It would be nice, and seemingly feasible, if they could compare to recent Delta infections (or even current one, seeing as both variants are present right now). Presumably any kind of acquired immunity is more comparable to 3 months ago vs. 21 months ago.

It could still be that among people infected with Omicron, there is a larger proportion of vaccinated people, due to vaccines being less efficient, but that's still a better yardstick.