Looks like three months of enhanced immunity may be about all we can count on from a booster shot. That is, in this UK study of the Pfizer vaccine, “By three months, the booster reduces the risk of a symptomatic infection only by about 50%.” To which I say: remember, everything is additive. So add in a good mask, and good fresh air ventilation, and some air purification, then your risk will be much less.
NPR.org - Covid Booster Omicron Efficacy - January 19, 2022
And according to the NFL (which I trust due to their extensive monitoring), it’s about the same three month period of relative immunity after having had the Omicron version of covid-19. That is, they exempt players from frequent testing for 90 days after their infection.
ESPN.com - NFL Halts Daily Covid-19 Testing Unvaccinated Players Memo Says - January 21, 2022