The world's first vaccine trial against elephant endotheliotropic herpesvirus proves safe and effective

The world's first vaccine trial against elephant endotheliotropic herpesvirus proves safe and effective

The world's first vaccine trial against elephant endotheliotropic herpesvirus (EEHV) - a common cause of death in young Asian elephants - is safe and triggers a strong virus-fighting immune response, according to an international team led by the University of Surrey in collaboration with Chester Zoo and the Animal and Plant Health Agency.

The proof-of-concept study, published in Nature Communications, involved adult elephants at Chester Zoo. No side effects were observed and the vaccine successfully activated an important part of the immune system that helps fight viruses.

The elephants received a two-stage vaccination: first a viral vector carrying two EEHV proteins (EE2 and major capsid protein), then a booster vaccination with purified proteins and an adjuvant to enhance the response. Blood samples were tested in a variety of ways, including using whole transcriptome sequencing to see which immune pathways were activated - the first time such systematic immune profiling has been performed in elephants.

The results suggest the vaccine could prevent fatal EEHV disease in calves - the group most at risk - and support conservation breeding programs worldwide.

Professor Falko Steinbach, lead author of the study and Professor of Veterinary Immunology at the University of Surrey, said:

"This is a milestone in our work to develop safe and effective vaccines. For the first time in elephants, we have shown that a vaccine can trigger the type of immune response needed to protect against EEHV."

Dr. Tanja Maehr, lead author of the Animal and Plant Health Agency study, said:

"Our results provide hope that vaccination may be a practical tool for preventing serious illness and death from EEHV. The next step may be to test the vaccine in calves and in distribution areas so we can begin to protect those most at risk."

In particular, the vaccine activated two key types of immune cells - CD4+ and CD8+ T cells (often called "helper cells" and "killer cells") - which control the immune system's fight against viruses. A systems immunology analysis – carried out in collaboration between the University of Surrey and São Paulo – confirmed the broad activation of antiviral immunity.

These results show that a two-stage vaccine can safely prepare the elephant's immune system to fight EEHV.

This vaccine has been in development for several years and was first administered to an elephant here at Chester Zoo in 2021. This publication marks a turning point.

EEHV has claimed the lives of so many elephants, both in human care and in the wild, but this vaccine offers hope. We can’t say yet that this will be the end of EEHV deaths, but we are a big step closer to that goal.”

Dr. Katie Edwards, senior conservation scientist at Chester Zoo

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