Oh dear! Time to panic. XEC will simply become the dominant sub-variant of Omicron which in turn will be replaced by another sub-variant. This is the evolutionary process of Omicron.
"The good news is that so far there is no evidence that XEC causes different symptoms or more severe disease than other recent strains—although a COVID infection is always a concern for certain people, including those who are older or immunocompromised."
https://www.yalemedicine.org/news/3-things-to-know-about-xec-the-latest-covid-strain
So just another non severe variant for the vast majority of humans. As for the transmissibility this is how it becomes the dominant variant.