Turns out Omicron may outcompete delta to a greater degree depending on your existing immunity. So an immune naive person is less likely to catch it than someone who's had Corona, who's less likely to catch it than someone who's had one jab, who's less likely to catch it than a triple jabberee. Hence this wave of sickness in the vaccinated.
Dear Vaccinated, thank you for your service in making Omicron the dominant variant! These vaccines had to be useful for something, encouraging the spread and development of new variants, just not what they were designed for.