Also, the drug the American dr. received was not his only treatment. He received an injection of blood from a 14 yro Ebola survivor. Since he had two very different treatments, it’s impossible to know what role either one played in his recovery.
After recieving the super duper secret never before tried on humans amazing magical miracle serum, within the hour he was snatched from death's door, his rash gone and had perked up to nearly dancing on his bed.