Zanzibar is not an official Malaria area anymore. It is up to you to take Malaria prophylaxis or not. Do bring Mosquito repellent and drink lots of Tonic water (Mosquitos hate the smell of chinine in the tonic water which your skin somehow gives off). If you drink alcohol, enjoy a gin tonic at sunset (gin also contains chinine = double dose of chinine) – the gin tonic is only to keep the Mosquitos away of course 🙂 In the hotel rooms, you have mosquito nets and staff usually spray the rooms at night when they get your bed ready.
YELLOW FEVER VACCINATION
According to the WHO, a yellow fever vaccination is NOT required for Tanzania or Zanzibar. I have a letter that confirms this, pls email me on email@example.com and I gladly forward the letter to you.
NB: Since the reported cases of Yellow Fever in the DRC, the airport officials are asking lately for the yellow fever vaccination certificate on arrival (depending on which country you are arriving from).