I was told by a UA agent that if transiting through GRU (Sao Paulo, Brazil) you do not need the yellow fever shot. But I don't think I'd take the word of a UA agent. When looking for award tix to JNB from the US with UA miles, UA is showing most availability on their flights to GRU then connecting on to SA flight after a very long 8-9 hour layover.
What if the flight from GRU was canceled and your layover now became >12 hours and you didn't have the shot? Would you have to abort your trip and turn around and go home?
Has anyone ever transited successfully through GRU without the yellow fever shot?