Despite the new efforts, supplies of the drug are expected to be limited to hundreds or thousands of treatment courses by early next year, which would not be nearly enough if the epidemic continues to spiral out of control.

“The biology just doesn’t allow you to do it tomorrow,” said Alan Magill, who heads the malaria program at the Gates Foundation and is trying to arrange for more ZMapp production.

ZMapp was able to protect monkeys from Ebola even when administered five days after infection. And it may have helped a few people infected during the current outbreak, including two American aid workers who got Ebola in Liberia and recovered at Emory University Hospital in Atlanta.

Still, there was only enough ZMapp for seven patients, two of whom subsequently died.

Experts say it is impossible to tell from such limited experience how well ZMapp works. And there are other experimental drugs that have shown promise in animal testing, and production of those might also be increased.

But for now, ZMapp may offer the best shot because it consists of proteins called monoclonal antibodies, widely used as drugs in the biotechnology industry, which latch onto the virus and neutralize it. “It’s extremely rational that an antibody against Ebola would be effective,” said Dr. Susan Desmond-Hellmann, chief executive of the Gates Foundation and a former biotechnology industry executive. “It is extremely rational that it would be safe.”