A recently published study provides details of a series of 8 short-term travelers to the Zanzibar archipelago who contracted malaria. One person died. None of the travelers took anti-malaria medication during their stay in Zanzibar.
A resurgence of malaria has been observed in the Zanzibar archipelago for several years. In addition to optimal mosquito bite prophylaxis, chemoprophylaxis (preventive medication) against malaria is strongly recommended, even for short-term trips!