Before visiting South Africa, my step-mother, a friend, and I will be visiting Victoria Falls late this August. My understanding is that if there is a Zambian stamp on the passport, the tourist will not be let into South Africa without a Yellow Fever certificate. But the risk in Zambia in general is very low (particularly during the dry season), and the risk near Victoria Falls is non-existent. While not a major problem for me, my step-mother is 82 years old and the risk of receiving a live vaccine is not entirely inconsequential. And my friend with whom we'll be traveling lives in a rural area where getting a Yellow Fever vaccine is extremely difficult (they come in multi-use vials, and no one wants to stock it since it will go to waste if only one or two persons buys a dose from the vial). Will they accept letters from the traveler's doctor stating that the risk of the vaccine exceeds the potential benefit?