There is currently no drug approved to fight Ebola, but WHO has allowed medical professionals to use experimental or untested medications in a last ditch effort to save lives.

One drug, an experimental treatment known as ZMapp, has been used to treat six patients: American health workers Dr. Kent Brantly and Nancy Writebol, a Spanish priest, two African doctors and one African nurse. Brantly and Writebol survived but the Spanish priest did not. The African health care workers are showing signs of improvement, according to the AP.

Still, experts say it’s unclear whether ZMapp — a cocktail of three antibodies that attack the virus – actually helped those who received it. Before Brantly received his dose, the drug had only been tested in monkeys.

“Frankly we do not know if it helped them, made any difference, or even delayed their recovery,” said Dr. Bruce Ribner, director of Emory’s infectious disease unit, where Brantly and Writebol were treated.

Experimental Ebola Drug’s Role in Americans’ Recoveries Remains Unclear

Another drug, an Ebola vaccine developed by the U.S. National Institute for Health, is scheduled to be tested on humans for the first time in September. Another vaccine out of Canada is also expected to be tested, the Associated Press reported