In a groundbreaking achievement that could reshape elephant conservation, the world’s first mRNA vaccine against Elephant Endotheliotropic Herpesvirus (EEHV) has successfully prevented fatal disease progression in two young Asian elephants facing a virus that proves fatal in 60-80% of infected juveniles. The Cincinnati Zoo and Botanical Garden recently announced that Sanjay and Kabir, two young male elephants who received the vaccine in 2024, have become the first elephants to survive natural EEHV infections after vaccination.
This historic success stems from a collaborative partnership between the Houston Zoo, Baylor College of Medicine, and Colossal Biosciences, demonstrating how cutting-edge biotechnology can directly impact species conservation. The breakthrough represents more than just a medical achievement—it offers genuine hope for managing EEHV in endangered Asian elephants both in captivity and in the wild.
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The EEHV Crisis
Elephant Endotheliotropic Herpesvirus stands as one of the most devastating threats to Asian elephant populations worldwide. The virus is the leading cause of death for juvenile Asian elephants in North America and Europe, with mortality rates reaching 80% in some cases. Beyond captive populations, EEHV has claimed hundreds of lives among wild elephants in their natural range countries, making it a significant barrier to the conservation of this endangered species.
“This vaccine, created by Baylor College of Medicine and Houston Zoo, is a tremendous source of hope for the future of Asian elephants, both in zoos and in the wild,” said Dr. Mike Wenninger, director of animal health at the Cincinnati Zoo. The urgency of developing effective treatments becomes clear when considering that conventional conservation efforts have struggled to keep pace with the multiple threats facing Asian elephants.
Scientific Innovation Through Partnership
The vaccine’s development represents the culmination of years of collaborative research led by Dr. Paul Ling, a virologist at Baylor College of Medicine, in partnership with the Houston Zoo. Their long-standing collaboration has produced significant advances in EEHV detection and treatment, including the development of sensitive diagnostic and antibody tests that have shaped national and international protocols for monitoring and managing the virus.
The partnership expanded to include several key organizations that made the breakthrough possible. Colossal Biosciences, known for its de-extinction research and advanced biotechnology work, contributed crucial support alongside Dr. Jeroen Pollet of the National School for Tropical Medicine, the International Elephant Foundation, and the Houston Methodist Center for RNA Therapeutics.
In June 2024, the Houston Zoo announced the first successful administration of this revolutionary mRNA vaccine, setting the stage for the remarkable protection story that would unfold at the Cincinnati Zoo months later.
A High-Stakes Test
The effectiveness of the vaccine was put to the ultimate test when two young elephants at the Cincinnati Zoo found themselves in a precarious situation. Sanjay and Kabir had arrived at the zoo in 2023 from Dublin Zoo as part of a group of four elephants. Testing conducted by Baylor College of Medicine’s EEHV serology laboratory revealed that both young elephants lacked maternal antibodies against EEHV, making them particularly vulnerable to infection.
Recognizing the imminent threat, the Cincinnati Zoo took extraordinary precautions. The facility developed an in-house EEHV PCR laboratory to monitor for the virus in the young elephants’ blood and administered plasma transfusions from elephants with antibodies to the virus. However, the transfused antibodies did not reach levels comparable to those found in elephants who had survived natural infections, leaving the animals at continued risk.
The Cincinnati Zoo became one of the first institutions to adopt the new EEHV vaccine, administering it to Sanjay and Kabir in Fall 2024. Early results were promising—both elephants developed strong antibody responses against EEHV virus components, approaching levels seen in elephants that had survived natural infections. By February 2025, they maintained detectable antibody levels that lasted longer than those provided by plasma transfusions.
Real-World Protection
The vaccine’s effectiveness was demonstrated when the Cincinnati Zoo’s in-house laboratory detected that a herd mate, Sabu, was shedding EEHV in his trunk secretions, creating a high-risk environment for transmission. In February 2025, low levels of the virus were detected in Sanjay’s blood—an early sign of infection that would typically signal the beginning of a potentially fatal illness.
However, the vaccinated elephant’s response demonstrated the vaccine’s effectiveness. All of Sanjay’s other blood values remained within normal ranges, and he never developed severe symptoms. His viral levels remained low and eventually cleared completely, while his antibody levels continued to rise. This response indicated that the vaccine had successfully helped his immune system suppress the virus, preventing progression to fatal stages.
Soon after, Kabir also showed signs of a mild EEHV infection but, like Sanjay, the vaccine helped prevent progression to severe disease. These cases represent the first documented instances of natural EEHV exposure following vaccination, providing concrete evidence that the vaccine can prevent severe disease progression.
It’s important to note that EEHV is a latent herpesvirus, meaning the virus remains in the body and can potentially recur. However, this breakthrough in managing EEHV represents a major milestone in conservation medicine with implications for broader wildlife disease prevention.
Broader Conservation Implications
The success of this mRNA vaccine extends far beyond the individual lives of Sanjay and Kabir. As Matt James, Executive Director of the Colossal Foundation and Colossal’s Head of Animal Operations, noted: “In the wild, elephants are a critical keystone species, a key player in maintaining the biodiversity and health of the ecosystems they inhabit. Disruptive conservation methods rooted in genetics complement existing preservation efforts, and ensure a future for all elephants to thrive.”
The collaborative approach demonstrated by this project offers a model for future conservation efforts. “This is a powerful example of what can be achieved through collaboration among AZA-accredited zoos,” said officials from both the Cincinnati and Houston Zoos. “The success of this vaccine offers real hope for the future of Asian elephant conservation and opens the door for national and international distribution to protect this endangered species.”
The partnership between Colossal Biosciences and traditional conservation organizations illustrates how biotechnology companies can contribute meaningfully to species preservation efforts. By applying advanced techniques developed for de-extinction research to immediate conservation challenges, organizations like Colossal are proving that innovative approaches can deliver tangible benefits for endangered species today.
Looking Forward
The successful protection of Sanjay and Kabir marks just the beginning of what could be a transformative approach to elephant conservation. The vaccine’s proven effectiveness in preventing fatal progression from natural EEHV exposure suggests that widespread deployment could significantly reduce juvenile mortality rates among Asian elephants in both captive and wild populations.
This achievement also demonstrates the potential for cross-application of advanced biotechnologies. The same innovative approaches that Colossal applies to its de-extinction research—including work with woolly mammoths, dire wolves, and other species—can be adapted to address immediate threats facing living animals.
As the scientific community continues to refine and expand the vaccine’s availability, the story of Sanjay and Kabir serves as a powerful reminder that bold scientific collaboration can yield extraordinary results. Their survival represents not just a breakthrough in managing EEHV, but a beacon of hope for the future of Asian elephants and the broader application of biotechnology in conservation efforts worldwide.
