PORTLAND, Ore. – Three West Coast zoos are taking part in an emergency vaccine trial to protect California condors from a virus that killed over 20 of these birds last spring.

Results from the clinical trial indicate that 60% of the condors who received the vaccine produced measurable antibodies, offering some protection against highly pathogenic avian influenza (HPAI).

The U.S. Fish and Wildlife Service, along with the Oregon Zoo, Los Angeles Zoo & Botanical Gardens and San Diego Zoo Wildlife Alliance, conducted the first-of-its-kind trial for wild birds in the U.S. These three zoos have been long-time partners in the federal California Condor Recovery Program.

"The importance of finding a vaccine that’s effective in protecting California condors cannot be overstated," said Dr. Carlos Sanchez, director of animal health at the Oregon Zoo. "This is a species that not long ago was on the very brink of extinction. Just over 300 individuals exist in the wild — and this year, in a matter of weeks, HPAI wiped out 21 of them. If left unchecked, the disease could undo decades of conservation work in the blink of an eye."

Wild birds often spread HPAI during seasonal migrations. In Arizona, free-flying condors were affected by an outbreak earlier this year. To combat the problem, the USDA approved a vaccine for a pilot study, according to the Oregon Zoo.

The vaccine will be evaluated, and authorities will decide whether to vaccinate wild condors.

"Collaboration with our zoological partners has been vital for the implementation of this trial," said Ashleigh Blackford, California Condor Recovery Program coordinator for the Fish and Wildlife Service. "None of this important work would be possible without the collaboration from all our partners."

Four condors received an initial vaccine dose plus a booster at the Oregon Zoo's veterinary medical center. Five more birds served as a control group at the zoo’s offsite condor recovery center.

"California condors exist today because of a powerful conservation partnership and our communities’ commitment to their survival," said Travis Koons, who oversees the zoo’s bird populations and northwest species recovery efforts. "An incredibly dedicated, talented team has once again come together to take action in crisis, giving me hope that even as new threats emerge, we’ll be able to ensure the long-term survival of this majestic species."

The California condor, listed under the Endangered Species Act, was critically endangered, with only 22 individuals remaining in the wild by 1982. The last condors were brought into human care in 1987 to save the species from extinction.