Vaccine for elephant herpesvirus found to be safe

A vaccine trial against elephant endotheliotropic herpesvirus (EEHV) — a leading cause of death in young Asian elephants — has proved the vaccine is safe and triggers a strong virus-fighting immune response, according to an international team led by the University of Surrey, Chester Zoo, and the Animal and Plant Health Agency (APHA).

With the ability to kill elephants in just 24 hours, EEHV poses a severe threat to the survival of Asian elephants — a species already listed as Endangered on the IUCN Red List. Fatal cases have been documented across India, Nepal, Myanmar, Thailand and beyond, with the disease affecting both wild populations and vital conservation breeding programs in zoos worldwide. The virus has also been detected in African elephants.

The proof‑of‑concept study saw adult elephants at Chester Zoo receive a two‑step vaccination: first, a viral vector carrying two EEHV proteins (EE2 and major capsid protein), then a booster with purified proteins plus an adjuvant to strengthen the response. Blood samples were then tested in various ways, including using whole transcriptome sequencing to see which immune pathways were switched on. This is understood to be the first time such systematic immune profiling has been carried out in elephants.

The study’s results, published in the journal Nature Communications, found that the vaccine successfully activated a key part of the immune system that helps fight viruses, with no noticeable side effects observed. This suggests the vaccine could prevent deadly EEHV disease in calves — the group most at risk — and support conservation breeding programs worldwide.

“This is a landmark moment in our work to develop safe and efficacious vaccines,” said Professor Falko Steinbach, from the University of Surrey and APHA. “For the first time, we have shown in elephants that a vaccine can trigger the type of immune response needed to protect them against EEHV.”

Specifically, the vaccine activated two key types of immune cells — CD4⁺ and CD8⁺ T cells (often called ‘helper’ and ‘killer’ cells) — that mediate the immune system’s fight against viruses. Systems immunology analysis, carried out between the Universities of Surrey and São Paulo, confirmed the broad activation of antiviral immunity.

“Our findings give real hope that vaccination can become a practical tool for preventing severe disease and death due to EEHV,” said lead author Dr Tanja Maehr, from APHA. “The next step could be to trial the vaccine in calves and in range countries, so we can begin to protect those most at risk.”

Image caption: Indali Hi-Way (left), born at Chester Zoo in 2016, is one of only a handful of recorded survivors of EEHV after intensive treatment in 2019. Image credit: Chester Zoo.