There was no real flu season from 2020-2021 because of quarantines, masking, and social distancing, so there was nothing to build off when coming up with the vaccine for 2021-2022. It's always a guess based on what we see evolve from the warmer climates as they transition to cooler climates and the flu makes its way north during the summer/fall but even more so this time. Also an increase in vax skepticism so many didn't get their shot for reasons.