A new study provides strong evidence that the experimental drug given to two American aid workers stricken with Ebola in Africa really works and could make a difference in the current outbreak — if more of it could be produced.
In the study, all 18 monkeys exposed to a lethal dose of Ebola virus survived when given the drug, known as ZMapp, even when the treatment was started five days after infection, when the animals were already sick.
Moreover, the monkeys' symptoms, such as excessive bleeding, rashes and signs of liver toxicity, eventually disappeared. By contrast, all three monkeys in the control group died.
Experts said these were the best monkey results reported to date for any Ebola drug, raising hopes that the drug will work in people.
"I think it strongly supports that concept," Dr. Gary Kobinger, the senior author of the study, said in a telephone news conference Friday, shortly before the paper was published by the journal Nature. Still, Kobinger, a researcher for the Public Health Agency of Canada, cautioned that effectiveness in monkeys was not "proof" that a drug would work in people.
The problem is that the supply of ZMapp is exhausted, according to Mapp Biopharmaceutical, the nine-person San Diego company that is developing the drug. And it is expected to take months to make more of the drug, which is produced in genetically engineered tobacco plants.
ZMapp came to the world's attention this month when it appeared to help two American aid workers stricken in Liberia and later flown to Emory University Hospital in Atlanta. The workers, Dr. Kent Brantly and Nancy Writebol, recovered and were discharged last week.
Doctors say it is impossible to say what role ZMapp played in their recovery.
Some other experimental drugs have shown the ability to protect monkeys from Ebola if given shortly after infection, up to about two days. That might make such a drug useful for what is called postexposure prophylaxis — for example, after a person is stuck by an infected needle. But in an outbreak like the one in Africa, most people do not know they are infected until symptoms develop. Hence it would be important that a drug could work even if treatment starts after symptoms appear, as was the case in this study.