Two years ago, most of the chimpanzees used for medical research in the United States were “retired” and sent to sanctuaries to live out the rest of their lives. Now, the United States National Institutes of Health (NIH) has announced that it is shutting down its chimpanzee medical research program once and for all.

As before, the 50 currently owned primates will be sent to sanctuaries. Another scheme, wherein 82 other chimpanzees are supported by the NIH but owned by other medical research facilities, will also be phased out over time. The director of the NIH, Francis Collins, spoke to Nature about the decision: “I think this is the natural next step of what has been a very thoughtful five-year process of trying to come to terms with the benefits and risks of trying to perform research with these very special animals. We reached a point where in that five years the need for research has essentially shrunk to zero.”

Around 310 chimpanzees were retired in 2013, in line with a recommendation from the Institute of Medicine (IOM). Their report also set the bar extremely high for allowing chimpanzee experiments to take place, with only the most important, vital, time-dependent experiments permitted on the remaining 50. Most of the experiments the IOM accepted as serving the greatest benefit to humans involved research into infectious diseases.

Earlier this year, the U.S. government gave research chimps the same protection rights given to endangered species, meaning that almost all invasive research on them was prohibited. Non-invasive behavioral studies using chimpanzees were allowed to continue, however.

This may seem like a pioneering step, but a ban (or at least, incredibly severe restrictions) on using great apes for medical research is in place in several other countries already, including the Netherlands, New Zealand, Sweden, Germany, Austria and the United Kingdom, the last of which banned this type of research in 1986.

Image credit: The last 50 captive chimpanzees owned by the NIH will be put in sanctuaries. apple2499/Shutterstock

Chimpanzees were used for research as they are genetically and physiologically very similar to humans. Now, other animals will have to be used in their place. It is due to this similarity that many have argued that it is unethical to intentionally harm these primate cousins of ours in the name of medical research.

However, not everyone is happy with this decision. Allyson Bennet, a developmental psychobiologist at the University of Wisconsin-Madison, points out that the sanctuaries do not have the same welfare standards that applied to the NIH-supported centers. Other researchers that require chimpanzees for conservation work – permitted even after the 2013 ruling – aren’t happy either.

Peter Walsh, who was leading an effort to develop an Ebola vaccine for wild chimpanzees using captive specimens at the University of Louisiana, will now find his research has hit a considerable, perhaps permanent, roadblock. “There really is no other place to do conservation-related trials but the US biomed facilities,” Walsh told Nature.