Oral Vaccine — Peter Walsh

Oral Vaccination

Vaccine delivery with a hypodermic dart has great potential in research and tourism programs where gorillas and chimpanzees tolerate close approach by humans. However, darting becomes more difficult as habituated apes get wise to veterinarians carrying blow pipes and dart guns. And it’s not a realistic option at all for gorillas and chimps that aren’t habituated to human approach: in other words, the vast majority of wild populations. This leaves two possible alternatives.

In the long term, the best hope may be self-disseminating vaccines, attenuated viruses that cause only very mild infections but that spread readily between individuals. In theory, vaccine introduced to a small number of seed individuals, say by darting, could spread to protect an entire population. In practice, there are a number of substantive technical hurdles involved in engineering a vaccine that will reproduce and transmit readily within the target species without causing serious disease in that species or spreading to other species in which the virus might cause more serious infection. My gut instinct is that these challenges can be overcome. And, eventually, self-disseminating vaccines seem likely to become a primary tool for the control of zoonotic disease emergence. But that’s likely to be decades in the future.

The second option is oral delivery. Several important human vaccines (e.g. oral polio) are now delivered orally. And oral vaccines have long played an important role in the control of both domestic livestock diseases and wildlife diseases, with tens of millions of oral rabies vaccine baits already distributed in Europe and the United States. This long record of safe and effective use in wildlife led me to pursue an oral rabies vaccine as a platform for vaccinating wild apes against Ebola. In particular, Matthias Schnell of Thomas Jefferson University had engineered an attenuated rabies vaccine used extensively in oral vaccination of foxes to include a small segment of Ebola coat protein. So, I asked him to collaborate in a trial on captive chimpanzees. The trial was held at New Iberia, which donated all of its costs.

We delivered the vaccine orally to six chimps and through intramuscular injection to an additional four chimps. Once again, none of the chimps exhibited any clinical, behavioral, or serological symptoms of serious adverse reaction to vaccination. And all of the study chimps subsequently developed robust antibody responses to both Ebola and rabies virus antigen. Sera from vaccinated chimps also neutralized Ebola antigen. To my knowledge, this was the first trial of an oral vaccine in any endangered species.

Captive Chimpanzee Testing Controversy

This oral vaccine trial occurred at the end of a long-running debate about the use of chimpanzees for biomedical testing. The National Institutes of Health had recently announced that it would no longer support biomedical testing on chimps. And the US Fish and Wildlife Service was about to revise guidelines that would ban use of chimpanzees for biomedical testing under the Endangered Species Act. I was then speaking out publicly about the Catch 22 this would create for conservation vaccine development, with African park managers requiring vaccine testing on captive apes but no place where rigorous scientific trials could be performed. This included a one-hour discussion on Irish Radio with chimpanzee goddess Jane Goodall in which I rebutted the scientifically indefensible claims about alternatives to animal testing then being made by Goodall’s collaborators at the Human Society of America. No, computer simulation is not currently a viable alternative to animal testing and won’t be for many, many decades to come. And, no, testing in cell culture will never tell you how an entire mammalian immune system will respond to a vaccine.

Hoping to raise the profile of the conservation issue, I also convinced New Iberia to give access to Miles O’Brien, the science correspondent from PBS’s News Hour. After assuring us that he was focused on a conservation story, O’Brien aired a report that gave equal time to the ban on chimpanzee use in biomedical testing, including re-airing previously reported footage obtained in a Humane Society “sting” operation claiming animal abuse at New Iberia. Press interest aroused by the News Hour piece gave the Humane Society a national platform to recycle misinformation about alternatives to animal testing. O’Brien’s piece also interspersed flattering footage of comparative psychologist Brian Hare playing with bonobos with false and slanderous claims by Hare about the motivations behind the trial, with Hare labeling it a desperate attempt to find new funding sources for the research program at New Iberia. Hare also boldly asserted that ape sanctuaries in Africa could easily host vaccine trials when the Pan African Association, in fact, had a policy explicitly advising member sanctuaries not to do so. Unfortunately, O’Brien didn’t let New Iberia or me directly rebut these spurious claims. In fact, O’Brien didn’t even tell us he was going to air them. Elsewhere, Hare also made baseless claims of how “incredibly risky” and “outrageously expensive” vaccinating wild apes would be: claims I could easily have debunked given that in 2011 had I led a vaccine trial that showed no serious side effects on wild gorillas and was completed on a shoestring budget (see "Measles” section of this website).

Why researchers are racing to test an Ebola vaccine for apes | PBS NewsHour

The Controversial Vaccine That Could Save Apes From Ebola - The Atlantic

Responding to a Public Health Objection to Vaccinating the Great Apes | SpringerLink

The Fish and Wildlife decision to ban biomedical testing on chimpanzees and O’Brien’s News Hour piece effectively ended my vaccination work. In principle, New Iberia could have applied for a conservation exception to the ban. But, in practice, the negative publicity by O’Brien’s piece scared off both potential funders and collaborators with the facilities and the highly trained personnel necessary to do further vaccine trials safely and rigorously enough to be accepted as valid by park managers and conservationists in Africa. In addition, the Ebola epizootic wave had by then moved out of western gorilla range. Gorilla and chimpanzee carcasses were no longer showing up in droves. Out of sight, out of mind. Individual animal rights triumphed over species survival. I reluctantly shelved my vaccination work and moved on.