" - that the public does have a right to be skeptical and exhausted.
Vaccines like MMR and others are understood to be generally preventative and rarely need booster if after initial doses.
Think about things that generally require boosters…they are almost always referred to by the laymen as “shots”. Nobody calls the tetnus shot a tetnus “vaccine”.