To clarify, it is NOT cholera but Yellow Fever innoculation which is required if coming from a Yellow Fever area (much of Africa, some parts of South America including Venezuela).
Normally, few if any visitors to Ambergris Caye get any kind of sticks. San Pedro has high health standards. Those coming now, following the hurricane, probably should have their shots (especially tetanus and hep A & B) up to date.
There is malaria present on the mainland, but it is a relatively mild strain, present mostly in remote areas, and it is not chloroquine-resistant, so if your doctor recommends it you can take the old Aralen (brand name) malaria medicine, which is safe and has few if any side effects.
Belize First http://www.turq.com/belizefirst/