(CNN) ZMapp, an experimental drug that doctors thought may have helped save lives in recent high-profile Ebola cases, may not have been the key factor in survival, a new study says.
The Ebola epidemic killed more than 11,000 people and made more than 28,000 sick between 2014 and 2016.
The drug, considered "most promising," was still in the testing phases at the time. But because it was an emergency, doctors got special permission to use it on their patients, including some treated in the United States.
The drug had showed real promise in tests on primates, but it hadn't been fully tested on humans. Many of the infected people who got it did recover, but even at the time, doctors weren't able to tell whether it was ZMapp that helped them survive while thousands of others died.
Now, according to a study in the latest edition of the New England Journal of Medicine, the results of a randomized controlled trial may come as a surprise to some.
Researchers tested the drug in 72 people from Africa and the United States who had Ebola infections. They found that although it was beneficial overall, ZMapp "did not meet the prespecified statistical threshold for efficacy."
The good news is that there were no major safety concerns identified with use of the drug. Twenty-two percent of patients treated with ZMapp, in addition to standard supportive measures died, compared with 37% of patients who received standard treatment without ZMapp. So the drug was not a game-changer, at least in this particular epidemic.
One of the challenges of this study, though, was that the research was going on during the epidemic. Conditions were not ideal, and that may have affected the results.
Researchers couldn't control all the variables. For instance, although the patients were symptomatic for a few days before getting the drug, in reality, it was likely they had been infected about a week before. That delay could have lessened the impact of the ZMapp treatment.
When the drug was tested in primates, it worked best within five days of infection. In that amount of time, ZMapp had a 90% or greater survival rate.
In addition, seven of the eight people who died in the human trial did so before they were given the second of three planned infusions. That means there may not have been enough of the drug in their system to fight the infection.
More research will need to be done on ZMapp and to see what does work against Ebola infections, but the authors conclude that there may be other drugs that should be considered for experimental use if another epidemic were to occur.