According to the Belize Tourism Board:
[ Must continue to present a negative COVID-19 test to enter Belize. Belize will accept a PCR test taken within 96 hours of travel or a rapid antigen test taken within 48 hours of travel. Those who fail to present a test will be required to undergo one upon arrival at the airport at a cost of $50 (payable only in cash). Travelers who test positive for COVID-19 at the airport will be placed under a mandatory 14-day quarantine. ]
[ Need only to present a vaccination record card, with full inoculation completed at least two weeks before their arrival into Belize. ]
Which means, if you're not vaccinated and you take a few days off from your work to enjoy Belize and you test positive when you get there, they can detain you for two weeks in lockup and your job back home is screwed!