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Two new Ebola drugs dramatically boost survival in a clinical trial

Both treatments rely on infusing patients with antibodies that latch onto the virus and block it from invading cells.

ByKatherine J. WuNOVA NextNOVA Next

A health worker vaccinating a man who was in contact with another individual infected with Ebola in the Democratic Republic of Congo in January 2019. Image Credit: World Bank / Vincent Tremeau

Ebola may no longer be an incurable disease.

Two therapies tested in a clinical trial in the Democratic Republic of Congo appear to dramatically improve survival rates—so much so that both treatments will now be available to all enrolled patients, scientists announced today.

Both treatments rely on transferring antibodies that target the Ebola virus into patients, conferring swift protection. While Ebola typically carries a fatality rate of around 50 percent (and, in the current outbreak, closer to 70 percent), only about 10 percent of patients who began either therapy soon after falling ill succumbed to the disease.

Two other therapies in the trial, which began in November, with less impressive survival rates have been discontinued so that study participants can switch over to better options.

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The findings remain preliminary, and it’s unclear how the drugs will perform outside clinical trials. But the researchers behind the announcement are hopeful that this early success may pave the way to halting the ongoing epidemic in the Democratic Republic of Congo, which has killed nearly 2,000 since it began last summer.

The treatments, called REGN-EB3 and mAb-114, both involve an injection of antibodies that latch onto the exterior of the Ebola virus. This swarming strategy blocks the virus from invading cells, while immune cells are recruited to take down the invader. A similar process underlies a third drug in the trial, ZMapp, which has until now been considered the standard of care in Ebola epidemics. But REGN-EB3 and mAb-114 both outperform their predecessor, as well as a fourth drug called remdesivir.

Across four treatment centers, half the patients taking ZMapp or remdesivir died, while REGN-EB3 and mAb-114 lowered the mortality rate to 29 and 34 percent, respectively. Deaths dwindled further for patients who received therapy soon after they began experiencing symptoms, with about 90 percent of REGN-EB3 and mAb-114 patients surviving, compared to around 65 to 75 percent of those taking the other drugs.

The results came as a complete shock, Sumathi Sivapalasingam, Regeneron’s medical lead on the REGN-EB3 project, told Helen Branswell at STAT News.

The trial’s findings also underscore the urgency for immediate treatment. On average, people arrive at treatment centers about four days after they fall ill, Michael Ryan from the World Health Organization told Sarah Bosely at The Guardian—a delay that not only reduces the chances of survival, but also increases the likelihood that the virus will be transmitted.

There’s no guarantee that the current numbers will hold as a new series of trials begin, now with a renewed focus on comparing the efficacy of REGN-EB3 and mAb-114. But the manufacturers of both drugs have already committed to continued production.


A photo from the 1995 Ebola outbreak in the Democratic Republic of Congo. Image Credit: CDC/ Ethleen Lloyd

It’s unclear why the two new treatments have a leg up over ZMapp, but it may have something to do with how each is formulated. While ZMapp is a slurry of a single antibody isolated from mice infected with Ebola, REGN-EB3 is a mixture of three—an immune cocktail that boosts the body’s chances of keeping the virus in check. mAb-114 also has a single antibody ingredient, but one isolated that was from a human Ebola survivor, reports Megan Molteni at Wired.

Having two options available also makes for an unexpected boon, providing a natural backup in case one drug or the other encounters complications, Ryan told Donald G. McNeil Jr. at The New York Times.

The forecast isn’t yet clear, especially for the now-unseated ZMapp. But potentially taking its place are two new therapies that may finally change the outcomes for Ebola patients.

“From now on, we will no longer say that Ebola is incurable,” Jean-Jacques Muyembe, the director general of the Institut National de Recherche Biomédicale in DRC, which oversaw the trial, told Bosely. “These advances will help save thousands of lives.”

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