Qantas immunisation policy, page-45

In any given year there's about 10 different new influenza strains about, so in a lot of ways it's a more difficult problem.

Covid hasn't really had much time to mutate as wildly, so it's easier to make a focused highly effective vaccine for that one strain than it is for all types, subtypes, lineages, clades and sub-clades of the influenza virus.