I'm not sure why you are all arguing over semantics. @sanityisamyth is correct that the data suggests 2 doses of AZ gives 0% protection against SYMPTOMATIC infection with omicron. 2 doses of Pfizer gives 30% protection. 2 doses of any vaccine plus an mRNA booster gives 70% protection against against SYMPTOMATIC infection with omicron.
assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1040076/Technical_Briefing_31.pdf
There isn't the data yet to know whether 2 doses of AZ gives any protection against severe disease or not. Furthermore, the small sample size used to calculate the vaccine effectiveness and the fact that most people who had AZ are older and, therefore, more likely to be effected severely by COVID, possibly have a less good immune response to vaccination, and probably were vaccinated less recently, could all effect the reliability of the calculations. That said, it's evidence enough that we really do need boosters, especially if you had AZ.
There isn't any data in the report about how much protection a single does of Pfizer provides against omicron so you can't actually conclude that 2 doses of AZ plus Pfizer is any better than one dose of Pfizer against omicron... I would expect that it would be but you can't assume that.
It really doesn't matter though. The overall conclusion should be the same. Get a booster if you want the best protection, especially if you had AZ. I hope everyone on this thread who wants one can get one quickly. Lots of walk in clinics (some pre-bookable) in London are offering boosters to anyone over 18 who was vaccinated over 3 months ago, in case that helps anyone.
Antibiotics and vaccines work very differently so you can't compare the two.