Houston may have just handed baby elephants a lifeline. Researchers here are celebrating a major milestone in elephant conservation after an mRNA vaccine developed by the Houston Zoo and Baylor College of Medicine appears to protect elephants from a deadly herpesvirus. The shot, first administered at the Houston Zoo in June 2024, has since been used at several U.S. institutions, and early reports suggest it can stop the rapid, often fatal disease that kills juvenile Asian elephants.
The Cincinnati Zoo reported that two young males, Sanjay and Kabir, who were vaccinated in 2024 and later tested positive for EEHV, are now testing negative. Zoo staff say the vaccinated calves developed durable antibody responses and cleared low-level infections without progressing to severe disease.
How Houston built the shot
The vaccine grew out of a long-running partnership between the Houston Zoo and virologist Dr. Paul Ling at Baylor College of Medicine that began after the zoo lost a young calf, Mac, to EEHV. According to the Houston Zoo, the first field dose was given to Tess, a 40-year-old Asian elephant, on June 18, 2024, and zoo veterinarians have closely monitored her antibody levels and overall health since the injection.
Early results from other herds
Other AZA-accredited institutions have joined the effort as word of Houston's work spread. Fort Worth's calf Brazos received two doses, and Syracuse's Rosamond Gifford Zoo has vaccinated its rare twin calves as part of coordinated testing, officials say. The Fort Worth Zoo and local outlets in Syracuse reported the vaccinations as researchers collect blood samples to track immune responses across different animals.
Why veterinarians are hopeful
Elephant endotheliotropic herpesvirus, or EEHV, has been the leading cause of death for juvenile Asian elephants in human care and carries a high fatality rate in symptomatic cases. The Association of Zoos and Aquariums and conservation groups say an effective vaccine could dramatically reduce those losses and change how zoos and scientists protect endangered herds.
Researchers caution that the program is still in its early stages and that wider rollout will require more data, production capacity, and coordinated protocols. Even so, partners, including funders such as Colossal Biosciences and conservation organizations, say the early outcomes are promising for animals in human care and, eventually, at-risk wild populations. As teams expand monitoring and add animals to the trial, Houston's decades-long research push could become a global tool against a disease that has long threatened the future of Asian elephants.
