it depends on who you ask, the CDC says 60% fully vaxxed (either the single shot or the 2 shots) and 15% are additionally boosted. 200mm and 50mm, respectively.

Not sure about global statistics but some sites say up to 30% of populations have boosters.

the manufacturers originally said 1 year, but that slowly backslid to news reports of "shots 3 times a year". For all the talk of "boosting for variants" the latest boosters are for omicron. The claim is that this also may help with XBB and kraken and the 2 headed dog variant (not cerebus, but the brother of cerebus: Orthrus).

So to tl;dr it: between 4 and 9 months. But the variants are coming about as often if not more often.