XBB.1.5 has higher binding affinity so sticks to the ACE2 entry receptor better and that may give a spreading advantage. It’s certainly replacing all other strains in the US (running rampant is not the same as replacing). Clearly it has a fitness advantage over other omicron strains. Low frequency in the UK will increase with this fitness advantage.
This is not at all unprecedented. Cast your minds back to Nov 2020 when the Kent Alpha variant replaced Wuhan (which was replaced earlier by the D614 variant) and then Along came Delta.
XBB.1.5 may be more spreadable due to evasion of the pre-existing immunity, or it may be due to more inherent transmissibility. Or some element of both. Certainly studies using vaccine sera show it’s about 10x less susceptible to being neutralised compared to earlier BA.1 omicron. And that in itself might be enough to give it that fitness boost.
Now the good news. It’s inhibited by paxlovid, so treatment options remain in place. It’s not neutralised by Evusheld, so prophylaxis for the immunocompromised may be a challenge. AZ have started a follow-on trial in the UK 🇬🇧 and other countries in immunocompromised patients, comparing two new antibodies from Oxford to Evusheld. I’d want to get onto that trial if eligible. Notably as NICE declined to reimburse Evusheld (£1200 per month on a private prescription).
It’s not doom and gloom. I’ve not watched the video.