US proposes once-a-year Covid shots for most Americans

So I've been wondering when the next booster shots were going to be announced. Seems like right about now is when the previous ones would be starting to lose effectiveness.

Where is the scientific evidence that a once-a-year shot is good enough? Right now the US has six to ten variants in circulation, some increasing, some decreasing, with XBB.1.5 ramping up very fast over the last two months:

https://covid.cdc.gov/covid-data-tracker/#variant-proportion...

You can see that four variants have sequentially traded top place for dominance in the last 3 months. The world has about 30 variants circulating:

https://covariants.org/per-country?region=World

and there are hundreds of subvariants and more mutations happening all the time, in both people and animals. Some people with long covid have been found to be harboring the virus in their intestines, where it has to be mutating. It's mutating in animals as well. We seem to have been incredibly lucky that the few vaccines created so far have remained effective to some extent despite mutations. Covid has so far not been seasonal at all, spreading in both summer and winter. And what about long covid and other long term health effects, are mild infections going to gradually decimate the population of workers? So again, where is the science that says once a year is good enough?