Omicron ... timing ...

I admit to being confused over the timing. Omicron hit the news in mid-November but already in the UK they're finding that booster protection against Omicron drops at 10 weeks. How can they possibly know that unless Omicron has been around for longer than we've been led to believe? According to an article by Hannah Seo at popsci.com, the UK health agency making the booster findings said there were some caveats to the data - like there not being many Omicron cases in the UK relative to other variants, and their working with a small and perhaps not representative sample size. It did "confirm" that Omicron is not as severe as Delta, but that it would need to be 90% less severe than Delta for hospitalisations not to reach previous levels. Hmmm. But still how can they know this after the Omicron variant only made the news 6 or so weeks ago?