In August 1976, a 44-year-old headmaster named Mabalo Lokela arrived back in the town of Yambuku in the Democratic Republic of the Congo, after two weeks spent touring with a local mission. A few days after his return, he checked into the local hospital with nosebleeds, dysentery, and a fever. The doctors treated him for malaria, but to no avail. Lokela got worse. In early September, two weeks after his first symptoms, he died. And meanwhile, other people who had come into contact with him started getting sick.

Over the next three months, 318 people became infected, and 280 of them died. That outbreak, and another that took place simultaneously in South Sudan, alerted the world to the existence of a lethal new disease, which eventually took the name of the waterway on which Yambuku is situated—the Ebola River.

Ebola is famously deadly, but not inevitably so. Around 12 percent of those who were infected in the Yambuku outbreak survived their brush with the disease, and many of them are still around today. They’ve lived through seven more documented Ebola outbreaks in the DRC, the latest of which took place this May, less than 350 kilometers away from Yambuku. They’ve watched from afar as the biggest Ebola outbreak in history ravaged West Africa.

Compared to that epidemic, “the DRC’s outbreaks have been smaller and more isolated,” says Anne Rimoin at the University of California, Los Angeles, “and so too have these survivors. They’ve had no contact or follow-up.” They still bear the scars and social stigma of their experience with the virus. But they also carry defenses against it.

Rimoin has shown that the original survivors’ blood still contains antibodies against Ebola. In some cases, people had antibodies that can destroy the virus outright, even after 41 years. “They should be immune to Ebola,” Rimoin says.

Simply finding the survivors was a Herculean task. Medical records from that 1976 outbreak were nowhere to be found, so Rimoin had to ask the researchers who were on the scene to rummage through their files. Once she had a list, her team took several trips to Yambuku to search for the people behind the names. And since the town is so remote, every trip involved a chartered flight and a grueling drive. “It took maybe 9 hours in the dry season, and 20 hours in the rainy season,” Rimoin says.

The team eventually tracked down 14 survivors who, according to Rimoin, were eager to take part in a new study. “They were very happy that there were people out there interested in hearing their stories and understanding what they had been through,” she says. “It may have been a long time ago, but they are still living the consequences of what they’ve suffered. Most of them lost family members. And when they emerged from the hospital, having narrowly survived a terrifying near-death experience, they found their homes had been burned to the ground for fear of contamination. Everything they owned had disappeared.”

Even now, they have to live with the social stigma of having once had Ebola four decades ago. Such is the fear surrounding the virus that the hospital in Yambuku was initially reluctant to let Rimoin bring her volunteers in to take blood samples. “To this day, if you say you’re an Ebola survivor, people will recoil,” she says.

Previously, another team found that Ebola patients retain some immunity against the virus after 14 years, but Rimoin’s team have shown that this protection extends for decades more. All of the 14 people they studied still carry antibodies that recognize at least one of the Ebola virus’s proteins, and four had antibodies that could completely neutralize the virus. “Those are the kinds of responses you’d like to see in a vaccine—long-lasting and robust,” says Rimoin, “which means that these antibodies are of great value to science.”

It’s clear that the Ebola virus can stick around long after symptoms abate, by hiding out in unusual places like eyeballs. One man still carried the virus in his semen 565 days after he recovered. Ebola’s tenacity might explain why survivors continue to produce antibodies against it, long after they’ve finally cleared it from their bodies.

“It’s well-documented that acute viral infections such as measles and smallpox provide lifelong immunity,” says Mohan Natesan from the U.S. Army Medical Research Institute for Infectious Diseases. Ebola infections can clearly lead to similarly long-lasting antibodies, but “it is difficult to predict whether these antibodies will protect from reinfections, or infection with another Ebola species. Further studies with these survivors are warranted to answer these questions."

It’s also hard to say why four of the 14 people developed such potent antibodies. They might have had naturally powerful immune systems. They might have already been exposed to similar viruses in the past, and confronted Ebola with partial immunity. It’s hard to say why with such a small group, but “it is remarkable that 14 suspected survivors were tracked and found in the first place,” says Lauren Cowley from Harvard University. “The 1976 outbreak was much smaller than the recent West African outbreak so a much larger pool of survivors will now be available for future studies on the long-term effects of Ebola.”

Rimoin is now planning more trips to the DRC to continue studying the survivors, including those who made it through later epidemics. She’s on the clock: The average life expectancy in the DRC is 62 years for women and 58 years for men. Many people who were teenagers during the first epidemic are now nearing the end of their lives. Indeed, Rimoin originally identified 16 survivors from the 1976 outbreak, but two of them died before she got a chance to take their blood. “The aperture for studying these people is closing,” she says.