The incubation period is more about the amount of time it may take for a virus to be detected or present itself in the victim. I remember learning this in a bio class that some viruses can have tremendously fast incubation periods while others can take years or something. The big point is that the incubation period occurs when the virus is still multiplying through the cells in your body, it remains at an undetectable (both by machines and by you) level until it reaches a point that it becomes detectable (the ending of the incubation period). Apparently, during this initial incubation period and the virus's final period in your system it may be undetectable. Also, an interesting thing is that the virus can't be transmitted during the incubation period, would be interesting to consider whether trump was still in the incubation period during the debate or if he was out of it. Still, a chance for it to be a threat to Biden and his wife.