Fourteen survivors from the first known Ebola outbreak in 1976 appear to have developed immunity against the disease, according to a study published this week in the Journal of Infectious Diseases. The study showed that the survivors blood contains antibodies that protect against, and in some cases even destroy, the Ebola virus.

An earlier study had shown that Ebola survivors have some immunity after 14 years, but this new study shows that protection lasts for at least 40 years. The Ebola virus is known for hanging around longer than anyone would like, frequently hibernating in eyes and semen. This “tenacity might explain why survivors continue to produce antibodies against it, long after they’ve finally cleared it from their bodies.”

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.”