Two wild Hawaiian monk seals, an endangered species, have become the first of their kind to receive vaccines for bird flu, part of a new effort to protect the animals from a virus that has been ravaging marine mammal populations around the world.

The vaccinations represent the next phase of a small study that began this summer in northern elephant seals, which are not endangered. The vaccine appeared to be safe for elephant seals, the researchers found, and prompted the marine mammals to begin making antibodies against the virus, which is known as H5N1.

The quick move to include monk seals was also driven by the discovery that the virus had recently returned to Hawaii; the state’s remote location had previously helped protect the monk seals from the ongoing outbreak.

“This is a real, real threat to the population,” said Dr. Sophie Whoriskey, the associate director of Hawai’i Conservation Medicine at the Marine Mammal Center, which is leading the study in consultation with the National Oceanic and Atmospheric Administration.

Hawaiian monk seals, which were hunted nearly to extinction in the 19th century, face a variety of ongoing threats, including habitat loss, the risk of entanglement in fishing gear and a limited food supply. Over the last decade or so, the population has finally begun to rebound, thanks to intensive conservation efforts, but the species is still in a precarious position; just 1,600 Hawaiian monk seals remain in the wild.

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