Remember there's also a 12 week delay between having covid and booster. And that the booster is nowhere near effective enough at preventing omicron infection (70% reduction which is the best it's ever suggested for a short timer is still almost guaranteed if you mix indoors with cases on multiple occasions) I would love to see the actual evidence for 12-15 year old boosters against omicron, given there was reportedly not the evidence for them against Delta where they had >95% effectiveness for 3 months.
On London, whilst it's undoubtedly peaked at the moment, what I would say is there's strong reason to suspect the peak is artificial based on mitigations (test and isolation and individuals cancelling events), That's likely why we've already had 2 peaks, and it seems to me that a third peak after NYE would be expected.
The mass testing alone is a huge mitigation that delays spread - just not much, and not enough to spread out hospital load much, and mostly just increases the days of really high reported cases.