After these initial prodromal symptoms comes the exanthem phase, which is where a red, blotchy, maculopapular rash spreads in a cephalocaudal progression.
In general, infected people are most contagious starting from the final day of the incubation period through the prodromal and exanthem phase, which roughly works out to be 4 days before to 4 days after the onset of the rash.