AFAIK some of the breakthroughs in the delivery mechanisms are relatively new. Some of the companies now making a covid vaccine were talking about running a trial for a flu vaccine in the next few years, but obviously that was far less urgent and all the steps (getting permission, getting participants, actually running the study without "unlimited" money, ...) would take longer.
(mRNA would be a good candidate for a flu vaccines because they are fast to produce, which in theory reduces the amount of guessing needed to make the "right" flu vaccine for the year, but of course a) flu vaccines already are a thing even if sometimes wrong and b) a flu vaccine isn't given as high priority overall)
(mRNA would be a good candidate for a flu vaccines because they are fast to produce, which in theory reduces the amount of guessing needed to make the "right" flu vaccine for the year, but of course a) flu vaccines already are a thing even if sometimes wrong and b) a flu vaccine isn't given as high priority overall)