An Ebola vaccine trial yields promising results for protecting wild primates

Following the 2014 West African Ebola Outbreak, scientists have been working to develop ways to treat the deadly illness in order to slow down or outright prevent the next outbreak from occurring. While these treatments are often tested on animals, a group of scientists have been working to create an Ebola vaccine to protect primates in the wild. While the initial results are promising, regulatory changes and attitudes towards medical research conducted on primates could prevent further tests.

Last year, a new Ebola vaccine trial conducted in Guinea and Sierra Leone was found to be enormously effective. But it’s not just humans that suffer from Ebola. The disease poses a very real threat to primates. In November and December 1994, scientists discovered that an entire community of wild chimpanzees living in the Taï National Park in Côte d'Ivoire had vanished. Scientists autopsied the bodies that they recovered, and discovered that the animals had been infected with a new strain of the Ebola virus. In 2011, another study warned Ebola was responsible for killing “roughly one third of the world's gorilla population and only a slightly smaller proportion of the world's chimpanzees.” With primate populations suffering from habitat loss and poaching, the spread of disease can further endanger these animals.

To that end, scientists have worked to create a vaccine that could be used to help protect wild primates. In a study published last week in Scientific Results, researchers found that a new oral vaccine trial “provoked robust immune responses,” in the ten captive chimpanzees involved in the study.

The team specifically wanted to see if the vaccine would work if delivered orally, noting that it’s an established, effective vaccine delivery method used to protect wild populations from diseases such as rabies. Rather than tracking down wild animals to vaccinate them — a difficult prospect for African primates — officials could simply lace bait with the vaccine and wait for the animals to ingest it.

The researchers tested a rabies-derived Ebola vaccine called filorab1, which has been found to be effective in primates. The vaccine is an inactivated rabies virus with an Ebola gene inserted. The chimpanzees were given the vaccine — six orally, four with injections — and had their blood drawn over the course of 28 days. The team found that the vaccine offered a similar level of protection as with prior trials of filorab1, with “robust immune responses” during the first 28 days of the trial, with projections indicating that they were well on their way towards the full immunity that was found in other subjects.

The trial did face challenges, however. In June 2015, the US Fish and Wildlife service listed Chimpanzees under the Endangered Species Act, which truncated the study. As a result, the researchers were only able to draw blood for 28 days, and could not include an “Ebola challenge”, where the animals are infected with the virus to see if the vaccine prevented infection. The study’s authors noted that research benefiting primates is exempt from the new regulations, but due to the changes, “all of the biomedical facilities that held chimpanzees have or are in the process of ‘retiring’ their populations to sanctuaries,” which tend to limit these types of studies. New Scientist points out that until conservation experts and health officials come up with a plan, the vaccine might never be deployed to the wild.