As Ebola spreads, scientists race to find vaccines and treatments

Health workers disinfect a coffin containing the body of a man presumed to have died of Ebola at a hospital in Mongbwalu, Democratic Republic of Congo, May 25, 2026. As the Ebola outbreak spreads in the Democratic Republic of Congo and Uganda, health workers are rushing to provide supportive care, hoping that some patients will recover on their own, while isolating the sick and tracing contacts of the infected. (Arlette Bashizi/The New York Times)

By CARL ZIMMER

As the Ebola outbreak spreads in Congo and Uganda, health workers are rushing to provide supportive care, hoping that some patients will recover on their own, while isolating the sick and tracing contacts of the infected.

Missing from the fight? Vaccines and drugs that might stop the virus. Dismayed by the scale of the burgeoning epidemic, scientists are scrambling to find them.

On June 1, two major nonprofit vaccine organizations announced tens of millions of dollars of funding to develop vaccines. Experts from the World Health Organization have also recommended testing a handful of monoclonal antibodies and other drugs as potential treatments.

Researchers said that it would take months find out whether these measures work. But the treatments will probably still be valuable at that point, because the outbreak is likely to continue raging.

“It’s going to take a long, committed response to bring this outbreak under control,” said Richard Hatchett, the chief executive of CEPI, a nonprofit that supports the development of vaccines and other pandemic countermeasures.

One reason that Ebola disease is so hard to fight is that it is not caused by a single kind of virus. When scientists refer to “Ebola virus,” they mean a species first discovered in 1976, in what was then Zaire.

Since then, researchers have identified five other species of viruses in the same genus, including one called Bundibugyo virus.

Like Ebola virus, Bundibugyo virus causes Ebola disease — producing symptoms such as sudden fevers, muscle pain and vomiting. The infection can lead to uncontrolled bleeding and rapid organ failure, killing a substantial fraction of patients.

Bundibugyo virus is responsible for the current outbreak of Ebola disease. Before now, it had caused only two small outbreaks since its emergence in 2007.

Most of the outbreaks of Ebola disease over the past 50 years have been caused by Ebola virus. As a result, there are two licensed treatments and one vaccine specifically for it, and nothing specifically for Bundibugyo virus.

These two species of viruses split from a common ancestor long ago — probably millions of years ago — and have been evolving in different directions ever since.

So maybe it’s no surprise that doctors were confused when patients started coming to clinics in Africa with symptoms of Ebola in April. Diagnostic tests were designed to recognize genetic sequences from the more common Ebola virus. Doctors are just now gaining access to tests that can detect Bundibugyo.

Evolution has altered the molecules, known as glycoproteins, that stud the surfaces of these two viruses. Both species use glycoproteins to latch onto cells and slip inside.

When people become infected with either virus, their immune systems start making antibodies that stick to these glycoproteins and block the viruses from infecting cells. If this immune response is strong enough, people can recover from Ebola disease.

To make a vaccine, scientists looked for a way to train the immune system to make those antibodies. Erbevo, the licensed vaccine, consists of a harmless virus, known as VSV, engineered to carry Ebola virus glycoproteins that prompt the production of protective antibodies. In 2014 trials, the vaccine provided 100% protection against Ebola virus.

But experts doubt that it will provide strong protection against the Bundibugyo virus. About a third of the building blocks in Bundibugyo glycoproteins differ from those carried by Ebola virus.

“It’s just different enough on the surface that your immune system finds it to be a different thing,” said Erica Ollmann Saphire, a virus expert at the La Jolla Institute for Immunology in San Diego.

To halt the current outbreak, doctors would need to give people a vaccine proven to work specifically against Bundibugyo virus. That doesn’t yet exist, even though scientists have been researching the species since it was first discovered.

That’s the gap that CEPI is hoping to help fill. The group will offer up to $61 million to prepare three candidate vaccines for clinical trials.

IAVI, a nonprofit organization that develops vaccines, will receive up to $3.2 million for a VSV-based vaccine. The group already has experience in creating these vaccines for other viruses, including Sudan virus, another species that has caused Ebola disease.

Another reason to try this approach is a 2014 study in which scientists tried out a VSV vaccine against Bundibugyo virus on monkeys. It provided 100% protection.

While VSV vaccines have a long track record, they have a downside: Scientists have to grow the carrier viruses to make the vaccines, a process that can take several months.

A second vaccine is being developed at the University of Oxford, based on a different viral vector called an adenovirus. In 2020, the Oxford team used these adenoviruses to create a COVID vaccine manufactured by AstraZeneca, which is estimated to have saved more than 6 million lives in the first year of their use.

The researchers have made vaccines for other pathogens, including Sudan virus. “In essence, we are building on what we have done before,” said Teresa Lambe, who is leading the Bundibugyo effort.

CEPI has awarded Lambe’s team up to $8.6 million to develop an adenovirus vaccine carrying Bundibugyo glycoproteins. The vaccine is already being manufactured by the Serum Institute of India.

Thanks to the institute’s manufacturing capacity and the speed at which adenoviruses grow, the researchers say they could have vaccines ready for clinical trials in humans in one to two months.

But the Oxford researchers have never tested an adenovirus vaccine against Bundibugyo virus in animals before. So they’ll also have to carry out those studies in the months to come.

CEPI is also awarding up to $50 million to Boston-based Moderna to create an mRNA vaccine for Bundibugyo. Moderna produced one of the two authorized mRNA vaccines for COVID during the pandemic.

Gavi, another vaccine nonprofit, also announced Friday that it would provide $40 million to support the manufacture of leading Bundibugyo vaccine candidates.

The world would be better prepared for outbreaks of pathogens such as Bundibugyo if scientists could push forward research when there isn’t a public health emergency raging, Saphire said.

And rather than try to make vaccines and drugs that work only against the pathogen that’s suddenly killing people, researchers could look for treatments that are effective against many related species.

“It’s straightforward to do,” she said. “It just takes leadership, will, and the funding to do clinical studies.”