SAN DIEGO (CBS Los Angeles) – Nine great apes at the San Diego Zoo have received a COVID-19 vaccine, it was reported Thursday.

The four orangutans and five bonobos received an experimental vaccine developed by drug maker Zoetis, per CBS News.

The zoo chose to give the great apes the vaccine after several gorillas at the San Diego Zoo Safari Park contracted COVID-19 in early January.

“That made us realize that our other apes were at risk,” Nadine Lamberski, chief conservation and wildlife health officer for the San Diego Zoo Wildlife Alliance, told the San Diego Union-Tribune newspaper Thursday. “We wanted to do our best to protect them from this virus because we don’t really know how it’s going to impact them.”

They mark the first known non-human primates to get the shot, according to CBS News.

Zoetis announced in late January that it had received a request from the zoo to provide them with the experimental vaccine for emergency use. Zoetis said it has tested the vaccine on dogs, cats and minks, and so far it has proven to be safe and effective.

A San Diego zoo spokesman told CBS News that the great apes each received two doses of the vaccine over the past several weeks.

This comes after at least two members of the troop of eight western lowland gorillas were infected with the disease in early January, showing symptoms such as congestion, mild coughing and lethargy.

By late January, the animals were eating, drinking and interacting, which seemed to indicate they were on their way to fully recovering.

The San Diego Zoo and its Safari Park reopened to the public on Jan. 30 after being closed for several months due to California’s regional stay-at-home order because of the pandemic.

The nonprofit San Diego Zoo Wildlife Alliance is the parent company for the zoo and the safari park.