Four orangutans and five bonobos have each been given two doses of the vaccine.

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gorilla portrait
Brent Stirton, Getty Images for National Geographic
| Credit: Brent Stirton / Getty Images for National Geographic

A troop of great apes made history last month as the first known non-human primates to receive a COVID-19 vaccine in the United States.

In February, four orangutans and five bonobos at the San Diego Zoo each received two doses of an experimental COVID-19 vaccine designed for animals, Nadine Lamberski, the chief conservation and wildlife health officer at the San Diego Zoo Wildlife Alliance, told National Geographic.

The apes were given a vaccine developed by the veterinary pharmaceutical company Zoetis. The vaccine was initially developed for dogs and cats.

While the vaccine—which is not built for, tested in, or suitable for use in humans—had only been tested on dogs and cats, Lamberski believed it was worth the risk to use the vaccine on the apes.

The decision to acquire the vaccine came one month after a troop of eight gorillas at the San Diego Zoo Safari Park tested positive for COVID-19, becoming the first great apes in the world to contract the virus.

"This isn't the norm. In my career, I haven't had access to an experimental vaccine this early in the process and haven't had such an overwhelming desire to want to use one," Laberski said.

Healthy again and back on public display, two members of the gorilla troop relax in their habitat. Lamberski’s team plans to give them the experimental vaccine later this spring.
Credit: Brent Stirton, Getty Images for National Geographic

According to Lamberski, the nine apes given the vaccine are doing well.

An orangutan and a bonobo will soon be tested to see whether they developed antibodies, which would indicate that the vaccine is working.

The zoo also plans to give three of its leftover doses to two bonobos and one of the zoo's gorillas who didn't test positive for COVID-19.

A spokesperson for Zoetis told National Geographic that other U.S. zoos are interested in doses of the vaccine for their great apes. The company expects to have more availability by June.

Mahesh Kumar, senior vice president of global biologics at Zoetis, said it remains unclear whether the vaccine is enough to prevent infection successfully.

Cats and dogs showed significant immune responses to the vaccine in the trials, but further studies are needed.

Lamberski said the zoo is considering eventually vaccinating its big cats as well.

For more on this story, visit National Geographic's coverage at on their website.

This story originally appeared on people.com