In February 2011, a team of scientists led by Peter Walsh at the University of Cambridge injected six captive chimpanzees with an experimental vaccine against the deadly Ebola virus. At first glance, the study looked like a lot of other medical research, in which drugs that are meant for humans are first tested on other animals. But this was different. These scientists were working with chimps to help chimps.

The twin threats of poaching and habitat loss are driving the African apes—chimps, bonobos, and gorillas—towards extinction. Diseases are also a problem. Our ape relatives are vulnerable to infections like anthrax, malaria, and respiratory viruses that spill over from human tourists and researchers.

They can also get Ebola. Under a microscope, the Ebola virus looks like a malevolent knot. In the body of a human or ape, it causes severe and fast-burning disease. In 2006, Walsh’s team estimated that recent Ebola outbreaks have killed around a third of the world’s gorilla population—some 5,000 animals in the Republic of the Congo—and a slightly smaller proportion of the world’s wild chimps.

For years, Walsh has argued that we should protect the survivors with vaccines. He certainly has plenty to choose from: scientists have developed several potential Ebola vaccines that have protected mice and monkeys against the virus. They’re still years away from passing human trials, and since Ebola is a rare disease that mostly affects poor people in the tropics, a human vaccine may never become a commercial reality. These orphaned medicines could be used to save wild animals.

Not everyone agrees. Historically, conservationists have been happy to protect a species’ habitat or to fight poaching, but they’ve railed against interfering with the animals directly. In 1966, Jane Goodall stopped a polio epidemic among Tanzanian chimps by hiding an oral polio vaccine in bananas. “There was a backlash against her,” says Walsh. “It’s very difficult to get anybody to agree to do vaccinations.” But this attitude is waning, as the threat of diseases is becoming clearer. Walsh thinks there’s now more appetite for vaccinating wild animals.

View Images Ebola virus. Credit: Dr. Frederick Murphy, CDC.

In 2011, his team, led by Kelly Warfield, finally tested an Ebola vaccine on three chimps. They used one that doesn’t contain any live viruses; instead, it comprises a piece of the virus’s coat. It trains the immune system to create antibodies that recognise Ebola, without risking an actual infection.

None of the vaccinated chimps showed any signs of weight loss or disease, and they all had similar numbers of blood cells to three chimps that weren’t vaccinated. As planned, they developed antibodies against Ebola. And when the team injected these antibodies into mice, the rodents were twice as likely to survive an encounter with the virus.

That’s not surprising, since the same vaccine has protected monkeys in earlier experiments, says Nancy Sullivan from the National Institute for Allergy and Infectious Diseases, who has worked on Ebola. “It’s a good first step, but whether the vaccine will protect chimps or not, we don’t know,” she says. After all, the team didn’t actually challenge the chimps with Ebola itself. Walsh thinks this is unnecessary. Based on the monkey data and the mouse experiment, he says the vaccine is ready for use.

This study, in which scientists tested a vaccine on captive chimps to protect wild chimps, rather than humans, is the first of its kind. It may also be the last study of its kind.

The era of biomedical research on chimpanzees is drawing to a close. The United States and Gabon are the only countries that still allow this kind of research, and the US may soon leave this short list. In 2011, the Institute of Medicine issued a report saying that “most current use of chimpanzees in biomedical research is unnecessary”—a conclusion that the National Institutes of Health took seriously. In 2013, it announced that all but 50 of its chimps would be retired to sanctuaries. Meanwhile, the US Fish and Wildlife Service has tabled a proposal to list captive chimps under the Endangered Species Act—a move that would ban medical procedures beyond those that “enhance the propagation or survival of the affected species”.

Walsh’s study might still fit the bill but it wouldn’t matter, since labs with the right facilities to house and work with chimps would shut down. That’s a problem, since national park managers in Africa insist that scientists prove the safety of vaccines in captive apes before using them on wild ones (and monkey data won’t suffice). To Walsh, you need captive chimps to test vaccines that would save wild ones from diseases.

He’s not just talking about Ebola, either. Vaccines could also protect chimps from HRSV—a human virus that they catch from humans, often with fatal results. One HRSV vaccine, developed for our own use, didn’t work well in humans but was great at protecting chimps. Beatrice Hahn at the University of Pennsylvania is also developing a vaccine against simian immunodeficiency virus (SIV), which causes an AIDS-like disease in chimps. (Hahn was unavailable for comment due to travel.)

To continue research on such vaccines , Walsh thinks the US Government should keep a humanely housed population of a few dozen chimps specifically for conservation research. “Potentially preventing the extinction of wild chimps should weigh more heavily on the ethical scale than the discomfiture of chimps in captivity,” he says. “They’re not being vivisected or challenged with Ebola. The nasty bit is that, for a couple of months, they’re in a small isolation cage. I don’t like that. It’s not a good thing, but it’s not horrific. I think it’s worth it for the survival of the species.”

John VandeBerg from the Texas Biomedical Research Institute voices similar views in a New York Times op-ed, published last year. “The NIH has not permitted a single chimpanzee that it owns or supports to be enrolled in a new research study since December 2011,” he wrote. “Humans — and chimpanzees and gorillas — may continue to die from diseases that could have been prevented or treated by medical products developed from research with chimpanzees.”

“That is totally silly,” says Brian Hare from Duke University, who does non-invasive research with chimps in African sanctuaries. “They could work with the Pan-African Sanctuary Alliance, because there are more than 1,000 captive chimps in Africa that could be protected.” Kathleen Conlee from the Humane Society of the United States, an advocacy group, agrees. “We don’t need to keep chimpanzees in laboratories for such efforts and could instead work with sanctuaries in Africa, where the chimpanzees actually have a chance of exposure to the virus,” she says, echoing points she made in response to VandeBerg’s op-ed.

But Walsh counters that zoos and sanctuaries don’t offer the controlled conditions necessary for a proper vaccine trial—hence, the need for private facilities.

“Protecting endangered chimpanzees and gorillas against Ebola is certainly a very important topic,” says Tom Geisbert from the University of Texas Medical Branch. But he says that the vaccine Walsh used needs three doses to trigger a protective immune response, which is neither practical nor feasible for wild apes. Instead, the team should check the safety of other vaccines based on weakened viruses, which work after a single injection.

Hare adds that vaccinating wild animals is very tricky. “No tested or proven method that doesn’t cost insane amounts and have extreme risk for wild animals,” he says.

But Walsh argues that it’s easier to vaccinate wild animals than critics think. His field team in Africa have already vaccinated wild gorillas against measles using blow darts, in a trial whose results are not yet published. “It’s not trivial, but it’s not that hard,” he says. In the future, he hopes to develop bait methods that can deliver oral doses of a vaccine without the need for darts. “Again, we need a captive population to test the bait system.”