If you are coming e.g. directly from Europe there is no need for producing the vaccination card. However, if you have been on transit in one of the neighboring countries for more than 12 hours, or you have been out of the airport during the transit period, the vaccination card showing valid yellow fever vaccination must be shown at the entry point.
A statement issued by the Revolutionary Government of Zanzibar informs the public that all guests/visitors travelling from the Tanzania mainland to Zanzibar will not be required to show their yellow fewer vaccination card as Zanzibar is inside the United Republic of Tanzania.