Has this person not had experience treating rabies?
Rabies has a relatively long time from exposure to become symptomatic, because the virus travels through your nervous system to infect your brain. It can be weeks or months from the time you’re exposed until you show symptoms, but once you do it’s nearly guaranteed to be fatal. That’s why standard procedure (in the US at least) is to give the vaccine after exposure, because your body usually has enough time to create antibodies before the virus progresses to the brain.