Visitors to Zanzibar are no longer required by law to have a Yellow Fever vaccination certificate. When you enter the country, please see your local doctor or Travel Clinic for further information about inoculations required for the area.
Malaria is still prevalent in East Africa and so one should also take a malaria prophylaxis. There are many different kinds of medications for Malaria. However, precautions should be taken to avoid being bitten by mosquitos. Apply insect repellent and sleep under mosquito nets at night. Wear long-sleeved shirts and trousers in the evenings.
Zanzibar is not much infected by HIV/AIDS. However, you are advised to avoid all AIDS fueling factors.
As in almost all African countries, it is pleased to drink bottled water and avoid uncooked foods that may have been washed in untreated water. Sunstroke and heat exhaustion are common, so drink sufficient water, wear sensible clothing and use a high-factor sunscreen.
Zanzibar is a safe country, and most locals are friendly and honest. Though simple precautions should be taken so as to have a relaxing and interesting stay in one of the most beautiful places on earth.