A Yellow Fever certificate is definitely required. You will not be allowed entry into Tanzania without it. Malaria precautions are also strongly advised. Malaria Kills
Zanzibar Health Requirements
The following immunizations are a suggestion: Rabies, Tetanus, Diphtheria, Polio, Cholera, Typhoid, Hepatitis A, Hepatitis B and Meningitis
Make sure to consult your doctor regarding all the immunizations you require for your trip.
If you require certain medication, please bring enough of it as the hospital services are not up to international standards.
Water SafetyDrink bottled water only.
Personal SafetyJust like else-where on the planet, while crime is not a big issue, be aware and do not walk around alone at night.
Make sure to have copies of all your travel documentation and keep your items in a safe at the hotel you stay with. Make sure that you do not leave your personal belongings unattended.