Nearly a year and a half after the experimental Ebola drug ZMapp reportedly "saved" the lives of two American aid workers, experts still can't say whether the San Diego-made drug actually works in humans.
Results have yet to be reported from a clinical trial launched last year to test ZMapp's effectiveness. In part, that's because researchers have struggled to find enough Ebola patients to study.
"If we had been able to get started six months earlier, it would have been very simple," said Dr. Clifford Lane with the National Institute of Allergy and Infectious Diseases, one of the U.S. scientists overseeing the international trial.
"There would have been, sadly, plenty of cases."
The trial is designed to give ZMapp to half of the participants, while the other half receives only standard care.
By the time patient enrollment began in Liberia last February, the outbreak was already beginning to subside. In May, the World Health Organization declared Liberia Ebola-free (though sporadic new cases have emerged since then).
With the number of new patients in Liberia dwindling, the trial expanded to Sierra Leone and Guinea. Still, the trial has only been able to recruit about 70 patients so far. The last patient was enrolled over a month ago, when three new Ebola cases were confirmed in Liberia.
Last year's plummeting number of new Ebola cases was good news for the African nations hardest hit by the worst outbreak on record. But Dr. Lane said the situation made it more difficult for scientists to get clear answers about the effectiveness of various experimental treatments.
"The challenge now is, without enough cases to rapidly enroll, you run the risk of not getting a final, robust answer."
UC San Diego Research Ethics Program director Michael Kalichman said the fact that results have so far gone unpublished suggests ZMapp is not a surefire cure, as some hasty news reports initially claimed.
"If it were that effective, people would have jumped right on it," Kalichman said. "Ethically, they would have been responsible for publishing it."
However, Dr. Lane said preliminary results have been encouraging enough to keep the trial open.
Grown in bioengineered tobacco leaves, ZMapp is comprised of three antibodies designed to disarm the Ebola virus. The drug has been shown to be highly effective in Ebola-infected monkeys. Work done at the Scripps Research Institute in La Jolla contributed to the drug's development.
Experts say conducting drug trials for Ebola is more challenging than a typical clinical trial. The only opportunity to recruit patients comes during an outbreak, and designing rigorous and ethical protocols during a crisis can prove difficult.
Withholding a potentially effective treatment may hasten a patient's death. But Dr. Lane says researchers can only know a treatment truly works by maintaing a control group to compare with those who do receive the drug.
"The rules of science don't change because there's an Ebola outbreak," he said.
The control group in ZMapp's trial has not been uniform, though. Some control group patients have been given another experimental drug, favipiravir, while others have not. That could make it harder to explain survival outcomes in each group.
Even with those complex factors in play, the researchers have an obligation to report their results no matter how positive or negative, Kalichman said.
"In any situation where human subjects have agreed to take the risk of participating in a research study, we owe it to them to report the results," he said.
Lane agrees. He doesn't want to wait until the next outbreak to enroll more patients. He said if new cases don't emerge in coming weeks, trial results could be published later this month.
"We're dealing with a setting where hopefully — knock on wood — there won't be many more cases," he said. "Probably at some point in the near future we'll close the study, analyze the data and report the results."
Mapp Biopharmaceutical, the San Diego company that developed ZMapp, declined to comment for this story.
