DRC is no stranger to Ebola outbreaks. Why isn’t there a vaccine or treatment to help now?

By Meg Tirrell, CNN

(CNN) — The fast-growing Ebola outbreak in the Democratic Republic of Congo came to the world’s attention only a little more than a week ago and is already the third-largest on record. But it’s the 17th outbreak the country has dealt with since the virus was discovered there in 1976.

Ebola can be fatal in as many as 25% to 90% of people who get infected. Scientists are now racing to develop new potential vaccines and treatments that could help stop this outbreak, but authorities emphasize that, currently, there are none approved. Why?

A less-common virus

The current outbreak is caused by the Bundibugyo strain of Ebola, which was also associated with two previous outbreaks. One in 2012 in the DRC had 38 laboratory-confirmed cases and 13 deaths, and one in 2007 along the DRC-Uganda border had 131 reported cases and 42 deaths.

Ebola infections are much more commonly caused by the Zaire strain, which drove the biggest outbreaks in history: one in 2014 to 2016 in West Africa and another in the DRC from 2018 to 2020. Those killed more than 11,000 and more than 3,000 people, respectively.

A vaccine was developed during the West Africa outbreak and trialed successfully there in 2015. Called Ervebo, it was approved by the US Food and Drug Administration in 2019 and has been cleared in several countries in Europe and Africa.

But that work didn’t extend to other types of Ebola.

Could the existing vaccine be used for this outbreak?

That’s been under consideration, according to Dr. Anne Ancia, the World Health Organization representative in the DRC. But there’s limited information about how well the Zaire-targeted vaccine would protect against the Bundibugyo strain, as well as unknowns about its safety.

“I’m glad I’m not a clinician that has to make that decision,” said Dr. Thomas Geisbert, a professor in the Department of Microbiology and Immunology at the University of Texas Medical Branch who researches interventions for Ebola and similar viruses.

He and others showed in 2011 that a vaccine similar to Ervebo did provide protection against Bundibugyo in monkeys, but it was a small test using just four animals for both ethical and financial reasons, he told CNN.

They gave the monkeys the Zaire-targeted vaccine and 28 days later challenged them with the Bundibugyo virus. Three of four were protected.

“It’s encouraging,” Geisbert said. But models suggest that the Bundibugyo virus can be less lethal than Zaire, and in monkeys, 25% might survive without vaccination. So he estimates that the limited data available suggests the Zaire-targeted vaccine could provide perhaps 50% protection against the Bundibugyo virus, but bigger studies are needed.

And the safety of using this vaccine in the current outbreak is “the $64,000 question. You’re darned if you do and darned if you don’t, right?” Geisbert said.

One concern is that a vaccine that diverts the immune system’s attention to a different type of Ebola could interfere with its response if it was already exposed to Bundibugyo, he said. “You don’t want to make something worse.”

WHO chief scientist Dr. Sylvie Briand said Friday that because it has “very little evidence of cross protection for Bundibugyo,” Ervebo isn’t considered a top choice for a vaccine approach.

Merck, the maker of Ervebo, said it has supplied more than 500,000 doses over the past five years to a global Ebola vaccine stockpile, which it said it would work with UNICEF and the International Coordinating Group on Vaccine Provision to continue to maintain. The company also said it could produce more doses if it’s decided that Ervebo should be deployed in the current outbreak.

What about new vaccines?

Both the Covid-19 pandemic and the 2014 Ebola epidemic in West Africa proved that the world can develop vaccines on expedited timelines in emergencies. That work is underway now, too.

The most promising approach is an experimental vaccine that’s similar to Ervebo but targeted for Bundibugyo, said Dr. Vasee Moorthy, a senior adviser to WHO overseeing a research and development blueprint.

The vaccine delivers a protein from the Ebola virus using another virus – vesicular stomatitis virus – to teach the immune system to recognize it. Geisbert said he’s also shown encouraging results with this approach for Bundibugyo in nonhuman primates, finding that one shot of the experimental vaccine, with a challenge with the virus 28 days later, provided “complete protection; animals don’t even get sick.”

Geisbert also said the vaccine worked in animals as a post-exposure treatment, similar to how the rabies vaccine is used. The problem is that clinical-grade material for testing in humans isn’t yet available and is likely to take six to nine months, Moorthy said in a briefing Wednesday.

“This needs to be prioritized as the most promising Bundibugyo candidate vaccine,” he added.

The nonprofit biomedical research group IAVI, which has worked to advance vaccines using the same recombinant VSV technology for similar viruses, said Wednesday that it’s “prioritizing an investigational rVSV Bundibugyo candidate in the context of the current outbreak” and is working to put together funding.

Merck also said it’s “exploring how we can support response efforts … including potential collaborations with global health and research organizations on research and/or vaccine development.”

Another vaccine is in development using the same technology as the Oxford University/AstraZeneca vaccine for Covid-19, Moorthy said. It could be ramped up faster but has less data supporting it. When used during the Covid-19 pandemic, the vaccine was associated with a rare risk of blood clots; Oxford notes that for a disease such as Ebola, “where up to nine out of 10 people who are infected can die, the very small risk of blood clots is outweighed by the protection which a vaccine may bring.”

Oxford also said the Covid-19 vaccine was estimated to have saved 6 million lives in 2021 alone.

The vaccine uses a different virus, an adenovirus, to deliver genetic instructions to train the immune system to recognize the Ebola virus protein.

Doses could be ready for human clinical trials in as little as two to three months through a collaboration between Oxford and the Serum Institute of India, Moorthy said.

“They are manufacturing that as we speak,” but animal data supporting the vaccine isn’t yet available, he said. Those findings will influence “whether that is considered a promising candidate research vaccine for Bundibugyo.”

Are there any medicines that help?

Trials of therapeutics could start sooner, Moorthy said, because some existing drugs may help against Bundibugyo. “There certainly is hope along the way,” he said last week.

Under consideration are “broad-spectrum approaches that may work across multiple Ebola virus species,” since there are fewer options targeting Bundibugyo specifically, said Dr. Amanda Rojek, an associate professor of health emergencies in the Epidemic Diseases Research Group at Oxford’s Pandemic Sciences Institute.

Those include the antiviral drug remdesivir, made by Gilead Sciences and approved for Covid-19 as Veklury, and a monoclonal antibody cocktail from Mapp Biopharmaceutical called MBP134, she said. One complicated aspect of these medicines is that they’re often given through IV infusion, which can be more difficult logistically in an area that’s challenging to work in, such as Ituri province in the DRC, where the current outbreak is centered.

Geisbert said MBP134 “is probably the one with the best preclinical data right now,” shown in one of his studies to protect monkeys even when given at an advanced stage of illness. It showed protection against Bundibugyo as well as the Zaire and Sudan strains of Ebola.

Antibodies are generated as part of our immune response to invaders like viruses, and MBP134 is a combination of two antibodies from a survivor of the 2014 Ebola outbreak, according to Mapp.

Drugmaker Regeneron also has an approved antibody cocktail for Ebola, called Inmazeb. One of the three antibodies in the combination has shown activity against Bundibugyo but hasn’t been tested in animals or people, a company spokesperson told CNN.

WHO scientists said Friday that the Regeneron antibody and MBP134 are being prioritized for clinical trials. They’re also looking at use of an antiviral drug similar to remdesivir, called obeldesivir, for post-exposure prophylaxis for people considered high-risk contacts of Ebola patients. It has the added benefit of being an oral drug instead of administered by IV.

“This would prevent those contacts, should they have been infected by the virus, [from developing] the disease,” WHO’s Briand said Friday.

Is the US government supporting drug and vaccine development?

Historically, the US has been a major funder of trials during health emergencies, but the Trump administration has pulled back on support for global aid programs. The Biomedical Advanced Research and Development Authority, or BARDA, supported development of Ervebo as well as antibody drugs targeting the Zaire strain. The National Institute of Allergy and Infectious Diseases has been a key supporter of trials, as well.

Mapp received a $14.8 million contract from BARDA in 2018 to start a human clinical trial of MBP134 after animal studies showed that a single dose “demonstrated unprecedented therapeutic efficacy” in nonhuman primates against the Sudan strain of Ebola.

Last week, BARDA coordinated shipment of an experimental antibody treatment for potential use in high-risk Americans exposed to Ebola, a spokesperson for the US Department of Health and Human Services told CNN. HHS didn’t respond to questions about whether the US government would also support clinical trials of medicines in the DRC or development of Bundibugyo-targeted vaccines.

Mapp didn’t respond to questions from CNN about supply of its antibody or plans for a clinical trial, but its president, Larry Zeitlin, told Nature that the company has enough doses for a trial and that the drugs are owned by BARDA.

Regeneron has made its FDA-approved treatment available for free in outbreak zones in the past, the company’s co-founder, president and science chief, Dr. George Yancopoulos, told CNN Friday. He said the company has also supplied tens of thousands of doses to the US government stockpile and is coordinating with HHS to make its triple combination, which contains the antibody with activity against Bundibugyo — called maftovimab — available in this outbreak.

“We are also actively scaling up production of the single antibody maftovimab in case there’s a need for more treatment,” Yancopoulos added.

Why aren’t we more prepared?

Funding for research into viruses like Ebola has been victim of a cycle of “panic and neglect,” Rojek said: “rapid investment during outbreaks followed by loss of momentum afterwards.”

It’s incredibly frustrating to the countries constantly battling Ebola.

“If this outbreak was in Europe or in the US, I can assure you that medicines and vaccines would be available, but we are not there to cry,” Dr. Jean Kaseya, head of the Africa Centres for Disease Control and Prevention, said Saturday. “We need to accelerate with R&D.”

It was a similar situation in 2014, Geisbert said. At that time too, he said, “everybody’s scrambling around.” Work from the early 2000s had shown that the VSV Zaire Ebola vaccine approach “is awesome … but we don’t have a clinical-grade vaccine.”

Merck picked it up “and did the right thing, but it’s still a long process,” Geisbert said.

Still, Rojek argued that in some ways, the world is in a better place than it was a decade ago, with ready surveillance systems, faster diagnostics, established ways of running clinical trials and stronger international coordination. There are major challenges surrounding this outbreak, including its epicenter in conflict-ridden Ituri province and the less common Bundibugyo form of the virus, she said. But “this is not the same situation as 2014.”

And she pointed out there are methods of controlling outbreaks that don’t rely on vaccines and drugs: “rapid diagnosis, isolation, infection prevention, contact tracing, safe clinical care and community trust.”

“Vaccines and therapeutics are extremely valuable additional tools,” she said. “But they are not the only reason outbreaks can be controlled.”

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