The Cure

A cure for zombification is a briefly mentioned in Dead Rising 2: Case West and Dead Rising 3.Not much is known about this cure besides that it has been created by Phenotrans. It's current status is unknown.

Dead Rising 2: Case West
Upon defeating Harjit Singh, the mastermind behind the Las Vegas outbreak, Frank West and Chuck Greene find out from Marian Mallon that there is in fact a cure to the zombie virus. Right before the Phenotrans Facility is set to self destruct, making it too late for the cure to be found.It is believed that the cure had been destroyed within the destruction of the Phenotrans Facility.

Dead Rising 3
Mallon is later killed by Gen. John Hemlock for bringing up the cure. Making the status of the cure active but unknown.