It takes a couple of weeks to reach full effectiveness, but isn't it something like 65-70% chance of not needing hospitalization if you're infected with omicron if you've had all three shots? I swear I saw a source on that in the past few days that put it in that range. It helps a little bit with spread/initial infection, too, but I don't think we have numbers on it yet. Think of it as "flu shot" levels of protection, as opposed to "polio vaccine" levels. It helps, but you're still at risk.

It's early enough that there isn't a ton of hard data yet, and either way, it doesn't look great -- personally, I recommend being a weird shut-in for as long as you can stand. No-contact takeout and delivery are still options at most places; might as well not endanger kitchen staff any more than they already are.

Disclaimer: I'm a weird shut-in. Username is only semi-ironic.

Edit: dug through my browser history and found the link. The booster prevents around 55% to 80% of symptomatic cases:
https://www.bostonglobe.com/2021/12/17/nation/uk-study-finds-no-evidence-omicron-cases-are-less-severe-than-delta/

Having had COVID probably only offers 19% protection against Omicron, the study showed on Friday. That was roughly in line with two doses of vaccine, which the team estimated were as much as 20% effective against Omicron. Adding a booster dose helped dramatically, blocking an estimated 55% to 80% of symptomatic cases.

...

There was no evidence of Omicron cases being less severe than Delta, based on the proportion of people testing positive who had symptoms or went to the hospital, the team said.

Just how severe Omicron cases will be remains unclear. It’s too soon to say how hospitalizations will play out in the UK. In South Africa, which announced the discovery of the variant on Nov. 25, authorities said on Friday the rate of hospitalizations seems to be lower than during the country’s earlier wave of Delta infections.