A highly contagious form of avian flu (H5N1) has infected marine mammal populations worldwide. Since the highly pathogenic strain form was first recorded, more than 20,000 sea lions have died in Chile and Peru and more than 17,000 southern elephant seal pups have died in Argentina. In response, the world's largest marine mammal hospital has begun a vaccine trial seeking to protect the health and welfare of marine mammals.

Although the first known outbreak of avian influenza is thought to have occurred in Italy in 1878, the highly pathogenic strain known as H5N1 was not recognized until 1996. A specific strain of influenza A, H5N1 is a highly contagious respiratory disease. It primarily affects birds - both wild and domestic - but has increasingly been found to infect mammals including dairy cows, seals and sea lions, and even cetaceans.

The worldwide outbreak of avian flu that began in 2020 has caused economic turmoil as it spreads through farming operations. It is also causing havoc in ecosystems as it decimates populations of marine mammals, since it can take species decades to recover. Notable outbreaks of the virus have occurred on the east and west coasts of the US, the St. Lawrence Estuary in Canada, in Chile and Peru, in Dagestan, Russia, and even in Antarctica.

Transmission of H5N1 occurs from direct contact with an infected bird or with a contaminated surface. As infected birds migrate between countries and continents, they expand the areas subject to contamination. The opportunity for transmission between sea birds and seals and sea lions exists because marine mammals are often in proximity to sea birds.

It was not until the appearance of the new highly contagious variant that the consequences of contracting the disease became dire. Scientists believe that the highly pathologic virus no longer requires the bird-to-mammal link for transmission. Instead, it appears that mammals can spread the virus among themselves. For example, in 2022 a mink farm in Spain experienced viral transmission that triggered the need to euthanize 50,000 animals. A University of Massachusetts biologist proclaimed it as a "new era" for bird flu.

Avian flu infections also have been reported in cetaceans, with the findings of a dead bottlenose dolphin in Florida, two more in the United Kingdom, and a harbor porpoise in Sweden. Some classify these as unusual mortality events.

The Marine Mammal Center, the world's largest marine mammal hospital with facilities located in the San Francisco Bay area and Hawaii are taking decisive steps to slow down the virus.

While the Center's patients have tested negative for the virus thus far, there is increasing concern for the critically endangered Hawaiian monk seal population. There are only about 1,600 Hawaiian monk seals alive today and they have no known natural immunity to the virus. Concern grew to actionable levels when a wild duck on Hawaii's Oahu Island was detected with the disease.

Two separate areas of research have informed the Center's next steps.

In one, the US Fish and Wildlife Service began trials of an H5N1 vaccine on the critically endangered California condor. The other is the US Department of Agriculture's conditional licensure of avian flu vaccine testing on dairy cows. The vaccine - manufactured by Zoetis, Inc., a New Jersey-based producer of vaccines for pets and livestock - has a long track record for developing vaccines to address avian influenza. It was a Zoetis vaccine that was first used by the US Fish & Wildlife Service in the California condors study.

Before vaccinating the endangered Hawaiian monk seals, researchers at the Marine Mammal Center needed to understand the vaccine's safety and efficacy on a similar but non-endangered marine species.

A carefully designed trial with northern elephant seals began in July of this year. Elephant seals were chosen as surrogate species for the monk seals. Because there is not currently a bird flu vaccine produced specifically for marine mammals, they administered Zoetis' vaccine developed for cows.

The six elephant seals used in the trial were treated at the California marine mammal hospital, having been rescued as they were suffering from severe malnutrition. The six were selected based on their current state of health and likelihood of release. Three seals received a series of two vaccine doses three weeks apart. The other three served as the control group. They received no vaccine, only injections of sterile saline.

The study is in the evaluation stage, with initial findings that the avian flu vaccine appears to be safely used with the six elephant seals. The next step is to assess levels of antibodies in the animals' blood. If a vaccinated seal's blood shows the existence of specific antibodies, it suggests that the individual developed protective immunity to bird flu.

The Marine Mammal Center's research is an important first step not only in developing important protection for the endangered Hawaiian monk seals but other at risk marine mammal populations worldwide. This work is critical because, as the World Organisation for Animal Health has pointed out, "[t]he loss of wildlife at the current scale presents an unprecedented risk of wildlife population collapse, creating an ecological crisis."

Vaccine Trials Underway to Protect Marine Animals from Avian Flu