Early data shows some protection against Omicron with previous infection but not a lot, vaccination alone seems to be better and previous variant infection and vaccination even better. There are so many variables within individuals as well. Omicron is going to spread very quickly with short doubling times. Cross fingers this doesn't end with serious disease for any percentage of the population. This could be more of an economic disrupter than serious hospital strain if large swaths of our population is at home on quarantine for 10 days at a time (even with mild illness). Outpatient clinics are going to potentially get overwhelmed.
There are only preprint in vitro studies for immune protection as well and the media is going to FUBAR the results and get everyone in a panic regardless if needed. Horse is out of the barn now. Best thing to do is get immunized, get boosted if due and stay healthy.
Oh, and there is some concern Omicron is mutated enough to avoid certain PCR testing because the genetic markers PCR test for have changed. Rapid testing could be more accurate in some situations. Strange times.