The goal at this point is to use mRNA technology to make both flu and covid vaccines that are broadly effective against most variants of the two virus types. The researchers seem to think that doing so for the flu will actually be more difficult because they think the most likely approach for that is a vaccine that targets most of the main H strains (a vaccine that is effective against h1n42 is equally effective against h1n21, etc. The problem is that there are something like 24 different H strains of flu virus and each has to be targeted individually by any vaccine that will protect against them all.). For the universal covid vaccine the plan at this point is to just target a part of the virus that has proven more stable across all the variants, which is believed to be actually an easier task since it requires developing a vaccine that targets one specific thing. Theoretically no more difficult than how the original covid vaccines targeted the original spike protein.