I never got a flu shot, I was not aware that I was implying a time frame here. Point taken

I don’t think it’s fair to frame their intent that way. “Like” does not mean “exactly”. A period of time on the order of years is fine.

It's how I understood it, and I don't think it's even ambiguous. If you say something is like the flu vaccine that implies you're referring to a property that vaccines in general don't have – you would just have said "vaccine" then. See Griece's maxim of quantity. Not lasting infinitely is such a common property.

It's not what they intended, sure, but that the Covid vaccine has to be refreshed every year or so is what I understood and what they actually said.